Internet DRAFT - draft-ietf-bess-rfc7432bis
draft-ietf-bess-rfc7432bis
BESS Working Group A. Sajassi, Ed.
Internet-Draft LA. Burdet
Obsoletes: 7432 (if approved) Cisco
Updates: 8214 (if approved) J. Drake
Intended status: Standards Track Juniper
Expires: 16 August 2024 J. Rabadan
Nokia
13 February 2024
BGP MPLS-Based Ethernet VPN
draft-ietf-bess-rfc7432bis-08
Abstract
This document describes procedures for Ethernet VPN (EVPN), a BGP
MPLS-based solution which addresses the requirements specified in the
corresponding RFC - "Requirements for Ethernet VPN (EVPN)".
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 16 August 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Summary of changes from RFC 7432 . . . . . . . . . . . . 4
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 6
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. BGP MPLS-Based EVPN Overview . . . . . . . . . . . . . . . . 8
5. Ethernet Segment . . . . . . . . . . . . . . . . . . . . . . 9
6. Ethernet Tag ID . . . . . . . . . . . . . . . . . . . . . . . 12
6.1. VLAN-Based Service Interface . . . . . . . . . . . . . . 13
6.2. VLAN Bundle Service Interface . . . . . . . . . . . . . . 13
6.2.1. Port-Based Service Interface . . . . . . . . . . . . 13
6.3. VLAN-Aware Bundle Service Interface . . . . . . . . . . . 14
6.3.1. Port-Based VLAN-Aware Service Interface . . . . . . . 14
6.4. EVPN PE Model . . . . . . . . . . . . . . . . . . . . . . 15
7. BGP EVPN Routes . . . . . . . . . . . . . . . . . . . . . . . 16
7.1. Ethernet Auto-Discovery Route . . . . . . . . . . . . . . 17
7.2. MAC/IP Advertisement Route . . . . . . . . . . . . . . . 18
7.3. Inclusive Multicast Ethernet Tag Route . . . . . . . . . 19
7.4. Ethernet Segment Route . . . . . . . . . . . . . . . . . 19
7.5. ESI Label Extended Community . . . . . . . . . . . . . . 20
7.6. ES-Import Route Target . . . . . . . . . . . . . . . . . 21
7.7. MAC Mobility Extended Community . . . . . . . . . . . . . 22
7.8. Default Gateway Extended Community . . . . . . . . . . . 23
7.9. Route Distinguisher Assignment per MAC-VRF . . . . . . . 23
7.10. Route Targets . . . . . . . . . . . . . . . . . . . . . . 23
7.10.1. Auto-derivation from the Ethernet Tag (VLAN ID) . . 24
7.11. EVPN Layer 2 Attributes Extended Community . . . . . . . 24
7.11.1. EVPN Layer 2 Attributes Partitioning . . . . . . . . 25
7.11.2. EVPN Layer 2 Attributes Negotiation . . . . . . . . 27
7.12. Route Prioritization . . . . . . . . . . . . . . . . . . 27
7.13. Best Path Selection . . . . . . . . . . . . . . . . . . . 28
7.13.1. Best Path Selection for MAC/IP Advertisement
routes . . . . . . . . . . . . . . . . . . . . . . . 28
7.13.2. Best Path Selection for Ethernet A-D per EVI
routes . . . . . . . . . . . . . . . . . . . . . . . 29
7.13.3. Best Path Selection for Inclusive Multicast Ethernet
Tag routes . . . . . . . . . . . . . . . . . . . . . 30
8. Multihoming Functions . . . . . . . . . . . . . . . . . . . . 30
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8.1. Multihomed Ethernet Segment Auto-discovery . . . . . . . 30
8.1.1. Constructing the Ethernet Segment Route . . . . . . . 30
8.2. Fast Convergence . . . . . . . . . . . . . . . . . . . . 31
8.2.1. Constructing Ethernet A-D per Ethernet Segment
Route . . . . . . . . . . . . . . . . . . . . . . . . 31
8.2.1.1. Ethernet A-D Route Targets . . . . . . . . . . . 32
8.3. Split Horizon . . . . . . . . . . . . . . . . . . . . . . 32
8.3.1. ESI Label Assignment . . . . . . . . . . . . . . . . 33
8.3.1.1. Ingress Replication . . . . . . . . . . . . . . . 33
8.3.1.2. P2MP MPLS LSPs . . . . . . . . . . . . . . . . . 34
8.3.1.3. MP2MP MPLS LSPs . . . . . . . . . . . . . . . . . 35
8.4. Aliasing and Backup Path . . . . . . . . . . . . . . . . 36
8.4.1. Constructing Ethernet A-D per EVPN Instance Route . . 37
8.5. Designated Forwarder Election . . . . . . . . . . . . . . 38
8.6. Signaling Primary and Backup DF Elected PEs . . . . . . . 40
8.7. Interoperability with Single-Homing PEs . . . . . . . . . 40
9. Determining Reachability to Unicast MAC Addresses . . . . . . 41
9.1. Local Learning . . . . . . . . . . . . . . . . . . . . . 41
9.2. Remote Learning . . . . . . . . . . . . . . . . . . . . . 41
9.2.1. Constructing MAC/IP Address Advertisement . . . . . . 42
9.2.2. Route Resolution . . . . . . . . . . . . . . . . . . 43
10. ARP and ND . . . . . . . . . . . . . . . . . . . . . . . . . 45
10.1. Default Gateway . . . . . . . . . . . . . . . . . . . . 46
10.1.1. Best Path Selection for Default Gateway . . . . . . 47
11. Handling of Multi-destination Traffic . . . . . . . . . . . . 47
11.1. Constructing Inclusive Multicast Ethernet Tag Route . . 47
11.2. P-Tunnel Identification . . . . . . . . . . . . . . . . 48
12. Processing of Unknown Unicast Packets . . . . . . . . . . . . 49
12.1. Ingress Replication . . . . . . . . . . . . . . . . . . 50
12.2. P2MP MPLS LSPs . . . . . . . . . . . . . . . . . . . . . 50
13. Forwarding Unicast Packets . . . . . . . . . . . . . . . . . 50
13.1. Forwarding Packets Received from a CE . . . . . . . . . 51
13.2. Forwarding Packets Received from a Remote PE . . . . . . 52
13.2.1. Unknown Unicast Forwarding . . . . . . . . . . . . . 52
13.2.2. Known Unicast Forwarding . . . . . . . . . . . . . . 52
14. Load Balancing of Unicast Packets . . . . . . . . . . . . . . 52
14.1. Load Balancing of Traffic from a PE to Remote CEs . . . 52
14.1.1. Single-Active Redundancy Mode . . . . . . . . . . . 53
14.1.2. All-Active Redundancy Mode . . . . . . . . . . . . . 53
14.2. Load Balancing of Traffic between a PE and a Local CE . 55
14.2.1. Data-Plane Learning . . . . . . . . . . . . . . . . 55
14.2.2. Control-Plane Learning . . . . . . . . . . . . . . . 55
15. MAC Mobility . . . . . . . . . . . . . . . . . . . . . . . . 55
15.1. MAC Duplication Issue . . . . . . . . . . . . . . . . . 57
15.2. Sticky MAC Addresses . . . . . . . . . . . . . . . . . . 58
15.3. Loop Protection . . . . . . . . . . . . . . . . . . . . 58
16. Multicast and Broadcast . . . . . . . . . . . . . . . . . . . 60
16.1. Ingress Replication . . . . . . . . . . . . . . . . . . 60
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16.2. P2MP or MP2MP LSPs . . . . . . . . . . . . . . . . . . . 60
16.2.1. Inclusive Trees . . . . . . . . . . . . . . . . . . 60
17. Convergence . . . . . . . . . . . . . . . . . . . . . . . . . 61
17.1. Transit Link and Node Failures between PEs . . . . . . . 61
17.2. PE Failures . . . . . . . . . . . . . . . . . . . . . . 61
17.3. PE-to-CE Network Failures . . . . . . . . . . . . . . . 61
18. Frame Ordering . . . . . . . . . . . . . . . . . . . . . . . 62
18.1. Flow Label . . . . . . . . . . . . . . . . . . . . . . . 63
19. Use of Domain-wide Common Block (DCB) Labels . . . . . . . . 64
20. Security Considerations . . . . . . . . . . . . . . . . . . . 64
21. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 66
22. References . . . . . . . . . . . . . . . . . . . . . . . . . 66
22.1. Normative References . . . . . . . . . . . . . . . . . . 67
22.2. Informative References . . . . . . . . . . . . . . . . . 68
Appendix A. Acknowledgments for This Document (2022) . . . . . . 70
Appendix B. Contributors for This Document (2021) . . . . . . . 71
Appendix C. Acknowledgments from the First Edition (2015) . . . 71
C.1. Contributors from the First Edition (2015) . . . . . . . 71
C.2. Authors from the First Edition (2015) . . . . . . . . . . 72
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 72
1. Introduction
Virtual Private LAN Service (VPLS), as defined in [RFC4664],
[RFC4761], and [RFC4762], is a proven and widely deployed technology.
However, the existing solution has a number of limitations when it
comes to multihoming and redundancy, multicast optimization,
provisioning simplicity, flow-based load balancing, and multipathing;
these limitations are important considerations for Data Center (DC)
deployments. [RFC7209] describes the motivation for a new solution
to address these limitations. It also outlines a set of requirements
that the new solution must address.
This document describes procedures for a BGP MPLS-based solution
called Ethernet VPN (EVPN) to address the requirements specified in
[RFC7209]. Please refer to [RFC7209] for the detailed requirements
and motivation. EVPN requires extensions to existing IP/MPLS
protocols as described in this document. In addition to these
extensions, EVPN uses several building blocks from existing MPLS
technologies.
1.1. Summary of changes from RFC 7432
This section describes the significant changes between [RFC4762] and
this document.
* Updates to Terminology i.a. BD, EVI, Ethernet Tag ID, P-tunnel,
DF/BDF/NDF, DCB;
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* Added Section 6.4 for description and disambiguation of EVPN
bridging terminology;
* Added ES-Import route target auto-derivation for ESI types 0,4,5;
* Precision of 'encoding' language for all references to 'Label'
fields;
* Added Section 7.11 for usage of EVPN Layer 2 Attributes Extended
Community in EVPN Bridging;
* Added Section 7.12 proposes relative order-of-magnitude route
priority and processing to help achieve fast convergence;
* Corrected Section 8.2.1 to include reference to E-TREE exception;
* Updated Section 8.5 to include Backup- and Non-Designated
Forwarder roles to DF-Election algorithm, description of those
roles and signaling updates;
* Updated Section 8.5 to specify DF Election behaviour for
Originating IP in different family
* Added Section 8.3.1.3 for MP2MP MPLS LSPs and updated
Section 12.2;
* High-level Best Path algorithm description for EVPN in
Section 7.13;
* Address conflicts in Best Path algorithm for Default Gateway in
Section 10.1.1;
* Update to Section 14.1.1 redundancy mode description;
* Added Section 15.3 describing a loop detection and protection
mechanism;
* Added Section 18.1 describing Flow-label usage and signaling (see
also new Section 7.11);
* Section 19 specifies use of Domain-wide Common Block (DCB) for
several cases;
* Restructuring, namely Section 8.5 to Section 5, simplify all
Ethernet Tag ID references to Section 6 ; and
* Corrected Route Target and other extcomm 'attributes' references
to 'extended communities';
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* Cross-references and editorial changes; [RFC7991] and xml2rfc-v3
update (source).
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Terminology
BD: Broadcast Domain. In a bridged network, the broadcast domain
corresponds to a Virtual LAN (VLAN), where a VLAN is typically
represented by a single VLAN ID (VID) but can be represented by
several VIDs where Shared VLAN Learning (SVL) is used per
[IEEE.802.1Q_2014].
Bridge Table: An instantiation of a broadcast domain on a MAC-VRF.
CE: Customer Edge device, e.g., a host, router, or switch.
EVI: An EVPN instance spanning the Provider Edge (PE) devices
participating in that EVPN. An EVI may be comprised of one BD
(VLAN-based, VLAN Bundle, or Port-based services) or multiple BDs
(VLAN-aware Bundle or Port-based VLAN-Aware services).
MAC-VRF: A Virtual Routing and Forwarding table for Media Access
Control (MAC) addresses on a PE.
Ethernet Segment (ES): When a customer site (device or network) is
connected to one or more PEs via a set of Ethernet links, then
that set of links is referred to as an 'Ethernet segment'.
Ethernet Segment Identifier (ESI): A unique non-zero identifier that
identifies an Ethernet segment is called an 'Ethernet Segment
Identifier'.
VID: VLAN Identifier.
Ethernet Tag: Used to represent a BD that is configured on a given
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ES for the purposes of DF election and <EVI, BD> identification
for frames received from the CE. Note that any of the following
may be used to represent a BD: VIDs (including Q-in-Q tags),
configured IDs, VNIs (Virtual Extensible Local Area Network
(VXLAN) Network Identifiers), normalized VIDs, I-SIDs (Service
Instance Identifiers), etc., as long as the representation of the
BDs is configured consistently across the multihomed PEs attached
to that ES.
Ethernet Tag ID: Normalized network wide ID that is used to identify
a BD within an EVI and carried in EVPN routes.
LACP: Link Aggregation Control Protocol.
MP2MP: Multipoint to Multipoint.
MP2P: Multipoint to Point.
P2MP: Point to Multipoint.
P2P: Point to Point.
P-tunnel: A tunnel through the network of one or more service
providers. In this document, P-tunnels are instantiated as
bidirectional multicast distribution trees.
PE: Provider Edge device.
Single-Active Redundancy Mode: When only a single PE, among all the
PEs attached to an Ethernet segment, is allowed to forward traffic
to/from that Ethernet segment for a given VLAN, then the Ethernet
segment is defined to be operating in Single-Active redundancy
mode.
All-Active Redundancy Mode: When all PEs attached to an Ethernet
segment are allowed to forward known unicast traffic to/from that
Ethernet segment for a given VLAN, then the Ethernet segment is
defined to be operating in All-Active redundancy mode.
BUM: Broadcast, unknown unicast, and multicast.
DF: Designated Forwarder.
Backup-DF (BDF): Backup-Designated Forwarder.
Non-DF (NDF): Non-Designated Forwarder.
DCB: Domain-wide Common Block (of labels), as in
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[I-D.ietf-bess-mvpn-evpn-aggregation-label].
AC: Attachment Circuit.
NVO: Network Virtualization Overlay as decribed in [RFC8365]
IRB: Integrated Routing and Bridging interface, with EVPN procedures
described in [RFC9135]
4. BGP MPLS-Based EVPN Overview
This section provides an overview of EVPN. An EVPN instance
comprises Customer Edge devices (CEs) that are connected to Provider
Edge devices (PEs) that form the edge of the MPLS infrastructure. A
CE may be a host, a router, or a switch. The PEs provide virtual
Layer 2 bridged connectivity between the CEs. There may be multiple
EVPN instances in the provider's network.
The PEs may be connected by an MPLS Label Switched Path (LSP)
infrastructure, which provides the benefits of MPLS technology, such
as fast reroute, resiliency, etc. The PEs may also be connected by
an IP infrastructure, in which case IP/GRE (Generic Routing
Encapsulation) tunneling or other IP tunneling can be used between
the PEs. The detailed procedures in this document are specified only
for MPLS LSPs as the tunneling technology. However, these procedures
are designed to be extensible to IP tunneling as the Packet Switched
Network (PSN) tunneling technology.
In an EVPN, MAC learning between PEs occurs not in the data plane (as
happens with traditional bridging in VPLS [RFC4761] [RFC4762]) but in
the control plane. Control-plane learning offers greater control
over the MAC learning process, such as restricting who learns what,
and the ability to apply policies. Furthermore, the control plane
chosen for advertising MAC reachability information is multi-protocol
(MP) BGP (similar to IP VPNs [RFC4364]). This provides flexibility
and the ability to preserve the "virtualization" or isolation of
groups of interacting agents (hosts, servers, virtual machines) from
each other. In EVPN, PEs advertise the MAC addresses learned from
the CEs that are connected to them, along with an MPLS label, to
other PEs in the control plane using Multiprotocol BGP (MP-BGP).
Control-plane learning enables load balancing of traffic to and from
CEs that are multihomed to multiple PEs. This is in addition to load
balancing across the MPLS core via multiple LSPs between the same
pair of PEs. In other words, it allows CEs to connect to multiple
active points of attachment. It also improves convergence times in
the event of certain network failures.
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However, learning between PEs and CEs is done by the method best
suited to the CE: data-plane learning, IEEE 802.1x, the Link Layer
Discovery Protocol (LLDP), IEEE 802.1aq, Address Resolution Protocol
(ARP), management plane, or other protocols.
It is a local decision as to whether the Layer 2 forwarding table on
a PE is populated with all the MAC destination addresses known to the
control plane, or whether the PE implements a cache-based scheme.
For instance, the MAC forwarding table may be populated only with the
MAC destinations of the active flows transiting a specific PE.
The policy attributes of EVPN are very similar to those of IP-VPN.
An EVPN instance requires a Route Distinguisher (RD) that is unique
per MAC-VRF and one or more globally unique Route Targets (RTs). A
CE attaches to a BD, on a PE, using an Ethernet interface that may be
configured for one or more Ethernet tags. If the Ethernet tags are
VLAN IDs, some deployment scenarios guarantee uniqueness of VLAN IDs
across EVPN instances: all points of attachment for a given EVPN
instance use the same VLAN ID, and no other EVPN instance uses this
VLAN ID. This document refers to this case as a "Unique VLAN EVPN"
and describes simplified procedures to optimize for it. See for
example Section 7.10.1 which describes deriving automatically the
RT(s) for each EVPN instance from the corresponding VID.
5. Ethernet Segment
As indicated in [RFC7209], each Ethernet segment needs a unique
identifier in an EVPN. This section defines how such identifiers are
assigned and how they are encoded for use in EVPN signaling. Later
sections of this document describe the protocol mechanisms that
utilize the identifiers.
When a customer site is connected to one or more PEs via a set of
Ethernet links, then this set of Ethernet links constitutes an
"Ethernet segment". For a multihomed site, each Ethernet segment
(ES) is identified by a unique non-zero identifier called an Ethernet
Segment Identifier (ESI). An ESI is encoded as a 10-octet integer in
line format with the most significant octet sent first. The
following two ESI values are reserved:
- ESI {0x00} (repeated 10 times), or ESI 0, denotes a single-homed
site.
- ESI {0xFF} (repeated 10 times) is known as MAX-ESI and is reserved.
In general, an Ethernet segment SHOULD have a non-reserved ESI that
is unique network wide (i.e., across all EVPN instances on all the
PEs). If the CE(s) constituting an Ethernet segment is (are) managed
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by the network operator, then ESI uniqueness should be guaranteed;
however, if the CE(s) is (are) not managed, then the operator MUST
configure a network-wide unique ESI for that Ethernet segment. This
is required to enable auto-discovery of Ethernet segments and
Designated Forwarder (DF) election.
In a network with managed and non-managed CEs, the ESI has the
following format:
+---+---+---+---+---+---+---+---+---+---+
| T | ESI Value |
+---+---+---+---+---+---+---+---+---+---+
Where:
T (ESI Type) is a 1-octet field (most significant octet) that
specifies the format of the remaining 9 octets (ESI Value). The
following six ESI types can be used:
* Type 0 (T=0x00) - This type indicates an arbitrary 9-octet ESI
value, which is managed and configured by the operator.
* Type 1 (T=0x01) - When IEEE 802.1AX LACP is used between the PEs
and CEs, this ESI type indicates an auto-generated ESI value
determined from LACP by concatenating the following parameters:
- CE LACP System MAC address (6 octets). The CE LACP System MAC
address MUST be encoded in the high-order 6 octets of the ESI
Value field.
- CE LACP Port Key (2 octets). The CE LACP port key MUST be
encoded in the 2 octets next to the System MAC address.
- The remaining octet SHOULD be set to 0x00.
As far as the CE is concerned, it would treat the multiple PEs
that it is connected to as the same switch. This allows the CE to
aggregate links that are attached to different PEs in the same
bundle.
This mechanism could be used only if it produces ESIs that satisfy
the uniqueness requirement specified above.
* Type 2 (T=0x02) - This type is used in the case of indirectly
connected hosts via a bridged LAN between the CEs and the PEs.
The ESI Value is auto-generated and determined based on the Layer
2 bridge protocol as follows: If the Multiple Spanning Tree
Protocol (MSTP) is used in the bridged LAN, then the value of the
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ESI is derived by listening to Bridge PDUs (BPDUs) on the Ethernet
segment. To achieve this, the PE is not required to run MSTP.
However, the PE must learn the Root Bridge MAC address and Bridge
Priority of the root of the Internal Spanning Tree (IST) by
listening to the BPDUs. The ESI Value is constructed as follows:
- Root Bridge MAC address (6 octets). The Root Bridge MAC
address MUST be encoded in the high-order 6 octets of the ESI
Value field.
- Root Bridge Priority (2 octets). The CE Root Bridge Priority
MUST be encoded in the 2 octets next to the Root Bridge MAC
address.
- The remaining octet SHOULD be set to 0x00.
This mechanism could be used only if it produces ESIs that satisfy
the uniqueness requirement specified above.
* Type 3 (T=0x03) - This type indicates a MAC-based ESI Value that
can be auto-generated or configured by the operator. The ESI
Value is constructed as follows:
- System MAC address (6 octets). The PE MAC address MUST be
encoded in the high-order 6 octets of the ESI Value field.
- Local Discriminator value (3 octets). The Local Discriminator
value MUST be encoded in the low-order 3 octets of the ESI
Value.
This mechanism could be used only if it produces ESIs that satisfy
the uniqueness requirement specified above.
* Type 4 (T=0x04) - This type indicates a router-ID ESI Value that
can be auto-generated or configured by the operator. The ESI
Value is constructed as follows:
- Router ID (4 octets). The system router ID MUST be encoded in
the high-order 4 octets of the ESI Value field.
- Local Discriminator value (4 octets). The Local Discriminator
value MUST be encoded in the 4 octets next to the IP address.
- The low-order octet of the ESI Value SHOULD be set to 0x00.
This mechanism could be used only if it produces ESIs that satisfy
the uniqueness requirement specified above.
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* Type 5 (T=0x05) - This type indicates an Autonomous System
(AS)-based ESI Value that can be auto-generated or configured by
the operator. The ESI Value is constructed as follows:
- AS number (4 octets). This is an AS number owned by the system
and MUST be encoded in the high-order 4 octets of the ESI Value
field. If a 2-octet AS number is used, the high-order extra
octets will be 0x0000.
- Local Discriminator value (4 octets). The Local Discriminator
value MUST be encoded in the 4 octets next to the AS number.
- The low-order octet of the ESI Value will be set to 0x00.
This mechanism could be used only if it produces ESIs that satisfy
the uniqueness requirement specified above.
Note that a CE always sends packets belonging to a specific flow
using a single link towards a PE. For instance, if the CE is a host,
then, as mentioned earlier, the host treats the multiple links that
it uses to reach the PEs as a Link Aggregation Group (LAG). The CE
employs a local hashing function to map traffic flows onto links in
the LAG.
If a bridged network is multihomed to more than one PE in an EVPN
network via switches, then the support of All-Active redundancy mode
requires the bridged network to be connected to two or more PEs using
a LAG.
If a bridged network does not connect to the PEs using a LAG, then
only one of the links between the bridged network and the PEs must be
the active link for a given <ES, EVI>. In this case, the set of
Ethernet A-D per ES routes advertised by each PE MUST have the
"Single-Active" bit in the flags of the ESI Label extended community
set to 1.
6. Ethernet Tag ID
An Ethernet Tag ID is a 32-bit field containing either a 12-bit or
24-bit identifier that identifies a particular broadcast domain
(e.g., a VLAN) in an EVPN instance. The 12-bit identifier is called
the VLAN ID (VID). An EVPN instance consists of one or more
broadcast domains (one or more VLANs). VLANs are assigned to a given
EVPN instance by the provider of the EVPN service. A given VLAN can
itself be represented by multiple VIDs. In such cases, the PEs
participating in that VLAN for a given EVPN instance are responsible
for performing VLAN ID translation to/from locally attached CE
devices.
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The following subsections discuss the relationship between broadcast
domains (e.g., VLANs), Ethernet Tag IDs (e.g., VIDs), and MAC-VRFs as
well as the setting of the Ethernet Tag ID, in the various EVPN BGP
routes (defined in Section 8), for the different types of service
interfaces described in [RFC7209].
The following Ethernet Tag ID value is reserved:
* Ethernet Tag ID {0xFFFFFFFF} is known as MAX-ET.
6.1. VLAN-Based Service Interface
With this service interface, an EVPN instance consists of only a
single broadcast domain (e.g., a single VLAN). Therefore, there is a
one-to-one mapping between a VID on this interface and a MAC-VRF.
Since a MAC-VRF corresponds to a single VLAN, it consists of a single
bridge table corresponding to that VLAN. If the VLAN is represented
by multiple VIDs (e.g., a different VID per Ethernet segment per PE),
then each PE needs to perform VID translation for frames destined to
its Ethernet segment(s). In such scenarios, the Ethernet frames
transported over an MPLS/IP network SHOULD remain tagged with the
originating VID, and a VID translation MUST be supported in the data
path and MUST be performed on the disposition PE. The Ethernet Tag
ID in all EVPN routes MUST be set to 0.
6.2. VLAN Bundle Service Interface
With this service interface, an EVPN instance corresponds to multiple
broadcast domains (e.g., multiple VLANs); however, only a single
bridge table is maintained per MAC-VRF, which means multiple VLANs
share the same bridge table. This implies that MAC addresses MUST be
unique across all VLANs for that EVI in order for this service to
work. In other words, there is a many-to-one mapping between VLANs
and a MAC-VRF, and the MAC-VRF consists of a single bridge table.
Furthermore, a single VLAN must be represented by a single VID --
e.g., no VID translation is allowed for this service interface type.
The MPLS-encapsulated frames MUST remain tagged with the originating
VID. Tag translation is NOT permitted. The Ethernet Tag ID in all
EVPN routes MUST be set to 0.
6.2.1. Port-Based Service Interface
This service interface is a special case of the VLAN bundle service
interface, where all of the VLANs on the port are part of the same
service and map to the same bundle. The procedures are identical to
those described in Section 6.2.
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6.3. VLAN-Aware Bundle Service Interface
With this service interface, an EVPN instance consists of multiple
broadcast domains (e.g., multiple VLANs) with each VLAN having its
own bridge table -- i.e., multiple bridge tables (one per VLAN) are
maintained by a single MAC-VRF corresponding to the EVPN instance.
Broadcast, unknown unicast, or multicast (BUM) traffic is sent only
to the CEs in a given broadcast domain; however, the broadcast
domains within an EVI either MAY each have their own P-Tunnel or MAY
share P-Tunnels -- e.g., all of the broadcast domains in an EVI MAY
share a single P-Tunnel.
In the case where a single VLAN is represented by a single VID and
thus no VID translation is required for the operational duration of
that VLAN , an MPLS-encapsulated packet MUST carry that VID and the
Ethernet Tag ID in all EVPN routes advertised for this BD MUST be set
to that VID. The advertising PE SHOULD advertise the MPLS Label in
the Ethernet A-D per EVI and Inclusive Multicast routes and MPLS
Label1 in the MAC/IP Advertisement routes representing both the
Ethernet Tag ID and the EVI but MAY advertise the labels representing
ONLY the EVI. This decision is only a local matter by the
advertising PE which is also the disposition PE) and doesn't affect
any other PEs.
In the case where a single VLAN is represented by different VIDs on
different CEs and thus VID translation is required, a normalized
Ethernet Tag ID (VID) (i.e., a unique network-wide VID in context of
the EVI) MUST be carried in the EVPN BGP routes. Furthermore, the
advertising PE SHOULD advertise the MPLS Label in the Ethernet A-D
per EVI and Inclusive Multicast routes and MPLS Label1 in the MAC/IP
Advertisement routes representing both the Ethernet Tag ID and the
EVI, so that upon receiving an MPLS-encapsulated packet, the
advertising PE can identify the corresponding bridge table from the
MPLS EVPN label and perform Ethernet Tag ID translation ONLY at the
disposition PE -- i.e., the Ethernet frames transported over the
MPLS/IP network MUST remain tagged with the originating VID, and VID
translation is performed on the disposition PE. The Ethernet Tag ID
in all EVPN routes MUST be set to the normalized Ethernet Tag ID
assigned by the EVPN provider.
6.3.1. Port-Based VLAN-Aware Service Interface
This service interface is a special case of the VLAN-aware bundle
service interface, where all of the VLANs on the port are part of the
same service and are mapped to a single bundle but without any VID
translation. The procedures are a subset of those described in
Section 6.3.
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6.4. EVPN PE Model
Since this document discusses EVPN operation in relationship to MAC-
VRF, EVI, Broadcast Domain (BD), and Bridge Table (BT), it is
important to understand the relationship between these terms.
Therefore, the following PE model is depicted below to illustrate the
relationship among them.
+--------------------------------------------------+
| |
| +------------------+ EVPN PE |
| Attachment | +------------------+ |
| Circuit(AC1) | | +----------+ | MPLS/NVO tunnel
----------------------*Bridge | | +-----
| | | |Table(BT1)| | / \ \
| | | | |<------------------> |Eth|
| | | | VLAN x | | \ / /
| | | +----------+ | +-----
| | | ... | |
| | | +----------+ | MPLS/NVO tunnel
| | | |Bridge | | +-----
| | | |Table(BT2)| | / \ \
| | | | |<------------------> |Eth|
----------------------* VLAN y | | \ / /
| AC2 | | +----------+ | +-----
| | | MAC-VRF1 | |
| +-+ RD1/RT1 | |
| +------------------+ |
| |
| |
+---------------------------------------------------+
Figure 1: EVPN PE Model
A tenant configured for an EVPN service instance (i.e, EVI) on a PE,
is instantiated by a single MAC Virtual Routing and Forwarding table
(MAC-VRF) on that PE. A MAC-VRF consists of one or more Bridge
Tables (BTs) where each BT corresponds to a VLAN (broadcast domain -
BD). If a service interface for an EVPN PE is configured in VLAN-
based mode (i.e., Section 6.1), then there is only a single BT per
MAC-VRF (per EVI) - i.e., there is only one tenant VLAN per EVI.
However, if a service interface for an EVPN PE is configured in VLAN-
Aware Bundle mode (i.e., Section 6.3), then there are several BTs per
MAC-VRF (per EVI) - i.e., there are several tenant VLANs per EVI.
The relationship among these terms can be summarized as follow:
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* An EVI consists of one or more BDs and a MAC-VRF consists of one
or more BTs, one for each BD. A BD is identified by an Ethernet
Tag ID which is typically represented by a single VLAN ID (VID);
however, it can be represented by multiple VIDs (i.e., Shared VLAN
Learning (SVL) mode in 802.1Q).
* In VLAN-based mode, there is one EVI per VLAN and thus one BD/BT
per VLAN. Furthermore, there is one BT per MAC-VRF.
* In VLAN-bundle mode, which can be considered as analogous to SVL
mode in 802.1Q, there is one BD per EVI and one BT per MAC-VRF
with multiple VIDs representing that BD.
* In VLAN-aware bundle mode, there is one EVI with multiple BDs
where each BD is represented by a VLAN. Furthermore, there are
multiple BTs in a single MAC-VRF.
A single tenant subnet is typically represented by a VLAN and thus
supported by a single BT. For a given tenant there are as many BTs
as there are subnets as shown in the PE model above.
MAC-VRF is identified by its corresponding route target and route
distinguisher. If operating in EVPN VLAN-based mode, then a
receiving PE that receives an EVPN route with MAC-VRF route target
can identify the corresponding BT; however, if operating in EVPN
VLAN-ware bundle mode, then the receiving PE needs both the MAC-VRF
route target and Ethernet Tag ID in order to identify the
corresponding BT.
7. BGP EVPN Routes
This document defines a new BGP Network Layer Reachability
Information (NLRI) called the EVPN NLRI.
The format of the EVPN NLRI is as follows:
+-----------------------------------+
| Route Type (1 octet) |
+-----------------------------------+
| Length (1 octet) |
+-----------------------------------+
| Route Type specific (variable) |
+-----------------------------------+
The Route Type field defines the encoding of the rest of the EVPN
NLRI (Route Type specific EVPN NLRI).
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The Length field indicates the length in octets of the Route Type
specific field of the EVPN NLRI.
This document defines the following Route Types:
+ 1 - Ethernet Auto-Discovery (A-D) route
+ 2 - MAC/IP Advertisement route
+ 3 - Inclusive Multicast Ethernet Tag route
+ 4 - Ethernet Segment route
The detailed encoding and procedures for these route types are
described in subsequent sections.
The EVPN NLRI is carried in BGP [RFC4271] using BGP Multiprotocol
Extensions [RFC4760] with an Address Family Identifier (AFI) of 25
(L2VPN) and a Subsequent Address Family Identifier (SAFI) of 70
(EVPN). The NLRI field in the MP_REACH_NLRI/MP_UNREACH_NLRI
attribute contains the EVPN NLRI (encoded as specified above).
In order for two BGP speakers to exchange labeled EVPN NLRI, they
must use BGP Capabilities Advertisements to ensure that they both are
capable of properly processing such NLRI. This is done as specified
in [RFC4760], by using capability code 1 (multiprotocol BGP) with an
AFI of 25 (L2VPN) and a SAFI of 70 (EVPN).
For the purpose of BGP route key processing, a BGP route consists of
RD + Prefix. For the remainder of this document, whenever BGP route
key processing for "the prefix" is mentioned, it means the prefix
part of the BGP route.
7.1. Ethernet Auto-Discovery Route
An Ethernet A-D route type specific EVPN NLRI consists of the
following:
+---------------------------------------+
| Route Distinguisher (RD) (8 octets) |
+---------------------------------------+
|Ethernet Segment Identifier (10 octets)|
+---------------------------------------+
| Ethernet Tag ID (4 octets) |
+---------------------------------------+
| MPLS Label (3 octets) |
+---------------------------------------+
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For the purpose of BGP route key processing, only the Ethernet
Segment Identifier and the Ethernet Tag ID are considered to be part
of the prefix in the NLRI. The MPLS Label field is to be treated as
a route attribute as opposed to being part of the route.
The MPLS Label field is encoded as 3 octets, where the high-order
20 bits contain the label value.
For procedures and usage of this route, please see Sections 8.2
("Fast Convergence") and 8.4 ("Aliasing and Backup Path").
7.2. MAC/IP Advertisement Route
A MAC/IP Advertisement route type specific EVPN NLRI consists of the
following:
+---------------------------------------+
| RD (8 octets) |
+---------------------------------------+
|Ethernet Segment Identifier (10 octets)|
+---------------------------------------+
| Ethernet Tag ID (4 octets) |
+---------------------------------------+
| MAC Address Length (1 octet) |
+---------------------------------------+
| MAC Address (6 octets) |
+---------------------------------------+
| IP Address Length (1 octet) |
+---------------------------------------+
| IP Address (0, 4, or 16 octets) |
+---------------------------------------+
| MPLS Label1 (3 octets) |
+---------------------------------------+
| MPLS Label2 (0 or 3 octets) |
+---------------------------------------+
For the purpose of BGP route key processing, only the Ethernet Tag
ID, MAC Address Length, MAC Address, IP Address Length, and IP
Address fields are considered to be part of the prefix in the NLRI.
The Ethernet Segment Identifier, MPLS Label1, and MPLS Label2 fields
are to be treated as route attributes as opposed to being part of the
"route". Both the IP and MAC address lengths are expressed in bits.
The MPLS Label1 and MPLS Label2 fields are encoded as 3 octets, where
the high-order 20 bits contain the label value.
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For procedures and usage of this route, please see Sections 9
("Determining Reachability to Unicast MAC Addresses") and 14 ("Load
Balancing of Unicast Packets").
7.3. Inclusive Multicast Ethernet Tag Route
An Inclusive Multicast Ethernet Tag route type specific EVPN NLRI
consists of the following:
+---------------------------------------+
| RD (8 octets) |
+---------------------------------------+
| Ethernet Tag ID (4 octets) |
+---------------------------------------+
| IP Address Length (1 octet) |
+---------------------------------------+
| Originating Router's IP Address |
| (4 or 16 octets) |
+---------------------------------------+
The IP address length is in bits. For the purpose of BGP route key
processing, only the Ethernet Tag ID, IP Address Length, and
Originating Router's IP Address fields are considered to be part of
the prefix in the NLRI.
For procedures and usage of this route, please see Sections 11
("Handling of Multi-destination Traffic"), 12 ("Processing of Unknown
Unicast Packets"), and 16 ("Multicast and Broadcast").
7.4. Ethernet Segment Route
An Ethernet Segment route type specific EVPN NLRI consists of the
following:
+---------------------------------------+
| RD (8 octets) |
+---------------------------------------+
|Ethernet Segment Identifier (10 octets)|
+---------------------------------------+
| IP Address Length (1 octet) |
+---------------------------------------+
| Originating Router's IP Address |
| (4 or 16 octets) |
+---------------------------------------+
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The IP address length is in bits. For the purpose of BGP route key
processing, only the Ethernet Segment ID, IP Address Length, and
Originating Router's IP Address fields are considered to be part of
the prefix in the NLRI.
For procedures and usage of this route, please see Section 8.5
("Designated Forwarder Election").
7.5. ESI Label Extended Community
This Extended Community is a transitive Extended Community having a
Type field value of 0x06 and the Sub-Type 0x01. It may be advertised
along with Ethernet Auto-discovery routes, and it enables split-
horizon procedures for multihomed sites as described in Section 8.3
("Split Horizon"). The ESI Label field represents an ES by the
advertising PE, and it is used in split-horizon filtering by other
PEs that are connected to the same multihomed Ethernet segment.
The ESI Label field is encoded as 3 octets, where the high-order
20 bits contain the label value.
The ESI label value MAY be zero if no split-horizon filtering
procedures are required in any of the VLANs of the Ethernet Segment.
This is the case in [RFC8214] or Ethernet Segments using Local Bias
procedures in [I-D.ietf-bess-evpn-mh-split-horizon].
Each ESI Label extended community is encoded as an 8-octet value, as
follows:
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=0x06 | Sub-Type=0x01 | Flags(1 octet)| Reserved=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved=0 | ESI Label (3 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This document creates an IANA registry called "EVPN ESI Multihoming
Attributes" (Section 21 for the Flags octet, where the following
field "Multihomed site redundancy mode (RED)" field is defined with
initial bit allocations:
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0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| MBZ |RED| (MBZ = MUST Be Zero)
+-+-+-+-+-+-+-+-+
Name Meaning
---------------------------------------------------------------
RED Multihomed site redundancy mode
Multihomed site redundancy mode:
RED = 00: A value of 00 means that the multihomed site is operating
in All-Active redundancy mode.
RED = 01: A value of 01 means that the multihomed site is operating
in Single-Active redundancy mode.
7.6. ES-Import Route Target
This is a transitive Route Target extended community carried with the
Ethernet Segment route, having a Type field value of 0x06 and the
Sub-Type 0x02. When used, it enables all the PEs connected to the
same multihomed site to import the Ethernet Segment routes.
* The value MAY be derived automatically for ESI Type 0 by encoding
the high-order 6-octet portion of the 9-octet ESI Value, which
corresponds to part of the arbitrary value configured, in the ES-
Import Route Target.
* The value is derived automatically for ESI Types 1, 2, and 3, by
encoding the high-order 6-octet portion of the 9-octet ESI Value,
which corresponds to a MAC address, in the ES-Import Route Target.
* The value MAY be derived automatically for ESI Types 4 and 5, by
encoding the high-order 6-octet portion of the 9-octet ESI Value,
which corresponds to a Router ID or AS number (4-octets)
respectively, and 2-octets of Local Discriminator, in the
ES-Import Route Target.
The format of this Extended Community is as follows:
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=0x06 | Sub-Type=0x02 | ES-Import ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ES-Import Cont'd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This document expands the definition of the Route Target extended
community to allow the value of the high-order octet (Type field) to
be 0x06 (in addition to the values specified in [RFC4360]). The
low-order octet (Sub-Type field) value 0x02 indicates that this
Extended Community is of type "Route Target". The Type field value
0x06 indicates that the structure of this RT is a 6-octet value
(e.g., a MAC address). A BGP speaker that implements RT Constraint
[RFC4684] MUST apply the RT Constraint procedures to the ES-Import RT
as well.
For procedures and usage of this extended community, please see
Section 8.1 ("Multihomed Ethernet Segment Auto-discovery").
7.7. MAC Mobility Extended Community
This Extended Community is a transitive Extended Community having a
Type field value of 0x06 and the Sub-Type 0x00. It may be advertised
along with MAC/IP Advertisement routes. The procedures for using
this extended community are described in Section 15 ("MAC Mobility").
The MAC Mobility extended community is encoded as an 8-octet value,
as follows:
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=0x06 | Sub-Type=0x00 |Flags(1 octet)| Reserved=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The low-order bit of the Flags octet is defined as the
"Sticky/static" flag and may be set to 1. A value of 1 means that
the MAC address is static and cannot move. The sequence number is
used to ensure that PEs retain the correct MAC/IP Advertisement route
when multiple updates occur for the same MAC address.
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7.8. Default Gateway Extended Community
The Default Gateway community is an Extended Community of an Opaque
Type (see Section 3.3 of [RFC4360]). It is a transitive community,
which means that the first octet (Type) is 0x03. The value of the
second octet (Sub-Type) is 0x0d (Default Gateway) as assigned by
IANA. The Value field of this community is reserved (set to 0 by the
senders, ignored by the receivers).
The format of this Extended Community is as follows:
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=0x03 | Sub-Type=0x0d | Reserved=0 ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Reserved=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
For procedures and usage of this extended community, please see
Section 10.1 ("Default Gateway").
7.9. Route Distinguisher Assignment per MAC-VRF
The Route Distinguisher MUST be set to the RD of the MAC-VRF that is
advertising the NLRI. An RD MUST be assigned for a given MAC-VRF on
a PE. This RD MUST be unique across all MAC-VRFs on a PE. It is
RECOMMENDED to use the Type 1 RD [RFC4364]. The value field
comprises an IP address of the PE (typically, the loopback address)
followed by a number unique to the PE. This number may be generated
by the PE. In case of VLAN-based or VLAN Bundle services, this
number may also be generated out of the Ethernet Tag ID for the BD as
long as the value does not exceed a length of 16 bits. Or, in the
Unique VLAN EVPN case, the low-order 12 bits may be the 12-bit VLAN
ID, with the remaining high-order 4 bits set to 0.
7.10. Route Targets
The EVPN route MAY carry one or more Route Target (RT) extended
communities. RTs may be configured (as in IP VPNs) or may be derived
automatically.
If a PE uses RT Constraint, the PE advertises all such RTs using RT
Constraints per [RFC4684]. The use of RT Constraints allows each
EVPN route to reach only those PEs that are configured to import at
least one RT from the set of RTs carried in the EVPN route.
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7.10.1. Auto-derivation from the Ethernet Tag (VLAN ID)
For the "Unique VLAN EVPN" scenario (Section 4), it is highly
desirable to auto-derive the RT from the Ethernet Tag (VLAN ID). The
procedure for performing such auto-derivation is as follows:
* The Global Administrator field of the RT MUST be set to the
Autonomous System (AS) number with which the PE is associated.
* The 12-bit VLAN ID MUST be encoded in the lowest 12 bits of the
Local Administrator field, with the remaining bits set to zero.
For VLAN-based and VLAN Bundle services, the RT may also be auto-
derived as per the above rules but replacing the 12-bit VLAN ID with
a 16-bit Ethernet Tag ID configured for the BD. If the Ethernet Tag
ID length is 24 bits, the RT for the MAC-VRF can be auto-derived as
per [RFC8365] section 5.1.2.1.
7.11. EVPN Layer 2 Attributes Extended Community
[RFC8214] defines and requires this extended community ("L2-Attr"),
to be included with per-EVI Ethernet A-D routes when multihoming is
enabled.
Usage and applicability of this Extended community to Bridging is
clarified here.
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ |RSV|RSV|F|C|P|B| (MBZ = MUST Be Zero)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The following bits in Control Flags are defined in [RFC8214]:
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Name Meaning
---------------------------------------------------------------
P If set to 1 in multihoming Single-Active scenarios,
this flag indicates that the advertising PE is the
primary PE. MUST be set to 1 for multihoming
All-Active scenarios by all active PE(s).
B If set to 1 in multihoming Single-Active scenarios,
this flag indicates that the advertising PE is the
backup PE.
C If set to 1, a control word [RFC4448] MUST be present
when sending EVPN packets to this PE. It is
recommended that the control word be included in the
absence of an entropy label [RFC6790].
The bits in Control Flags are extended, and [RFC8214] updated, by the
following additional bits:
Name Meaning
---------------------------------------------------------------
F If set to 1, a Flow Label MUST be present
when sending EVPN packets to this PE.
If set to 0, a Flow Label MUST NOT be present
when sending EVPN packets to this PE.
For procedures and usage of this extended community, with respect to
Control Word and Flow Label, please see Section 18. ("Frame
Ordering").
For procedures and usage of this extended community, with respect to
Primary-Backup bits, please see Section 8.5. ("Designated Forwarder
Election").
7.11.1. EVPN Layer 2 Attributes Partitioning
The information carried in the L2-Attr Extended Community may be ESI
and EVI-specific, or only EVI-specific. In order to minimize the
processing overhead of configuration-time items, such as MTU not
expected to change at runtime based on failures, the L2-Attr Extended
Community, specified in [RFC8214], is partitioned and a subset of
information is carried over each Ethernet A-D per EVI and Inclusive
Multicast routes.
The EVPN L2-Attr Extended Community, when added to Inclusive
Multicast route:
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* per-EVI attributes MTU, Control Word and Flow Label are conveyed,
and;
* per-ESI-and-EVI attributes P, B MUST be zero.
+-------------------------------------------+
| Type (0x06) / Sub-type (0x04) (2 octets) |
+-------------------------------------------+
| Control Flags (2 octets) |
+-------------------------------------------+
| L2 MTU (2 octets) |
+-------------------------------------------+
| Reserved (2 octets) |
+-------------------------------------------+
1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ | MBZ |F|C|MBZ| (MBZ = MUST Be Zero)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The EVPN L2-Attr Extended Community is included on Ethernet A-D per
EVI route and:
* per-ESI-and-EVI attributes P, B are conveyed, and;
* per-EVI attributes MTU, Control Word and Flow Label MUST be zero.
+-------------------------------------------+
| Type (0x06) / Sub-type (0x04) (2 octets) |
+-------------------------------------------+
| Control Flags (2 octets) |
+-------------------------------------------+
| MBZ (2 octets) |
+-------------------------------------------+
| Reserved (2 octets) |
+-------------------------------------------+
1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ | MBZ |P|B| (MBZ = MUST Be Zero)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Note that in both of the above cases, the values conveyed in this
extended community are at the granularity of an individual EVI (or
<EVI, BD> for VLAN-aware bundle) and hence may vary for different
EVIs.
As described in Section 8.4, support of Ethernet A-D per EVI route is
OPTIONAL. However, this route is MANDATORY when sending the L2-Attr
Extended Community and its per-ESI-and-EVI attributes.
7.11.2. EVPN Layer 2 Attributes Negotiation
EVPN Layer 2 attributes received in remote routes are checked for
consistency and interoperability against local values, as also
described in Section 3.1 of [RFC8214]. Mismatches SHOULD be notified
to the operator.
A received L2 MTU of zero means that no MTU checking against the
local MTU is needed. A received non-zero MTU from a remote PE MUST
be checked against the local MTU, and if there is a mismatch, the
local PE MUST NOT add the remote PE as the EVPN destination for any
of the corresponding service instances.
When the L2-Attr Extended Community is received from a remote PE, the
control word C flag MUST be checked against local control word
enablement. If there is a mismatch, the local PE MUST NOT add the
remote PE as the EVPN destination for any of the corresponding
service instances.
When the L2-Attr Extended Community is received from a remote PE,
flow label F flag MUST be checked against local flow label
enablement. If there is a mismatch, the local PE MUST NOT add the
remote PE as the EVPN destination for any of the corresponding
service instances. The Flow label capability signaling is further
described in Section 18.1.
7.12. Route Prioritization
In order to achieve the fast convergence referred to in Section 8.2,
BGP speakers SHOULD prioritise advertisement, processing and
redistribution of routes based on relative scale of priority vs.
expected or average scale.
1. Ethernet A-D per ES (Mass-Withdraw Route Type 1) and Ethernet
Segment (Route Type 4) are lower scale, highly convergence
affecting and SHOULD be handled in first order of priority.
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2. Ethernet A-D per EVI, Inclusive Multicast Ethernet Tag route, and
IP Prefix route, as defined in [RFC9136], are sent for each
Bridge or AC at medium scale, may be convergence affecting and
SHOULD be handled in second order of priority.
3. Very highly scalable routes, such as MAC advertisement routes
(zero and non-zero IP portion), Multicast Join Sync and Multicast
Leave Sync routes, as defined in [RFC9251], are considered
'individual routes' and SHOULD be handled in the last order of
priority.
7.13. Best Path Selection
When two (or more) EVPN routes with the same route key (and same or
different RDs) are received, a best path selection algorithm is used
to select and install only one route. The following section
describes best path selection for EVPN routes
The wording is based on the bgp best path selection in [RFC4271]
(BGP) but applied to EVPN routes, attributes and extended communities
and in particular the gateway, static bit, sequence number and
protection flags of Section 7.7, Section 7.8 and Section 7.11 where
applicable.
It is not intended to specify any particular implementation, and
implementations MAY use any algorithm which SHOULD produce the same
selection as the result of the rules that follow.
The tie-breaking algorithm begins by considering all equally
preferable EVPN routes to the same destination, and then selects
routes to be removed from consideration. The algorithm terminates as
soon as only one route remains in consideration.
7.13.1. Best Path Selection for MAC/IP Advertisement routes
This section summarizes the best path selection for MAC/IP
Advertisement routes. The criteria MUST be applied in the order
specified.
1. If at least one of the candidate routes was received with the
Default Gateway extended community, remove from consideration the
routes without the Default Gateway extended community.
Refer to Section 10.1 for more information on the Default Gateway
extended community.
2. If two or more candidate routes contain the Default Gateway
extended community, remove from consideration the routes that are
not local to the PE.
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3. If at least one of the candidate routes was received with the
Static bit set in the MAC Mobility extended community, remove
from consideration the routes without the Static bit set.
Note that this rule does not apply to routes with the Default
Gateway extended community, and the selection process skips this
step for any 2 or more routes after (2) above.
4. If, amongst the candidate routes received, at least one was
received with a highest sequence number in the MAC Mobility
extended community, remove from consideration the routes not tied
for highest sequence number.
Note that this rule does not apply to routes with the Default
Gateway extended community, and the selection process skips this
step for any 2 or more routes after (2) above.
5. If, amongst the candidate routes received, at least one was
received with a higher degree of preference, remove from
consideration the routes not tied for higher degree of
preference, as defined in Section 9.1.1 of [RFC4271].
6. If the steps above do not produce a single route, the rest of the
rules in [RFC4271] apply.
The above selection criteria is followed irrespective of the ESI
value in the routes. EVPN Multi-Homing procedures for Aliasing or
Backup paths in Section 8.4 are applied to the selected MAC/IP
Advertisement route.
If Steps 1-2 leave Equal Cost Multi-Paths (ECMP) among multiple MAC/
IP Advertisement routes with the Default Gateway extended community,
and ECMP is enabled by policy, then multiple paths MAY be used to
reach a given MAC/IP Advertisement route.
7.13.2. Best Path Selection for Ethernet A-D per EVI routes
This section summarizes the best path selection for Ethernet A-D per
EVI routes routes. The criteria MUST be applied in the order
specified.
1. For non-zero ESI routes, the EVPN Multi-Homing procedures in
[RFC8214] and Section 8.4 of this document for Aliasing and
Backup path are followed:
1. If at least one of the candidate routes was received with the
EVPN Layer 2 Attributes extended community, remove from
consideration the routes without the EVPN Layer 2 Attributes
extended community.
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2. P and B flags are considered for the selection of the routes
when sending traffic to a remote Ethernet Segment.
Note that this rule does not apply to routes with ESI 0, and the
selection process skips this step.
2. If more than one candidate routes remain for each remote PE (ESI
0 or attached to the same ES) steps 4-5 in Section 7.13.1 are
followed.
7.13.3. Best Path Selection for Inclusive Multicast Ethernet Tag routes
This section summarizes the best path selection for Inclusive
Multicast routes. The algorithm is the same as in step 5 of
Section 7.13.1, and the criteria MUST be applied in the order
specified.
8. Multihoming Functions
This section discusses the functions, procedures, and associated BGP
routes used to support multihoming in EVPN. This covers both
multihomed device (MHD) and multihomed network (MHN) scenarios.
8.1. Multihomed Ethernet Segment Auto-discovery
PEs connected to the same Ethernet segment can automatically discover
each other with minimal to no configuration through the exchange of
the Ethernet Segment route.
8.1.1. Constructing the Ethernet Segment Route
The Route Distinguisher MUST be a Type 1 RD [RFC4364]. The value
field comprises an IP address of the PE (typically, the loopback
address) followed by a number unique to the PE.
The Ethernet Segment Identifier (ESI) MUST be set to the 10-octet
value described in Section 5.
The BGP advertisement that advertises the Ethernet Segment route MUST
also carry an ES-Import Route Target, as defined in Section 7.6.
The Ethernet Segment route filtering MUST be done such that the
Ethernet Segment route is imported only by the PEs that are
multihomed to the same Ethernet segment. To that end, each PE that
is connected to a particular Ethernet segment constructs an import
filtering rule to import a route that carries the ES-Import Route
Target, constructed from the ESI.
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8.2. Fast Convergence
In EVPN, MAC address reachability is learned via the BGP control
plane over the MPLS network. As such, in the absence of any fast
protection mechanism, the network convergence time is a function of
the number of MAC/IP Advertisement routes that must be withdrawn by
the PE encountering a failure. For highly scaled environments, this
scheme yields slow convergence.
To alleviate this, EVPN defines a mechanism to efficiently and
quickly signal, to remote PE nodes, the need to update their
forwarding tables upon the occurrence of a failure in connectivity to
an Ethernet segment. This is done by having each PE advertise a set
of one or more Ethernet A-D per ES routes for each locally attached
Ethernet segment (refer to Section 8.2.1 below for details on how
these routes are constructed). A PE may need to advertise more than
one Ethernet A-D per ES route for a given ES because the ES may be in
a multiplicity of EVIs and the RTs for all of these EVIs may not fit
into a single route. Advertising a set of Ethernet A-D per ES routes
for the ES allows each route to contain a subset of the complete set
of RTs. Each Ethernet A-D per ES route is differentiated from the
other routes in the set by a different Route Distinguisher.
Upon a failure in connectivity to the attached segment, the PE
withdraws the corresponding set of Ethernet A-D per ES routes. This
triggers all PEs that receive the withdrawal to update their next-hop
adjacencies for all MAC addresses associated with the Ethernet
segment in question. If no other PE had advertised an Ethernet A-D
per ES route for the same segment, then the PE that received the
withdrawal simply invalidates the MAC entries for that segment.
Otherwise, the PE updates its next-hop adjacencies accordingly.
8.2.1. Constructing Ethernet A-D per Ethernet Segment Route
This section describes the procedures used to construct the Ethernet
A-D per ES route, which is used for fast convergence as discussed
above and for advertising the ESI label used for split-horizon
filtering (as discussed in Section 8.3). Support of this route is
REQUIRED.
The Route Distinguisher MUST be a Type 1 RD [RFC4364]. The value
field comprises an IP address of the PE (typically, the loopback
address) followed by a number unique to the PE.
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The Ethernet Segment Identifier MUST be a 10-octet entity as
described in Section 5 ("Ethernet Segment"). The Ethernet A-D route
is not needed when the Segment Identifier is set to 0 (e.g., single-
homed scenarios). An exception to this rule is described in
[RFC8317].
The Ethernet Tag ID MUST be set to MAX-ET.
The MPLS label in the NLRI MUST be set to 0.
The ESI Label extended community MUST be included in the route. If
All-Active redundancy mode is desired, then the "Single-Active" bit
in the flags of the ESI Label extended community MUST be set to 0 and
the MPLS label in that Extended Community MUST be set to a valid MPLS
label value. The MPLS label in this Extended Community is referred
to as the ESI label and MUST have the same value in each Ethernet A-D
per ES route advertised for the ES. This label MUST be a downstream
assigned MPLS label if the advertising PE is using ingress
replication for receiving multicast, broadcast, or unknown unicast
traffic from other PEs. If the advertising PE is using P2MP MPLS
LSPs for sending multicast, broadcast, or unknown unicast traffic,
then this label MUST be an upstream assigned MPLS label, unless DCB
allocated labels are used. The usage of this label is described in
Section 8.3.
If Single-Active redundancy mode is desired, then the "Single-Active"
bit in the flags of the ESI Label extended community MUST be set to 1
and the ESI label SHOULD be set to a valid MPLS label value.
8.2.1.1. Ethernet A-D Route Targets
Each Ethernet A-D per ES route MUST carry one or more Route Target
(RT) extended communities. The set of Ethernet A-D routes per ES
MUST carry the entire set of RTs for all the EVPN instances to which
the Ethernet segment belongs.
8.3. Split Horizon
Consider a CE that is multihomed to two or more PEs on an Ethernet
segment ES1 operating in All-Active redundancy mode. If the CE sends
a broadcast, unknown unicast, or multicast (BUM) packet to one of the
Non-Designated Forwarder (Non-DF) PEs, say PE1, then PE1 will forward
that packet to all or a subset of the other PEs in that EVPN
instance, including the DF PE for that Ethernet segment. In this
case, the DF PE to which the CE is multihomed MUST drop the packet
and not forward back to the CE. This filtering is referred to as
"split-horizon filtering" in this document.
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When a set of PEs are operating in Single-Active redundancy mode, the
use of this split-horizon filtering mechanism is highly recommended
because it prevents transient loops at the time of failure or
recovery that would impact the Ethernet segment -- e.g., when two PEs
think that both are DFs for that segment before the DF election
procedure settles down.
In order to achieve this split-horizon function, every BUM packet
originating from a Non-DF PE is encapsulated with an MPLS label that
identifies the Ethernet segment of origin (i.e., the segment from
which the frame entered the EVPN network). This label is referred to
as the ESI label and MUST be distributed by all PEs when operating in
All-Active redundancy mode using a set of Ethernet A-D per ES routes,
per Section 8.2.1 above. The ESI label SHOULD be distributed by all
PEs when operating in Single-Active redundancy mode using a set of
Ethernet A-D per ES routes. These routes are imported by the PEs
connected to the Ethernet segment and also by the PEs that have at
least one EVPN instance in common with the Ethernet segment in the
route. As described in Section 8.1.1, the route MUST carry an ESI
Label extended community with a valid ESI label. The disposition PE
relies on the value of the ESI label to determine whether or not a
BUM frame is allowed to egress a specific Ethernet segment.
8.3.1. ESI Label Assignment
The following subsections describe the assignment procedures for the
ESI label, which differ depending on the type of tunnels being used
to deliver multi-destination packets in the EVPN network.
8.3.1.1. Ingress Replication
Each PE that operates in All-Active or Single-Active redundancy mode
and that uses ingress replication to receive BUM traffic advertises a
downstream assigned ESI label in the set of Ethernet A-D per ES
routes for its attached ES. This label MUST be programmed in the
platform label space by the advertising PE, and the forwarding entry
for this label must result in NOT forwarding packets received with
this label onto the Ethernet segment for which the label was
distributed.
The rules for the inclusion of the ESI label in a BUM packet by the
ingress PE operating in All-Active redundancy mode are as follows:
* A Non-DF ingress PE MUST include the ESI label distributed by the
DF egress PE in the copy of a BUM packet sent to it.
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* An ingress PE (DF or Non-DF) SHOULD include the ESI label
distributed by each Non-DF egress PE in the copy of a BUM packet
sent to it.
The rule for the inclusion of the ESI label in a BUM packet by the
ingress PE operating in Single-Active redundancy mode is as follows:
* An ingress DF PE SHOULD include the ESI label distributed by the
egress PE in the copy of a BUM packet sent to it.
In both All-Active and Single-Active redundancy mode, an ingress PE
MUST NOT include an ESI label in the copy of a BUM packet sent to an
egress PE that is not attached to the ES through which the BUM packet
entered the EVI.
As an example, consider PE1 and PE2, which are multihomed to CE1 on
ES1 and operating in All-Active multihoming mode. Further, consider
that PE1 is using P2P or MP2P LSPs to send packets to PE2. Consider
that PE1 is the Non-DF for VLAN1 and PE2 is the DF for VLAN1, and PE1
receives a BUM packet from CE1 on VLAN1 on ES1. In this scenario,
PE2 distributes an Inclusive Multicast Ethernet Tag route for VLAN1
corresponding to an EVPN instance. So, when PE1 sends a BUM packet
that it receives from CE1, it MUST first push onto the MPLS label
stack the ESI label that PE2 has distributed for ES1. It MUST then
push onto the MPLS label stack the MPLS label distributed by PE2 in
the Inclusive Multicast Ethernet Tag route for VLAN1. The resulting
packet is further encapsulated in the P2P or MP2P LSP label stack
required to transmit the packet to PE2. When PE2 receives this
packet, it determines, from the top MPLS label, the set of ESIs to
which it will replicate the packet after any P2P or MP2P LSP labels
have been removed. If the next label is the ESI label assigned by
PE2 for ES1, then PE2 MUST NOT forward the packet onto ES1. If the
next label is an ESI label that has not been assigned by PE2, then
PE2 MUST drop the packet. It should be noted that in this scenario,
if PE2 receives a BUM packet for VLAN1 from CE1, then it SHOULD
encapsulate the packet with an ESI label received from PE1 when
sending it to PE1 in order to avoid any transient loops during a
failure scenario that would impact ES1 (e.g., port or link failure).
8.3.1.2. P2MP MPLS LSPs
The Non-DF PEs that operate in All-Active redundancy mode and that
use P2MP LSPs to send BUM traffic advertise an upstream assigned ESI
label in the set of Ethernet A-D per ES routes for their common
attached ES. This label is upstream assigned by the PE that
advertises the route. This label MUST be programmed by the other PEs
that are connected to the ESI advertised in the route, in the context
label space for the advertising PE. Further, the forwarding entry
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for this label must result in NOT forwarding packets received with
this label onto the Ethernet segment for which the label was
distributed. This label MUST also be programmed by the other PEs
that import the route but are not connected to the ESI advertised in
the route, in the context label space for the advertising PE.
Further, the forwarding entry for this label must be a label pop with
no other associated action.
The DF PE that operates in Single-Active redundancy mode and that
uses P2MP LSPs to send BUM traffic should advertise an upstream
assigned ESI label in the set of Ethernet A-D per ES routes for its
attached ES, just as described in the previous paragraph.
As an example, consider PE1 and PE2, which are multihomed to CE1 on
ES1 and operating in All-Active multihoming mode. Also, consider
that PE3 belongs to one of the EVPN instances of ES1. Further,
assume that PE1, which is the Non-DF, is using P2MP MPLS LSPs to send
BUM packets. When PE1 sends a BUM packet that it receives from CE1,
it MUST first push onto the MPLS label stack the ESI label that it
has assigned for the ESI on which the packet was received. The
resulting packet is further encapsulated in the P2MP MPLS label stack
necessary to transmit the packet to the other PEs. Penultimate hop
popping MUST be disabled on the P2MP LSPs used in the MPLS transport
infrastructure for EVPN. When PE2 receives this packet, it
decapsulates the top MPLS label and forwards the packet using the
context label space determined by the top label. If the next label
is the ESI label assigned by PE1 to ES1, then PE2 MUST NOT forward
the packet onto ES1. When PE3 receives this packet, it decapsulates
the top MPLS label and forwards the packet using the context label
space determined by the top label. If the next label is the ESI
label assigned by PE1 to ES1 and PE3 is not connected to ES1, then
PE3 MUST pop the label and flood the packet over all local ESIs in
that EVPN instance. It should be noted that when PE2 sends a BUM
frame over a P2MP LSP, it should encapsulate the frame with an ESI
label even though it is the DF for that VLAN, in order to avoid any
transient loops during a failure scenario that would impact ES1
(e.g., port or link failure).
8.3.1.3. MP2MP MPLS LSPs
The procedures for MP2MP tunnels follow Section 8.3.1.2, with the
exceptions described in this section.
When MP2MP tunnels are used, ESI Labels MUST be allocated from a DCB
and the same label must be used by all the PEs attached to the same
Ethernet Segment.
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In that way, any egress PE with local Ethernet Segments can identify
the source ES of the received BUM packets.
8.4. Aliasing and Backup Path
In the case where a CE is multihomed to multiple PE nodes, using a
Link Aggregation Group (LAG) with All-Active redundancy, it is
possible that only a single PE learns a set of the MAC addresses
associated with traffic transmitted by the CE. This leads to a
situation where remote PE nodes receive MAC/IP Advertisement routes
for these addresses from a single PE, even though multiple PEs are
connected to the multihomed segment. As a result, the remote PEs are
not able to effectively load balance traffic among the PE nodes
connected to the multihomed Ethernet segment. This could be the
case, for example, when the PEs perform data-plane learning on the
access, and the load-balancing function on the CE hashes traffic from
a given source MAC address to a single PE.
Another scenario where this occurs is when the PEs rely on control-
plane learning on the access (e.g., using ARP), since ARP traffic
will be hashed to a single link in the LAG.
To address this issue, EVPN introduces the concept of 'aliasing',
which is the ability of a PE to signal that it has reachability to an
EVPN instance on a given ES even when it has learned no MAC addresses
from that EVI/ES. The Ethernet A-D per EVI route is used for this
purpose. A remote PE that receives a MAC/IP Advertisement route with
a non-reserved ESI SHOULD consider the advertised MAC address to be
reachable via all PEs that have advertised reachability to that MAC
address's EVI/ES/Ethernet Tag ID via the combination of an Ethernet
A-D per EVI route for that EVI/ES/Ethernet Tag ID AND Ethernet A-D
per ES routes for that ES with the "Single-Active" bit in the flags
of the ESI Label extended community set to 0.
Note that the Ethernet A-D per EVI route may be received by a remote
PE before it receives the set of Ethernet A-D per ES routes.
Therefore, in order to handle corner cases and race conditions, the
Ethernet A-D per EVI route MUST NOT be used for traffic forwarding by
a remote PE until it also receives the associated set of Ethernet A-D
per ES routes.
The backup path is a closely related function, but it is used in
Single-Active redundancy mode. In this case, a PE also advertises
that it has reachability to a given EVI/ES using the same combination
of Ethernet A-D per EVI route and Ethernet A-D per ES route as
discussed above, but with the "Single-Active" bit in the flags of the
ESI Label extended community set to 1. A remote PE that receives a
MAC/IP Advertisement route with a non-reserved ESI SHOULD consider
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the advertised MAC address to be reachable via any PE that has
advertised this combination of Ethernet A-D routes, and it SHOULD
install a backup path for that MAC address.
Please see Section 14.1.1 for a description of the backup paths
operation.
Support of this route is OPTIONAL. However, this route is MANDATORY
when sending the L2-Attr Extended Community and its per-ESI-and-EVI
attributes used in Aliasing and Backup path computations above.
8.4.1. Constructing Ethernet A-D per EVPN Instance Route
This section describes the procedures used to construct the Ethernet
A-D per EVPN instance (EVI) route, which is used for aliasing (as
discussed above).
The Route Distinguisher (RD) MUST be set per Section 7.9.
The Ethernet Segment Identifier MUST be a 10-octet entity as
described in Section 5 ("Ethernet Segment"). The Ethernet A-D route
is not needed when the Segment Identifier is set to 0.
The Ethernet Tag ID is set as defined in Section 6.
Note that the above allows the Ethernet A-D per EVI route to be
advertised with one of the following granularities:
* One Ethernet A-D route per <ESI, Ethernet Tag ID> tuple per
MAC-VRF. This is applicable when the PE uses MPLS-based
disposition with VID translation or may be applicable when the PE
uses MAC-based disposition with VID translation.
* One Ethernet A-D route for each <ESI> per MAC-VRF (where the
Ethernet Tag ID is set to 0). This is applicable when the PE uses
MAC-based disposition or MPLS-based disposition without VID
translation.
The usage of the MPLS label is described in Section 14 ("Load
Balancing of Unicast Packets").
The Next Hop field of the MP_REACH_NLRI attribute of the route MUST
be set to the IPv4 or IPv6 address of the advertising PE.
The Ethernet A-D per EVI route MUST carry one or more Route Target
(RT) extended communities, per Section 7.10.
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8.5. Designated Forwarder Election
Consider a CE that is a host or a router that is multihomed directly
to more than one PE in an EVPN instance on a given Ethernet segment.
In this scenario, only one of the PEs, referred to as the Designated
Forwarder (DF), is responsible for certain actions:
* Sending broadcast and multicast traffic for a given EVI to that
CE.
* If the flooding of unknown unicast traffic (i.e., traffic for
which a PE does not know the destination MAC address, see
Section 12) is allowed, sending unknown unicast traffic for a
given EVI to that CE.
* If the multihoming mode is Single-Active, sending (known) unicast
traffic for a given EVI to that CE.
Note that this behavior, which allows selecting a DF at the
granularity of <ES, EVI> for is the default behavior in this
specification.
In this same scenario, a second PE referred to as the
Backup-Designated Forwarder (Backup-DF or BDF), is responsible for
assuming the role of DF in the event of DF's failure. Until this
occurs, the Backup-DF PE is a subset of, and behaves like, a Non-DF
PE for all forwarding considerations.
All other PEs, referred to as Non-Designated Forwarder (Non-DF or
NDF) are not responsible for any forwarding nor of assuming any
functionality from the DF in the event of its failure.
The default procedure for DF election at the granularity of <ES, EVI>
is referred to as "service carving". With service carving, it is
possible to perform load-balancing of traffic destined to a given
segment. The load-balancing procedure carves the set of EVIs on that
ES among the PEs nodes evenly such that every PE is the DF for a
disjoint and distinct set of EVIs for that ES. The procedure for
service carving is as follows according to the DF Election Finite
State Machine as defined in Section 2.1 of [RFC8584]:
1. When a PE discovers the ESI of the attached Ethernet segment, it
advertises an Ethernet Segment route with the associated
ES-Import extended community.
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2. The PE then starts a timer (default value = 3 seconds) to allow
the reception of Ethernet Segment routes from other PE nodes
connected to the same Ethernet segment. This timer value should
be the same across all PEs connected to the same Ethernet
segment.
3. When the timer expires, each PE builds an ordered list of the IP
addresses of all the PE nodes connected to the Ethernet segment
(including itself), in increasing numeric value. Each IP address
in this list is extracted from the "IP Address length" and
"Originating Router's IP address" fields of the advertised
Ethernet Segment route. Every PE is then given an ordinal
indicating its position in the ordered list, starting with 0 as
the ordinal for the PE with the lowest IP address length and
numeric value tuple. The tuple list is ordered by the IP address
length first and IP address value second. The ordinals are used
to determine which PE node will be the DF for a given EVPN
instance on the Ethernet segment, using the following rule:
Assuming a redundancy group of N PE nodes, the PE with ordinal i
is the DF for an <ES, EVI> when (V mod N) = i, where V is the
Ethernet tag for that EVI. For VLAN-Aware Bundle service, then
the numerically lowest Ethernet tag in that EVI MUST be used in
the modulo function.
It should be noted that using the "Originating Router's IP
address" field in the Ethernet Segment route to get the PE IP
address needed for the ordered list allows for a CE to be
multihomed across different ASes if such a need ever arises.
4. For each EVPN instance, a second list of the IP addresses of all
the PE nodes connected to the Ethernet segment is built. The PE
which was determined as DF above is removed from that ordered
candidate list, forming a backup redundancy group of M PE nodes.
Every remaining PE is then given a second ordinal indicating its
position in the secondary ordered list according to the same
criteria as in step 3 above.
The second ordinals are used to determine which PE nodes will be
the BDF for a given EVPN instance on the Ethernet segment, using
the same modulo rule as above, (V mod M) = i.
5. The PE that is elected as a DF for a given <ES, EVI> will unblock
BUM traffic, or all traffic if in Single-Active mode, for that
EVI on the corresponding ES. Note that the DF PE unblocks BUM
traffic in the egress direction towards the segment. All Non-DF
PEs, including the Backup-DF PE, continue to drop
multi-destination traffic in the egress direction towards that
<ES, EVI>.
In the case of link or port failure, the affected PE withdraws
its Ethernet Segment route. This will re-trigger the service
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carving procedures on all the PEs in the redundancy group: the
expected new-DF will be BDF previously calculated in step 5. For
PE node failure, or upon PE commissioning or decommissioning, the
PEs re-trigger the service carving. In the case of Single-Active
multihoming, when a service moves from one PE in the redundancy
group to another PE as a result of re-carving, the PE, which ends
up being the elected DF for the service, SHOULD trigger a MAC
address flush notification towards the associated Ethernet
segment. This can be done, for example, using the IEEE 802.1ak
Multiple VLAN Registration Protocol (MVRP) 'new' declaration.
It is RECOMMENDED that all future DF Election algorithms specify an
algorithm to select one Designated Forwarder (DF) PE, one Backup-DF
PE and a residual number of Non-DF PE(s).
8.6. Signaling Primary and Backup DF Elected PEs
Once the Primary and Backup DF Elected PEs for a given <ES, EVI> are
determined, the multi-homed PEs for that ES will each advertise an
Ethernet A-D per EVI route for that EVI and each will include an
L2-Attr extended community with the P and B bits set to reflect the
advertising PE's role for that EVI.
It should be noted if L2-Attr extended community is included for All-
Active mode, then the P bit must be set for all PEs in the redundancy
group.
8.7. Interoperability with Single-Homing PEs
Let's refer to PEs that only support single-homed CE devices as
single-homing PEs. For single-homing PEs, all the above multihoming
procedures can be omitted; however, to allow for single-homing PEs to
fully interoperate with multihoming PEs, some of the multihoming
procedures described above SHOULD be supported even by single- homing
PEs:
* procedures related to processing Ethernet A-D routes for the
purpose of fast convergence (Section 8.2 ("Fast Convergence")), to
let single-homing PEs benefit from fast convergence
* procedures related to processing Ethernet A-D routes for the
purpose of aliasing (Section 8.4 ("Aliasing and Backup Path")), to
let single-homing PEs benefit from load balancing
* procedures related to processing Ethernet A-D routes for the
purpose of a backup path (Section 8.4 ("Aliasing and Backup
Path")), to let single-homing PEs benefit from the corresponding
convergence improvement
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9. Determining Reachability to Unicast MAC Addresses
PEs forward packets that they receive based on the destination MAC
address. This implies that PEs must be able to learn how to reach a
given destination unicast MAC address.
There are two components to MAC address learning i.e. "local
learning" and "remote learning":
9.1. Local Learning
A particular PE must be able to learn the MAC addresses from the CEs
that are connected to it. This is referred to as local learning.
The PEs in a particular EVPN instance MUST support local data-plane
learning using standard IEEE Ethernet learning procedures. A PE must
be capable of learning MAC addresses in the data plane when it
receives packets from the CE network, including from:
* DHCP requests
* An ARP Request for its own MAC
* An ARP Request for a peer
Alternatively, PEs MAY learn the MAC addresses of the CEs in the
control plane or via management-plane integration between the PEs and
the CEs.
There are applications where a MAC address that is reachable via a
given PE on a locally attached segment (e.g., with ESI X) may move,
such that it becomes reachable via another PE on another segment
(e.g., with ESI Y). This is referred to as "MAC Mobility".
Procedures to support this are described in Section 15 ("MAC
Mobility").
9.2. Remote Learning
A particular PE must be able to determine how to send traffic to MAC
addresses that belong to or are behind CEs connected to other PEs,
i.e., to remote CEs or hosts behind remote CEs. Such MAC addresses
are referred to as "remote" MAC addresses.
This document requires a PE to learn remote MAC addresses in the
control plane. In order to achieve this, each PE advertises the MAC
addresses it learns from its locally attached CEs over the control
plane to all the other PEs in that EVPN instance, using MP-BGP and,
specifically, the MAC/IP Advertisement route.
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9.2.1. Constructing MAC/IP Address Advertisement
BGP is extended to advertise these MAC addresses using the MAC/IP
Advertisement route type in the EVPN NLRI.
The RD MUST be set per Section 7.9.
The Ethernet Segment Identifier is set to the 10-octet ESI described
in Section 5 ("Ethernet Segment").
The Ethernet Tag ID is set as defined in Section 6.
The MAC Address Length field is in bits, and it is set to 48. MAC
address length values other than 48 bits are outside the scope of
this document. The encoding of a MAC address MUST be the 6-octet MAC
address specified by [IEEE.802.1Q_2014] and [IEEE.802.1D_2004].
The IP Address field is optional. By default, the IP Address Length
field is set to 0, and the IP Address field is omitted from the
route. When a valid IP address needs to be advertised, it is then
encoded in this route. When an IP address is present, the IP Address
Length field is in bits, and it is set to 32 or 128 bits. Other IP
Address Length values are outside the scope of this document. The
encoding of an IP address MUST be either 4 octets for IPv4 or
16 octets for IPv6. The Length field of the EVPN NLRI (which is in
octets and is described in Section 7) is sufficient to determine
whether an IP address is encoded in this route and, if so, whether
the encoded IP address is IPv4 or IPv6.
The MPLS Label1 field is encoded as 3 octets, where the high-order
20 bits contain the label value. The MPLS Label1 MUST be downstream
assigned, and it is associated with the MAC address being advertised
by the advertising PE. The advertising PE uses this label when it
receives an MPLS-encapsulated packet to perform forwarding based on
the destination MAC address toward the CE. The forwarding procedures
are specified in Sections 13 and 14.
The choice of a particular label assignment methodology is purely
local to the PE that originates the route :
* A PE may advertise the same single EVPN label for all MAC
addresses in a given MAC-VRF. This label assignment is referred
to as a per MAC-VRF label assignment.
* Alternatively, a PE may advertise a unique EVPN label per <MAC-
VRF, Ethernet tag> combination. This label assignment is referred
to as a per <MAC-VRF, Ethernet tag> label assignment.
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* As a third option, a PE may advertise a unique EVPN label per
<ESI, Ethernet tag> combination. This label assignment is
referred to as a per <ESI, Ethernet tag> label assignment.
* As a fourth option, a PE may advertise a unique EVPN label per MAC
address. This label assignment is referred to as a per MAC label
assignment.
All of these label assignment methods have their trade-offs. An
assignment per MAC-VRF label requires the least number of EVPN labels
but requires a MAC lookup in addition to an MPLS lookup on an egress
PE for forwarding. On the other hand, a unique label per <ESI,
Ethernet tag> or a unique label per MAC allows an egress PE to
forward a packet that it receives from another PE, to the connected
CE, after looking up only the MPLS labels without having to perform a
MAC lookup. This includes the capability to perform appropriate VLAN
ID translation on egress to the CE.
The MPLS Label2 field is an optional field. If it is present, then
it is encoded as 3 octets, where the high-order 20 bits contain the
label value. Usage of the MPLS Label2 field is as per [RFC9135].
For cases which are not covered by the Symmetric IRB use-cases of
[RFC9135], Label2 SHOULD be set to zero by senders and SHOULD be
ignored by the receivers).
The Next Hop field of the MP_REACH_NLRI attribute of the route MUST
be set to the IPv4 or IPv6 address of the advertising PE.
The BGP advertisement for the MAC/IP Advertisement route MUST also
carry one or more Route Target (RT) extended communities. RTs may be
configured (as in IP VPNs) or may be derived automatically in the
"Unique VLAN EVPN" case from the Ethernet Tag (VLAN ID), as described
in Section 7.10.1.
It is to be noted that this document does not require PEs to create
forwarding state for remote MACs when they are learned in the control
plane. When this forwarding state is actually created is a local
implementation matter.
9.2.2. Route Resolution
If the Ethernet Segment Identifier field in a received MAC/IP
Advertisement route is set to the reserved ESI value of 0 or MAX-ESI,
then if the receiving PE decides to install forwarding state for the
associated MAC address, it MUST be based on the MAC/IP Advertisement
route alone.
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If the Ethernet Segment Identifier field in a received MAC/IP
Advertisement route is set to a non-reserved ESI, and the receiving
PE is locally attached to the same ESI, then the PE does not alter
its forwarding state based on the received route. This ensures that
local routes are preferred to remote routes.
If the Ethernet Segment Identifier field in a received MAC/IP
Advertisement route is set to a non-reserved ESI, then if the
receiving PE decides to install forwarding state for the associated
MAC address, it MUST be when both the MAC/IP Advertisement route AND
the associated set of Ethernet A-D per ES routes have been received.
The dependency of MAC route installation on Ethernet A-D per ES
routes is to ensure that MAC routes don't get accidentally installed
during a mass withdraw period.
To illustrate this with an example, consider two PEs (PE1 and PE2)
connected to a multihomed Ethernet segment ES1. All-Active
redundancy mode is assumed. A given MAC address M1 is learned by PE1
but not PE2. On PE3, the following states may arise:
T1 When the MAC/IP Advertisement route from PE1 and the set of
Ethernet A-D per ES routes and Ethernet A-D per EVI routes from
PE1 and PE2 are received, PE3 can forward traffic destined to
M1 to both PE1 and PE2.
T2 If after T1 PE1 withdraws its set of Ethernet A-D per ES
routes, then PE3 forwards traffic destined to M1 to PE2 only.
T2' If after T1 PE2 withdraws its set of Ethernet A-D per ES
routes, then PE3 forwards traffic destined to M1 to PE1 only.
T2'' If after T1 PE1 withdraws its MAC/IP Advertisement route, then
PE3 treats traffic to M1 as unknown unicast.
T3 PE2 also advertises a MAC route for M1, and then PE1 withdraws
its MAC route for M1. PE3 continues forwarding traffic
destined to M1 to both PE1 and PE2. In other words, despite M1
withdrawal by PE1, PE3 forwards the traffic destined to M1 to
both PE1 and PE2. This is because a flow from the CE,
resulting in M1 traffic getting hashed to PE1, can get
terminated, resulting in M1 being aged out in PE1; however, M1
can be reachable by both PE1 and PE2.
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10. ARP and ND
The IP Address field in the MAC/IP Advertisement route may optionally
carry one of the IP addresses associated with the MAC address. This
provides an option that can be used to minimize the flooding of ARP
or Neighbor Discovery (ND) messages over the MPLS network and to
remote CEs. This option also minimizes ARP (or ND) message
processing on end-stations/hosts connected to the EVPN network. A PE
may learn the IP address associated with a MAC address in the control
or management plane between the CE and the PE. Or, it may learn this
binding by snooping certain messages to or from a CE. When a PE
learns the IP address associated with a MAC address of a locally
connected CE, it may advertise this address to other PEs by including
it in the MAC/IP Advertisement route. The IP address may be an IPv4
address encoded using 4 octets or an IPv6 address encoded using
16 octets. For ARP and ND purposes, the IP Address Length field MUST
be set to 32 for an IPv4 address or 128 for an IPv6 address.
If there are multiple IP addresses associated with a MAC address,
then multiple MAC/IP Advertisement routes MUST be generated, one for
each IP address. For instance, this may be the case when there are
both an IPv4 and an IPv6 address associated with the same MAC address
for dual-IP-stack scenarios. When the IP address is dissociated with
the MAC address, then the MAC/IP Advertisement route with that
particular IP address MUST be withdrawn.
Note that a MAC-only route can be advertised along with, but
independent from, a MAC/IP route for scenarios where the MAC learning
over an access network/node is done in the data plane and independent
from ARP snooping that generates a MAC/IP route. In such scenarios,
when the ARP entry times out and causes the MAC/IP to be withdrawn,
then the MAC information will not be lost. In scenarios where the
host MAC/IP is learned via the management or control plane, then the
sender PE may only generate and advertise the MAC/IP route. If the
receiving PE receives both the MAC-only route and the MAC/IP route,
then when it receives a withdraw message for the MAC/IP route, it
MUST delete the corresponding entry from the ARP table but not the
MAC entry from the MAC-VRF table, unless it receives a withdraw
message for the MAC-only route.
When a PE receives an ARP Request for an IP address from a CE, and if
the PE has the MAC address binding for that IP address, the PE SHOULD
perform ARP proxy by responding to the ARP Request.
In the same way, when a PE receives a Neighbor Solicitation for an IP
address from a CE, the PE SHOULD perform ND proxy and respond if the
PE has the binding information for the IP.
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10.1. Default Gateway
When a PE needs to perform inter-subnet forwarding where each subnet
is represented by a different broadcast domain (e.g., a different
VLAN), the inter-subnet forwarding is performed at Layer 3, and the
PE that performs such a function is called the default gateway for
the EVPN instance. In this case, when the PE receives an ARP Request
for the IP address configured as the default gateway address, the PE
originates an ARP Reply.
Each PE that acts as a default gateway for a given EVPN instance MAY
advertise in the EVPN control plane its default gateway MAC address
using the MAC/IP Advertisement route, and each such PE indicates that
such a route is associated with the default gateway. This is
accomplished by requiring the route to carry the Default Gateway
extended community defined in Section 7.8 ("Default Gateway Extended
Community"). The ESI field is set to zero when advertising the MAC
route with the Default Gateway extended community.
The IP Address field of the MAC/IP Advertisement route is set to the
default gateway IP address for that subnet (e.g., an EVPN instance).
For a given subnet (e.g., a VLAN or EVPN instance), the default
gateway IP address is the same across all the participant PEs. The
inclusion of this IP address enables the receiving PE to check its
configured default gateway IP address against the one received in the
MAC/IP Advertisement route for that subnet (or EVPN instance), and if
there is a discrepancy, then the PE SHOULD notify the operator and
log an error message.
Unless it is known a priori (by means outside of this document) that
all PEs of a given EVPN instance act as a default gateway for that
EVPN instance, the MPLS label MUST be set to a valid downstream
assigned label.
Furthermore, even if all PEs of a given EVPN instance do act as a
default gateway for that EVPN instance, but only some, but not all,
of these PEs have sufficient (routing) information to provide
inter-subnet routing for all the inter-subnet traffic originated
within the subnet associated with the EVPN instance, then when such a
PE advertises in the EVPN control plane its default gateway MAC
address using the MAC/IP Advertisement route and indicates that such
a route is associated with the default gateway, the route MUST carry
a valid downstream assigned label.
Each PE that receives this route and imports it as per procedures
specified in this document follows the procedures in this section
when replying to ARP Requests that it receives.
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Each PE that acts as a default gateway for a given EVPN instance that
receives this route and imports it as per procedures specified in
this document MUST create MAC forwarding state that enables it to
apply IP forwarding to the packets destined to the MAC address
carried in the route.
10.1.1. Best Path Selection for Default Gateway
Default gateway MAC address that is assigned to an Integrated Routing
and Bridging (IRB) interface (for a subnet) in a PE MUST be unique in
context of that subnet. In other words, the same MAC address cannot
be used by a host either intentionally or accidentally. In order to
properly detect such conflicts, the BGP best path selection rules in
Section 7.13.1 MUST be applied, and in case such conflicts arises :
* The PE that has advertised the MAC route without Default Gateway
extended community, upon receiving the route with Default Gateway
extended community, SHALL withdraw its route and SHOULD raise an
alarm.
* MAC Mobility extended community SHALL NOT be attached to routes
which also have Default Gateway extended community on the sending
side and SHALL be ignored on the receiving side.
11. Handling of Multi-destination Traffic
Procedures are required for a given PE to flood broadcast or
multicast traffic received from a CE and with a given Ethernet tag to
the other PEs in the associated <EVI, BD> (EVPN instance). In
certain scenarios, as described in Section 12 ("Processing of Unknown
Unicast Packets"), a given PE may also need to flood unknown unicast
traffic to other PEs.
The PEs in a particular EVPN instance may use ingress replication,
P2MP LSPs, or MP2MP LSPs to send unknown unicast, broadcast, or
multicast traffic to other PEs.
Each PE MUST advertise an "Inclusive Multicast Ethernet Tag route" to
enable the above. The following subsection provides the procedures
to construct the Inclusive Multicast Ethernet Tag route. Subsequent
subsections describe its usage in further detail.
11.1. Constructing Inclusive Multicast Ethernet Tag Route
The RD MUST be set per Section 7.9.
The Ethernet Tag ID is set as defined in Section 6.
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The Originating Router's IP Address field value MUST be set to an IP
address of the PE that should be common for all the EVIs on the PE
(e.g., this address may be the PE's loopback address). The IP
Address Length field is in bits.
The Next Hop field of the MP_REACH_NLRI attribute of the route MUST
be set to the IPv4 or IPv6 address of the advertising PE.
The BGP advertisement for the Inclusive Multicast Ethernet Tag route
MUST also carry one or more Route Target (RT) extended communities.
The assignment of RTs as described in Section 7.10 MUST be followed.
11.2. P-Tunnel Identification
In order to identify the P-tunnel used for sending broadcast, unknown
unicast, or multicast traffic, the Inclusive Multicast Ethernet Tag
route MUST carry a Provider Multicast Service Interface (PMSI) Tunnel
attribute as specified in [RFC6514].
Depending on the technology used for the P-tunnel for the EVPN
instance on the PE, the PMSI Tunnel attribute of the Inclusive
Multicast Ethernet Tag route is constructed as follows.
* If the PE that originates the advertisement uses a P-multicast
tree for the P-tunnel for EVPN, the PMSI Tunnel attribute MUST
contain the identity of the tree (note that the PE could create
the identity of the tree prior to the actual instantiation of the
tree).
* A PE that uses a P-multicast tree for the P-tunnel MAY aggregate
two or more Broadcast Domains (BDs) present on the PE onto the
same tree. In this case, in addition to carrying the identity of
the tree, the PMSI Tunnel attribute MUST carry an MPLS label,
which the PE has bound uniquely to the BD associated with this
update (as determined by its RTs and Ethernet Tag ID). The
assigned MPLS label is upstream allocated unless the procedures in
section 19 (Use of Domain-wide Common Block (DCB) Labels) are
followed. If the PE has already advertised Inclusive Multicast
Ethernet Tag routes for two or more BDs that it now desires to
aggregate, then the PE MUST re-advertise those routes. The
re-advertised routes MUST be the same as the original ones, except
for the PMSI Tunnel attribute and the label carried in that
attribute.
* If the PE that originates the advertisement uses ingress
replication for the P-tunnel for EVPN, the route MUST include the
PMSI Tunnel attribute with the Tunnel Type set to Ingress
Replication and the Tunnel Identifier set to a routable address of
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the PE. The PMSI Tunnel attribute MUST carry a downstream
assigned MPLS label. This label is used to demultiplex the
broadcast, multicast, or unknown unicast EVPN traffic received
over an MP2P tunnel by the PE. A PE receiving an Inclusive
Multicast Ethernet Tag route (with ingress replication as
P-tunnel) SHOULD use the Next Hop field of the MP_REACH_NLRI
attribute when resolving the route to an LSP.
12. Processing of Unknown Unicast Packets
The procedures in this document do not require the PEs to flood
unknown unicast traffic to other PEs. If PEs learn CE MAC addresses
via a control-plane protocol, the PEs can then distribute MAC
addresses via BGP, and all unicast MAC addresses will be learned
prior to traffic to those destinations.
However, if a destination MAC address of a received packet is not
known by the PE, the PE may have to flood the packet. When flooding,
one must take into account "split-horizon forwarding" as follows: The
principles behind the following procedures are borrowed from the
split-horizon forwarding rules in VPLS solutions [RFC4761] [RFC4762].
When a PE capable of flooding (say PEx) receives an unknown
destination MAC address, it floods the frame. If the frame arrived
from an attached CE, PEx must send a copy of that frame on every
Ethernet segment (belonging to that EVI) for which it is the DF,
other than the Ethernet segment on which it received the frame. In
addition, the PE must flood the frame to all other PEs participating
in that EVPN instance. If, on the other hand, the frame arrived from
another PE (say PEy), PEx must send a copy of the packet on each
Ethernet segment (belonging to that EVI) for which it is the DF. PEx
MUST NOT send the frame to other PEs, since PEy would have already
done so. Split-horizon forwarding rules apply to unknown MAC
addresses.
Whether or not to flood packets to unknown destination MAC addresses
should be an administrative choice, depending on how learning happens
between CEs and PEs.
The PEs in a particular EVPN instance may use ingress replication
using RSVP-TE P2P LSPs or LDP MP2P LSPs for sending unknown unicast
traffic to other PEs. Or, they may use RSVP-TE P2MP or LDP P2MP for
sending such traffic to other PEs.
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12.1. Ingress Replication
If ingress replication is in use, the P-tunnel attribute, carried in
the Inclusive Multicast Ethernet Tag routes for the EVPN instance,
specifies the downstream label that the other PEs can use to send
unknown unicast, multicast, or broadcast traffic for that EVPN
instance to this particular PE.
The PE that receives a packet with this particular MPLS label MUST
treat the packet as a broadcast, multicast, or unknown unicast
packet. Further, if the MAC address is a unicast MAC address, the PE
MUST treat the packet as an unknown unicast packet.
12.2. P2MP MPLS LSPs
The procedures for using P2MP or MP2MP LSPs are very similar to the
VPLS procedures described in [RFC7117]. The P-tunnel attribute used
by a PE for sending unknown unicast, broadcast, or multicast traffic
for a particular EVPN instance is advertised in the Inclusive
Multicast Ethernet Tag route as described in Section 11 ("Handling of
Multi-destination Traffic").
The P-tunnel attribute specifies the P2MP or MP2MP LSP identifier.
This is the equivalent of an Inclusive tree as described in
[RFC7117]. Note that multiple BDs in the same or different EVIs may
use the same P2MP or MP2MP LSP, using upstream labels [RFC7117] or
DCB labels [I-D.ietf-bess-mvpn-evpn-aggregation-label]. This is the
equivalent of an Aggregate Inclusive tree [RFC7117]. When P2MP or
MP2MP LSPs are used for flooding unknown unicast traffic, packet
reordering is possible.
The PE that receives a packet on the P2MP or MP2MP LSP specified in
the PMSI Tunnel attribute MUST treat the packet as a broadcast,
multicast, or unknown unicast packet. Further, if the MAC address is
a unicast MAC address, the PE MUST treat the packet as an unknown
unicast packet.
13. Forwarding Unicast Packets
This section describes procedures for forwarding unicast packets by
PEs, where such packets are received from either directly connected
CEs or some other PEs.
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13.1. Forwarding Packets Received from a CE
When a PE receives a packet from a CE with a given Ethernet Tag, it
must first look up the packet's source MAC address. In certain
environments that enable MAC security, the source MAC address MAY be
used to validate the host identity and determine that traffic from
the host can be allowed into the network. Source MAC lookup MAY also
be used for local MAC address learning.
If the PE decides to forward the packet, the destination MAC address
of the packet must be looked up. If the PE has received MAC address
advertisements for this destination MAC address from one or more
other PEs or has learned it from locally connected CEs, the MAC
address is considered a known MAC address. Otherwise, it is
considered an unknown MAC address.
For known MAC addresses, the PE forwards this packet to one of the
remote PEs or to a locally attached CE. When forwarding to a remote
PE, the packet is encapsulated in the EVPN MPLS label advertised by
the remote PE, for that MAC address, and in the MPLS LSP label stack
to reach the remote PE.
If the MAC address is unknown and if the administrative policy on the
PE requires flooding of unknown unicast traffic, then:
* The PE MUST flood the packet to other PEs. The PE MUST first
encapsulate the packet in the ESI MPLS label as described in
Section 8.3.
If ingress replication is used, the packet MUST be replicated to
each remote PE, with the VPN label being the MPLS label advertised
by the remote PE in a PMSI Tunnel attribute in the Inclusive
Multicast Ethernet Tag route for the <EVI, BD> associated with the
received packet's Ethernet tag.
If P2MP LSPs are being used, the packet MUST be sent on the P2MP
LSP of which the PE is the root, for the <EVI, BD> associated with
the received packet's Ethernet tag. If the same P2MP LSP is used
for all the BD's in the EVI, then all the PEs in the EVI MUST be
the leaves of the P2MP LSP. If a different P2MP LSP is used for a
given BD in the EVI, then only the PEs in that BD MUST be the
leaves of the P2MP LSP. The packet MUST be encapsulated in the
P2MP LSP label stack.
If the MAC address is unknown, then, if the administrative policy on
the PE does not allow flooding of unknown unicast traffic:
* The PE MUST drop the packet.
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13.2. Forwarding Packets Received from a Remote PE
This section describes the procedures for forwarding known and
unknown unicast packets received from a remote PE.
13.2.1. Unknown Unicast Forwarding
When a PE receives an MPLS packet from a remote PE, then, after
processing the MPLS label stack, if the top MPLS label ends up being
a P2MP LSP label associated with an EVPN instance or -- in the case
of ingress replication -- the downstream label advertised in the
P-tunnel attribute, and after performing the split-horizon procedures
described in Section 8.3:
* If the PE is the designated forwarder of BUM traffic on a
particular set of ESes for the <EVI, BD>, the default behavior is
for the PE to flood that traffic to these ESes. In other words,
the default behavior is for the PE to assume that for BUM traffic
it is not required to perform a destination MAC address lookup.
As an option, the PE may perform a destination MAC lookup to flood
the packet to only a subset of these ESes. For instance, the PE
may decide to not flood a BUM packet on certain Ethernet segments
even if it is the DF on the Ethernet segment, based on
administrative policy.
* If the PE is not the designated forwarder for any ES associated
with the <EVI, BD>, the default behavior is for it to drop the BUM
traffic.
13.2.2. Known Unicast Forwarding
If the top MPLS label ends up being an EVPN label that was advertised
in the unicast MAC advertisements, then the PE either forwards the
packet based on CE next-hop forwarding information associated with
the label or does a destination MAC address lookup to forward the
packet to a CE.
14. Load Balancing of Unicast Packets
This section specifies the load-balancing procedures for sending
known unicast packets to a multihomed CE.
14.1. Load Balancing of Traffic from a PE to Remote CEs
When a remote PE imports a MAC/IP Advertisement route for a given ES
in a MAC-VRF, it MUST examine all imported Ethernet A-D routes for
that ESI in order to determine the load- balancing characteristics of
the Ethernet segment.
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14.1.1. Single-Active Redundancy Mode
For a given ES, if a remote PE has imported the set of Ethernet A-D
per ES routes from at least one PE, where the "Single-Active" flag in
the ESI Label extended community is set, then that remote PE MUST
deduce that the ES is operating in Single-Active redundancy mode.
This means that for a given <EVI, BD>, a given MAC address is only
reachable only via the PE announcing the associated MAC/IP
Advertisement route - this PE will also have advertised an Ethernet
A-D per EVI route for that <EVI, BD> with an L2-Attr extended
community in which the P bit is set. I.e., the Primary DF Elected PE
is also responsible for sending known unicast frames to the CE and
receiving unicast and BUM frames from it. Similarly, the Backup DF
Elected PE will have advertised an Ethernet AD per EVI route for
<EVI, BD> with an L2-Attr extended community in which the B bit is
set.
If the Primary DF Elected PE loses connectivity to the CE it SHOULD
withdraw its set of Ethernet A-D per ES routes for the affected ES
prior to withdrawing the affected MAC/IP Advertisement routes. The
Backup DF Elected PE (which is now the Primary DF Elected PE) needs
to advertise an Ethernet A-D per EVI route for <EVI, BD> with an
L2-Attr extended community in which the P bit is set. Furthermore,
the new Backup DF Elected PE needs to advertise an Ethernet A-D per
EVI route for <EVI, BD> with an L2-Attr extended community in which
the B bit is set.
A remote PE SHOULD use the Primary DF Elected PE's withdrawal of its
set of Ethernet A-D per ES routes as a trigger to update its
forwarding entries for the associated MAC addresses to point at the
Backup DF Elected PE. As the Backup DF Elected PE starts learning
the MAC addresses over its attached ES, it will start sending MAC/IP
Advertisement routes while the failed PE withdraws its routes. This
mechanism minimizes the flooding of traffic during fail-over events.
14.1.2. All-Active Redundancy Mode
For a given ES, if the remote PE has imported the set of Ethernet A-D
per ES routes from one or more PEs and none of them have the
"Single-Active" flag in the ESI Label extended community set, then
the remote PE MUST deduce that the ES is operating in All-Active
redundancy mode. A remote PE that receives a MAC/IP Advertisement
route with a non-reserved ESI SHOULD consider the advertised MAC
address to be reachable via all PEs that have advertised reachability
to that MAC address's EVI/ES/Ethernet Tag ID via the combination of
an Ethernet A-D per EVI route for that EVI/ES/Ethernet Tag ID AND an
Ethernet A-D per ES route for that ES. The remote PE MUST use
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received MAC/IP Advertisement routes and Ethernet A-D per EVI/per ES
routes to construct the set of next hops for the advertised MAC
address.
Each next hop comprises an MPLS label stack that is to be used to
reach a given egress PE and allow it to forward a packet. The
portion of the MPLS label stack that is to be used by that egress PE
to forward a packet is constructed by the remote PE as follows:
* If a MAC/IP Advertisement route was received from that PE, then
its label stack MUST be used in the next hop.
* Otherwise, the label stack from the Ethernet A-D per EVI route
that matches the MAC address' EVI/ES/Ethernet Tag ID MUST be used
in the next hop.
The following example explains the above.
Consider a CE (CE1) that is dual-homed to two PEs (PE1 and PE2) on a
LAG interface (ES1), and is sending packets with source MAC address
MAC1 on VLAN1 (mapped to EVI1). A remote PE, say PE3, is able to
learn that MAC1 is reachable via PE1 and PE2. Both PE1 and PE2 may
advertise MAC1 if they receive packets with MAC1 from CE1. If this
is not the case, and if MAC1 is advertised only by PE1, PE3 still
considers MAC1 as reachable via both PE1 and PE2, as both PE1 and PE2
advertise a set of Ethernet A-D per ES routes for ES1 as well as an
Ethernet A-D per EVI route for <EVI1, ES1>.
The MPLS label stack to send the packets to PE1 is the MPLS LSP stack
to get to PE1 (at the top of the stack) followed by the EVPN label
advertised by PE1 for CE1's MAC.
The MPLS label stack to send packets to PE2 is the MPLS LSP stack to
get to PE2 (at the top of the stack) followed by the MPLS label in
the Ethernet A-D route advertised by PE2 for <EVI1, ES1>, if PE2 has
not advertised MAC1 in BGP.
We will refer to these label stacks as MPLS next hops.
The remote PE (PE3) can now load balance the traffic it receives from
its CEs, destined for CE1, between PE1 and PE2. PE3 may use N-tuple
flow information to hash traffic into one of the MPLS next hops for
load balancing of IP traffic. Alternatively, PE3 may rely on the
source MAC addresses for load balancing.
Note that once PE3 decides to send a particular packet to PE1 or PE2,
it can pick one out of multiple possible paths to reach the
particular remote PE using regular MPLS procedures. For instance, if
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the tunneling technology is based on RSVP-TE LSPs and PE3 decides to
send a particular packet to PE1, then PE3 can choose from multiple
RSVP-TE LSPs that have PE1 as their destination.
When PE1 or PE2 receives the packet destined for CE1 from PE3, if the
packet is a known unicast, it is forwarded to CE1.
14.2. Load Balancing of Traffic between a PE and a Local CE
A CE may be configured with more than one interface connected to
different PEs or the same PE for load balancing, using a technology
such as a LAG. The PE(s) and the CE can load balance traffic onto
these interfaces using one of the following mechanisms.
14.2.1. Data-Plane Learning
Consider that the PEs perform data-plane learning for local MAC
addresses learned from local CEs. This enables the PE(s) to learn a
particular MAC address and associate it with one or more interfaces,
if the technology between the PE and the CE supports multipathing.
The PEs can now load balance traffic destined to that MAC address on
the multiple interfaces.
Whether the CE can load balance traffic that it generates on the
multiple interfaces is dependent on the CE implementation.
14.2.2. Control-Plane Learning
The CE can be a host that advertises the same MAC address using a
control protocol on all interfaces. This enables the PE(s) to learn
the host's MAC address and associate it with all interfaces. The PEs
can now load balance traffic destined to the host on all these
interfaces. The host can also load balance the traffic it generates
onto these interfaces, and the PE that receives the traffic employs
EVPN forwarding procedures to forward the traffic.
15. MAC Mobility
It is possible for a given host or end-station (as defined by its MAC
address) to move from one Ethernet segment to another; this is
referred to as 'MAC Mobility' or 'MAC move', and it is different from
the multihoming situation in which a given MAC address is reachable
via multiple PEs for the same Ethernet segment. In a MAC move, there
would be two sets of MAC/IP Advertisement routes -- one set with the
new Ethernet segment and one set with the previous Ethernet segment
-- and the MAC address would appear to be reachable via each of these
segments.
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In order to allow all of the PEs in the EVPN instance to correctly
determine the current location of the MAC address, all advertisements
of it being reachable via the previous Ethernet segment MUST be
withdrawn by the PEs, for the previous Ethernet segment, that had
advertised it.
If local learning is performed using the data plane, these PEs will
not be able to detect that the MAC address has moved to another
Ethernet segment, and the receipt of MAC/IP Advertisement routes,
with the MAC Mobility extended community, from other PEs serves as
the trigger for these PEs to withdraw their advertisements. If local
learning is performed using the control or management planes, these
interactions serve as the trigger for these PEs to withdraw their
advertisements.
In a situation where there are multiple moves of a given MAC,
possibly between the same two Ethernet segments, there may be
multiple withdrawals and re-advertisements. In order to ensure that
all PEs in the EVPN instance receive all of these correctly through
the intervening BGP infrastructure, introducing a sequence number
into the MAC Mobility extended community is necessary.
In order to process mobility events correctly, an implementation MUST
handle scenarios in which sequence number wraparound occurs.
Every MAC mobility event for a given MAC address will contain a
sequence number that is set using the following rules:
* A PE advertising a MAC address for the first time advertises it
with no MAC Mobility extended community.
* A PE detecting a locally attached MAC address for which it had
previously received a MAC/IP Advertisement route with a different
Ethernet segment identifier advertises the MAC address in a MAC/IP
Advertisement route tagged with a MAC Mobility extended community
with a sequence number one greater than the sequence number in the
MAC Mobility extended community of the received MAC/IP
Advertisement route. In the case of the first mobility event for
a given MAC address, where the received MAC/IP Advertisement route
does not carry a MAC Mobility extended community, the value of the
sequence number in the received route is assumed to be 0 for the
purpose of this processing.
* A PE detecting a locally attached MAC address for which it had
previously received a MAC/IP Advertisement route with the same
non-zero Ethernet segment identifier advertises it with:
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1. no MAC Mobility extended community, if the received route did
not carry said extended community.
2. a MAC Mobility extended community with the sequence number
equal to the highest of the sequence number(s) in the received
MAC/IP Advertisement route(s), if the received route(s) is
(are) tagged with a MAC Mobility extended community.
* A PE detecting a locally attached MAC address for which it had
previously received a MAC/IP Advertisement route with the same
zero Ethernet segment identifier (single-homed scenarios)
advertises it with a MAC Mobility extended community with the
sequence number set properly. In the case of single-homed
scenarios, there is no need for ESI comparison. ESI comparison is
done for multihoming in order to prevent false detection of MAC
moves among the PEs attached to the same multihomed site.
A PE receiving a MAC/IP Advertisement route for a MAC address with a
different Ethernet segment identifier and a higher sequence number
than that which it had previously advertised withdraws its MAC/IP
Advertisement route. If two (or more) PEs advertise the same MAC
address with the same sequence number but different Ethernet segment
identifiers, a PE that receives these routes selects the route
advertised by the PE with the lowest IP address as the best route.
If the PE is the originator of the MAC route and it receives the same
MAC address with the same sequence number that it generated, it will
compare its own IP address with the IP address of the remote PE and
will select the lowest IP. If its own route is not the best one, it
will withdraw the route.
15.1. MAC Duplication Issue
A situation may arise where the same MAC address is learned by
different PEs in the same VLAN because of two (or more) hosts being
misconfigured with the same (duplicate) MAC address. In such a
situation, the traffic originating from these hosts would trigger
continuous MAC moves among the PEs attached to these hosts. It is
important to recognize such a situation and avoid incrementing the
sequence number (in the MAC Mobility extended community) to infinity.
In order to remedy such a situation, a PE that detects a MAC mobility
event via local learning starts an M-second timer (with a default
value of M = 180), and if it detects N MAC moves before the timer
expires (with a default value of N = 5), it concludes that a
duplicate-MAC situation has occurred. The PE MUST alert the operator
and stop sending, updating or processing any BGP MAC/IP Advertisement
routes for that MAC address until a corrective action is taken by the
operator. The values of M and N MUST be configurable to allow for
flexibility in operator control. Note that the other PEs in the EVPN
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instance will forward the traffic for the duplicate MAC address to
one of the PEs advertising the duplicate MAC address.
15.2. Sticky MAC Addresses
There are scenarios in which it is desired to configure some MAC
addresses as static so that they are not subjected to MAC moves. In
such scenarios, these MAC addresses are advertised with a MAC
Mobility extended community where the static flag is set to one and
the sequence number is set to zero. If a PE receives such
advertisements, then it MAY program to drop any received frames with
that MAC SA over its local ACs. When a PE later learns the same MAC
address(es) via local learning for remote PEs or via a different ES
for the advertising PE, then the PE MUST alert the operator and MAY
drop the received frames.
[RFC9135] describes symmetric and asymmetric IRB operation where an
access-facing IRB interface is associcated with each subnet (i.e.,
VLAN). Each of these IRB interfaces is configured with a MAC address
(typically Anycast) and an Anycast IP address. The MAC address
associated with an IRB interface should be considered as sticky MAC
address and be programmed as such for local ACs. If this MAC address
is not Anycast, then it is advertised with both Gateway Extended EC
and MAC Mobility EC with static flag set; however, if it is Anycast,
then no EVPN MAC/IP route advertisement is needed
[RFC9136] describes interfaceful IRB interfaces that each is
configured with a MAC address. This MAC address for each of these
core-facing IRB interfaces should be considered as a sticky MAC
address and be advertised with static flag of one and sequence number
of zero and be programmed as a sticky MAC.
15.3. Loop Protection
The EVPN MAC Duplication procedure in Section 15.1 prevents an
endless EVPN MAC/IP route advertisement exchange for a duplicate MAC
between two (or more) PEs. This helps the control plane settle,
however, when there is backdoor link (loop) between two or more PEs
attached to the same BD, BUM frames being sent by a CE are still
endlessly looped within the BD through the backdoor link and among
the PEs. This may cause unpredictable issues in the CEs connected to
the affected BD.
The EVPN MAC Duplication Mechanism in Section 15.1 MAY be extended
with a Loop-protection action that is applied on the duplicate-MAC
addresses. This additional mechanism resolves loops created by
accidental or intentional backdoor links and SHOULD be enabled in all
the PEs attached to the BD.
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After following the procedure in Section 15.1, when a PE detects a
MAC M as duplicate, the PE behaves as follows:
a) Stops advertising M and logs a duplicate event.
b) Initializes a retry-timer, R seconds.
c) Since Loop Protection is enabled, the PE executes a Loop
Protection action referred to as "Drop" M.
When the PE programs M as a "Drop" MAC, then it drops any received
frames with MAC-SA that is the same as "Drop" MAC (e.g., duplicate
MAC). The PE MAY keep a counter for such discarded frames for each
duplicate (dropped) MAC address or an aggregate counter for all
duplicate (dropped) MAC addresses. The PE MAY program M as a "Drop"
MAC on its local ACs if it receives from remote PE(s) a MAC/IP route
update for M with the sticky-bit set (in the MAC Mobility extended
community).
At this point and while M is in "Drop" state:
a) If a new frame is received (on its local AC) with MAC SA = M, the
PE identifies M to be discarded thus ending the loop.
b) Optionally, instead of simply discarding the frame with MAC SA =
M, the PE MAY bring down the AC on which the offending frame is
seen last.
c) Optionally, any frame that arrives at the PE with MAC DA = M
SHOULD be discarded too.
When the retry-timer R for M expires, the PE removes the "Drop"
filter on M and the MAC duplicate detection process is restarted. In
general, the "Drop" filter on a MAC M can be removed if any of the
following events occur:
* Retry-timer R for duplicate-MAC M expires (as discussed). R is
initialized when M is detected as duplicate-MAC. Its value is
configurable and SHOULD be at least three times the EVPN MAC
Duplication M-timer window.
* The operator manually removes the filter on MAC M. This should be
done only if the conditions under which M was identified as
duplicate have been cleared.
* The remote PE withdraws the MAC/IP route for M and there are no
other remote MAC/IP routes for M.
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16. Multicast and Broadcast
The PEs in a particular EVPN instance may use ingress replication or
P2MP or MP2MP LSPs to send multicast traffic to other PEs.
16.1. Ingress Replication
The PEs may use ingress replication for flooding BUM traffic as
described in Section 11 ("Handling of Multi-destination Traffic"). A
given broadcast packet must be sent to all the remote PEs. However,
a given multicast packet for a multicast flow may be sent to only a
subset of the PEs. Specifically, a given multicast flow may be sent
to only those PEs that have receivers that are interested in the
multicast flow. Determining which of the PEs have receivers for a
given multicast flow is done using the procedures of [RFC9251].
16.2. P2MP or MP2MP LSPs
A PE may use an "Inclusive" tree for sending a BUM packet. This
terminology is borrowed from [RFC7117].
A variety of transport technologies may be used in the service
provider (SP) network. For Inclusive P-multicast trees, these
transport technologies include point-to-multipoint LSPs created by
RSVP-TE or Multipoint LDP (mLDP) or BIER.
16.2.1. Inclusive Trees
An Inclusive tree allows the use of a single multicast distribution
tree, referred to as an Inclusive P-multicast tree, in the SP network
to carry all the multicast traffic from a specified set of EVPN
instances on a given PE. A particular P-multicast tree can be set up
to carry the traffic originated by sites belonging to a single EVPN
instance, or to carry the traffic originated by sites belonging to
several EVPN instances. The ability to carry the traffic of more
than one EVPN instance on the same tree is termed 'Aggregation', and
the tree is called an Aggregate Inclusive P-multicast tree or
Aggregate Inclusive tree for short. The Aggregate Inclusive tree
needs to include every PE that is a member of any of the EVPN
instances that are using the tree. This implies that a PE may
receive BUM traffic even if it doesn't have any receivers that are
interested in receiving that traffic.
An Inclusive or Aggregate Inclusive tree as defined in this document
is a P2MP tree. A P2MP or MP2MP tree is used to carry traffic only
for EVPN CEs that are connected to the PE that is the root of the
tree.
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The procedures for signaling an Inclusive tree are the same as those
in [RFC7117], with the VPLS A-D route replaced with the Inclusive
Multicast Ethernet Tag route. The P-tunnel attribute [RFC7117] for
an Inclusive tree is advertised with the Inclusive Multicast Ethernet
Tag route as described in Section 11 ("Handling of Multi-destination
Traffic"). Note that for an Aggregate Inclusive tree, a PE can
"aggregate" multiple EVPN instances on the same P2MP LSP using
upstream labels or DCB allocated labels
[I-D.ietf-bess-mvpn-evpn-aggregation-label]. The procedures for
aggregation are the same as those described in [RFC7117], with VPLS
A-D routes replaced by EVPN Inclusive Multicast Ethernet Tag routes.
17. Convergence
This section describes failure recovery from different types of
network failures.
17.1. Transit Link and Node Failures between PEs
The use of existing MPLS fast-reroute mechanisms can provide failure
recovery on the order of 50 ms, in the event of transit link and node
failures in the infrastructure that connects the PEs.
17.2. PE Failures
Consider a host CE1 that is dual-homed to PE1 and PE2. If PE1 fails,
a remote PE, PE3, can discover this based on the failure of the BGP
session. This failure detection can be in the sub-second range if
Bidirectional Forwarding Detection (BFD) is used to detect BGP
session failures. PE3 can update its forwarding state to start
sending all traffic for CE1 to only PE2.
17.3. PE-to-CE Network Failures
If the connectivity between the multihomed CE and one of the PEs to
which it is attached fails, the PE MUST withdraw the set of Ethernet
A-D per ES routes that had been previously advertised for that ES.
This enables the remote PEs to remove the MPLS next hop to this
particular PE from the set of MPLS next hops that can be used to
forward traffic to the CE. When the MAC entry on the PE ages out,
the PE MUST withdraw the MAC address from BGP.
When an EVI is decommissioned on an Ethernet segment the PE MUST
withdraw the Ethernet A-D per EVI route(s) announced for that <EVI,
ES>. In addition, the PE MUST also withdraw the MAC/IP Advertisement
routes that are impacted by the decommissioning.
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The Ethernet A-D per ES routes should be used by an implementation to
optimize the withdrawal of MAC/IP Advertisement routes. When a PE
receives a withdrawal of a particular Ethernet A-D route from an
advertising PE, it SHOULD consider all the MAC/IP Advertisement
routes that are learned from the same ESI as in the Ethernet A-D
route from the advertising PE as having been withdrawn. This
optimizes the network convergence times in the event of PE-to-CE
failures.
18. Frame Ordering
In a MAC address, if the value of the first nibble (bits 8 through 5)
of the most significant octet of the destination MAC address (which
follows the last MPLS label) happens to be 0x4 or 0x6, then the
Ethernet frame can be misinterpreted as an IPv4 or IPv6 packet by
intermediate P nodes performing ECMP based on deep packet inspection,
thus resulting in load balancing packets belonging to the same flow
on different ECMP paths and subjecting those packets to different
delays. Therefore, packets belonging to the same flow can arrive at
the destination out of order. This out-of-order delivery can happen
during steady state in the absence of any failures, resulting in
significant impact on network operations.
In order to avoid frame misordering described in the above paragraph,
the following network-wide rules are applied:
* If a network uses deep packet inspection for its ECMP, then the
the following rules for "Preferred PW MPLS Control Word" [RFC4385]
apply:
- It MUST be used with the value 0 (e.g., a 4-octet field with a
value of zero) when sending unicast EVPN-encapsulated packets
over an MP2P LSP.
- It SHOULD NOT be used when sending EVPN-encapsulated packets
over a P2MP or P2P RSVP-TE LSP.
- It SHOULD be used with the value 0 when sending EVPN-
encapsulated packets over a mLDP P2MP LSP. There can be
scenarios where multiple links or tunnels can exist between two
nodes and thus it is important to ensure that all packets for a
given flows take the same link (or tunnel) between the two
nodes.
* If a network (inclusive of all PE and P nodes) uses entropy labels
per [RFC6790] for ECMP load balancing, then the control word MAY
NOT be used.
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18.1. Flow Label
Flow label is used to add entropy to divisible flows, and creates
ECMP load-balancing in the network. The Flow label MAY be used in
EVPN networks to achieve better load-balancing in the network, when
transit nodes perform deep packet inspection for ECMP hashing. The
following rules apply:
* When F-bit is set to 1, the PE announces the capability of both
sending and receiving flow label for known unicast.
If the PE is capable itself of supporting Flow Label, then:
- upon receiving the F-bit set (F=1) from a remote PE, it MUST
send known unicast packets to that PE with Flow labels;
- alternately, upon receiving the F-bit unset (F=0) from a
remote PE, it MUST NOT send known unicast packets to that PE
with Flow labels.
When a PE that doesn't support flow label, receives the F-bit set
(F=1) from a remote PE, it takes the following actions: a) it
notifies the operator and b) it excludes the remote PE as the EVPN
destination for any of the corresponding service instances. See
Section 7.11.2
* The Flow Label MUST NOT be used for EVPN-encapsulated BUM packets.
* An ingress PE will push the Flow Label at the bottom of the stack
of the EVPN-encapsulated known unicast packets sent to an egress
PE that previously signaled F-bit set to 1.
* If a PE receives a unicast packet with two labels, then it can
differentiate between [VPN label + ESI label] and [VPN label +
Flow label] and there should be no ambiguity between ESI and Flow
labels even if they overlap. The reason for this is that the
downstream assigned VPN label for known unicast is different than
for BUM traffic and ESI label (if present) comes after BUM VPN
label. The receiving PE knows from th VPN label whether the next
label is an ESI label or a Flow label - i.e., if the VPN label is
for known unicast, then the next label MUST be a flow label and if
the VPN label is for BUM traffic, then the next label MUST be an
ESI label because BUM packets are not sent with Flow labels.
* When sending EVPN-encapsulated packets over a P2MP LSP (either
RSVP-TE or mLDP), flow label SHOULD NOT be used. This is
independant of any F-bit signalling in the L2-Attr Extended
Community which would still apply to unicast.
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* This document updates the procedures in [RFC8214] to include
optional use of the F-bit defined in Section 7.11 thus adding
support for flow-aware transport of EVPN-VPWS signaled
pseudowires.
19. Use of Domain-wide Common Block (DCB) Labels
The use of DCB labels as in
[I-D.ietf-bess-mvpn-evpn-aggregation-label] is RECOMMENDED in the
following cases:
* Aggregate P-multicast trees: A P-multicast tree MAY aggregate the
traffic of two or more BDs on a given ingress PE. When
aggregation is needed, DCB Labels
[I-D.ietf-bess-mvpn-evpn-aggregation-label] MAY be used in the
MPLS label field of the Inclusive Multicast Ethernet Tag routes
PMSI Tunnel Attribute. The use of DCB Labels, instead of upstream
allocated labels, can greatly reduce the number of labels that the
egress PEs need to process when P-multicast tunnel aggregation is
used in a network with a large number of BDs.
* BIER tunnels: As described in [I-D.ietf-bier-evpn], the use of
labels with BIER tunnels in EVPN networks is similar to aggregate
tunnels, since the ingress PE uses upstream allocated labels to
identify the BD. As described in [I-D.ietf-bier-evpn], DCB labels
can be allocated instead of upstream labels in the PMSI Tunnel
Attribute so that the number of labels required on the egress PEs
can be reduced.
* ESI Labels: The ESI Labels advertised with Ethernet A-D per ES
routes MAY be allocated as DCB labels in general, and are
RECOMMENDED to be allocated as DCB labels when used in combination
with P2MP/BIER tunnels.
When MP2MP tunnels are used, ESI Labels MUST be allocated from a DCB
and the same label must be used by all the PEs attached to the same
Ethernet Segment. In that way, any egress PE with local Ethernet
Segments can identify the source ES of the received BUM packets.
20. Security Considerations
Security considerations discussed in [RFC4761] and [RFC4762] apply to
this document for MAC learning in the data plane over an Attachment
Circuit (AC) and for flooding of unknown unicast and ARP messages
over the MPLS/IP core. Security considerations discussed in
[RFC4364] apply to this document for MAC learning in the control
plane over the MPLS/IP core. This section describes additional
considerations.
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As mentioned in [RFC4761], there are two aspects to achieving data
privacy and protecting against denial-of-service attacks in a VPN:
securing the control plane and protecting the forwarding path.
Compromise of the control plane could result in a PE sending customer
data belonging to some EVPN to another EVPN, or black-holing EVPN
customer data, or even sending it to an eavesdropper, none of which
are acceptable from a data privacy point of view. In addition,
compromise of the control plane could provide opportunities for
unauthorized EVPN data usage (e.g., exploiting traffic replication
within a multicast tree to amplify a denial-of-service attack based
on sending large amounts of traffic).
The mechanisms in this document use BGP for the control plane.
Hence, techniques such as those discussed in [RFC5925] help
authenticate BGP messages, making it harder to spoof updates (which
can be used to divert EVPN traffic to the wrong EVPN instance) or
withdrawals (denial-of-service attacks). In the multi-AS backbone
options (b) and (c) [RFC4364], this also means protecting the
inter-AS BGP sessions between the Autonomous System Border Routers
(ASBRs), the PEs, or the Route Reflectors.
Further discussion of security considerations for BGP may be found in
the BGP specification itself [RFC4271] and in the security analysis
for BGP [RFC4272]. The original discussion of the use of the TCP MD5
signature option to protect BGP sessions is found in [RFC5925], while
[RFC6952] includes an analysis of BGP keying and authentication
issues.
Note that [RFC5925] will not help in keeping MPLS labels private --
knowing the labels, one can eavesdrop on EVPN traffic. Such
eavesdropping additionally requires access to the data path within an
SP network. Users of VPN services are expected to take appropriate
precautions (such as encryption) to protect the data exchanged over a
VPN.
One of the requirements for protecting the data plane is that the
MPLS labels be accepted only from valid interfaces. For a PE, valid
interfaces comprise links from other routers in the PE's own AS. For
an ASBR, valid interfaces comprise links from other routers in the
ASBR's own AS, and links from other ASBRs in ASes that have instances
of a given EVPN. It is especially important in the case of multi-AS
EVPN instances that one accept EVPN packets only from valid
interfaces.
It is also important to help limit malicious traffic into a network
for an impostor MAC address. The mechanism described in Section 15.1
shows how duplicate MAC addresses can be detected and continuous
false MAC mobility can be prevented. The mechanism described in
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Section 15.2 shows how MAC addresses can be pinned to a given
Ethernet segment, such that if they appear behind any other Ethernet
segments, the traffic for those MAC addresses can be prevented from
entering the EVPN network from the other Ethernet segments.
21. IANA Considerations
This document defines a new NLRI, called "EVPN", to be carried in BGP
using multiprotocol extensions. This NLRI uses the existing AFI of
25 (L2VPN). IANA has assigned BGP EVPNs a SAFI value of 70.
IANA has allocated the following EVPN Extended Community sub-types in
[RFC7153], and this document is the only reference for them, in
addition to [RFC7432].
0x00 MAC Mobility [RFC7432]
0x01 ESI Label [RFC7432]
0x02 ES-Import Route Target [RFC7432]
This document creates a registry called "EVPN Route Types". New
registrations will be made through the "RFC Required" procedure
defined in [RFC8126]. The registry has a maximum value of 255.
Registrations carried forward from [RFC7432] are as follows:
0 Reserved [RFC7432]
1 Ethernet Auto-discovery [RFC7432]
2 MAC/IP Advertisement [RFC7432]
3 Inclusive Multicast Ethernet Tag [RFC7432]
4 Ethernet Segment [RFC7432]
This document creates a registry called "EVPN ESI Multihoming
Attributes" for the 1-octet Flags field in the ESI Label Extended
Community. New registrations will be made through the "RFC Required"
procedure defined in [RFC8126].
Initial registrations are as follows:
RED Multihomed site redundancy mode
00 = All-Active
01 = Single-Active
This document requests allocation of bit 3 in the "EVPN Layer 2
Attributes Control Flags" registry with name F:
F Flow Label MUST be present
22. References
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22.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
February 2006, <https://www.rfc-editor.org/info/rfc4360>.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <https://www.rfc-editor.org/info/rfc4364>.
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
DOI 10.17487/RFC4760, January 2007,
<https://www.rfc-editor.org/info/rfc4760>.
[RFC4761] Kompella, K., Ed. and Y. Rekhter, Ed., "Virtual Private
LAN Service (VPLS) Using BGP for Auto-Discovery and
Signaling", RFC 4761, DOI 10.17487/RFC4761, January 2007,
<https://www.rfc-editor.org/info/rfc4761>.
[RFC4762] Lasserre, M., Ed. and V. Kompella, Ed., "Virtual Private
LAN Service (VPLS) Using Label Distribution Protocol (LDP)
Signaling", RFC 4762, DOI 10.17487/RFC4762, January 2007,
<https://www.rfc-editor.org/info/rfc4762>.
[RFC7153] Rosen, E. and Y. Rekhter, "IANA Registries for BGP
Extended Communities", RFC 7153, DOI 10.17487/RFC7153,
March 2014, <https://www.rfc-editor.org/info/rfc7153>.
[RFC7432] Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
2015, <https://www.rfc-editor.org/info/rfc7432>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
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[RFC8214] Boutros, S., Sajassi, A., Salam, S., Drake, J., and J.
Rabadan, "Virtual Private Wire Service Support in Ethernet
VPN", RFC 8214, DOI 10.17487/RFC8214, August 2017,
<https://www.rfc-editor.org/info/rfc8214>.
[RFC8584] Rabadan, J., Ed., Mohanty, S., Ed., Sajassi, A., Drake,
J., Nagaraj, K., and S. Sathappan, "Framework for Ethernet
VPN Designated Forwarder Election Extensibility",
RFC 8584, DOI 10.17487/RFC8584, April 2019,
<https://www.rfc-editor.org/info/rfc8584>.
22.2. Informative References
[I-D.ietf-bess-evpn-mh-split-horizon]
Rabadan, J., Nagaraj, K., Lin, W., and A. Sajassi, "EVPN
Multi-Homing Extensions for Split Horizon Filtering", Work
in Progress, Internet-Draft, draft-ietf-bess-evpn-mh-
split-horizon-02, 15 October 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-bess-
evpn-mh-split-horizon-02>.
[I-D.ietf-bess-mvpn-evpn-aggregation-label]
Zhang, Z. J., Rosen, E. C., Lin, W., Li, Z., and I.
Wijnands, "MVPN/EVPN Tunnel Aggregation with Common
Labels", Work in Progress, Internet-Draft, draft-ietf-
bess-mvpn-evpn-aggregation-label-06, 19 April 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-bess-
mvpn-evpn-aggregation-label-06>.
[I-D.ietf-bier-evpn]
Zhang, Z. J., Przygienda, T., Sajassi, A., and J. Rabadan,
"EVPN BUM Using BIER", Work in Progress, Internet-Draft,
draft-ietf-bier-evpn-04, 2 December 2020,
<https://datatracker.ietf.org/doc/html/draft-ietf-bier-
evpn-04>.
[IEEE.802.1D_2004]
IEEE, "IEEE Standard for Local and metropolitan area
networks: Media Access Control (MAC) Bridges", IEEE
802.1D-2004, DOI 10.1109/ieeestd.2004.94569, 6 July 2004,
<http://ieeexplore.ieee.org/servlet/opac?punumber=9155>.
[IEEE.802.1Q_2014]
IEEE, "IEEE Standard for Local and metropolitan area
networks--Bridges and Bridged Networks", IEEE 802.1Q-2014,
DOI 10.1109/ieeestd.2014.6991462, 18 December 2014,
<http://ieeexplore.ieee.org/servlet/
opac?punumber=6991460>.
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[RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis",
RFC 4272, DOI 10.17487/RFC4272, January 2006,
<https://www.rfc-editor.org/info/rfc4272>.
[RFC4385] Bryant, S., Swallow, G., Martini, L., and D. McPherson,
"Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for
Use over an MPLS PSN", RFC 4385, DOI 10.17487/RFC4385,
February 2006, <https://www.rfc-editor.org/info/rfc4385>.
[RFC4664] Andersson, L., Ed. and E. Rosen, Ed., "Framework for Layer
2 Virtual Private Networks (L2VPNs)", RFC 4664,
DOI 10.17487/RFC4664, September 2006,
<https://www.rfc-editor.org/info/rfc4664>.
[RFC4684] Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk,
R., Patel, K., and J. Guichard, "Constrained Route
Distribution for Border Gateway Protocol/MultiProtocol
Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual
Private Networks (VPNs)", RFC 4684, DOI 10.17487/RFC4684,
November 2006, <https://www.rfc-editor.org/info/rfc4684>.
[RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP
Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
June 2010, <https://www.rfc-editor.org/info/rfc5925>.
[RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", RFC 6514, DOI 10.17487/RFC6514, February 2012,
<https://www.rfc-editor.org/info/rfc6514>.
[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, DOI 10.17487/RFC6790, November 2012,
<https://www.rfc-editor.org/info/rfc6790>.
[RFC6952] Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
BGP, LDP, PCEP, and MSDP Issues According to the Keying
and Authentication for Routing Protocols (KARP) Design
Guide", RFC 6952, DOI 10.17487/RFC6952, May 2013,
<https://www.rfc-editor.org/info/rfc6952>.
[RFC7117] Aggarwal, R., Ed., Kamite, Y., Fang, L., Rekhter, Y., and
C. Kodeboniya, "Multicast in Virtual Private LAN Service
(VPLS)", RFC 7117, DOI 10.17487/RFC7117, February 2014,
<https://www.rfc-editor.org/info/rfc7117>.
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[RFC7209] Sajassi, A., Aggarwal, R., Uttaro, J., Bitar, N.,
Henderickx, W., and A. Isaac, "Requirements for Ethernet
VPN (EVPN)", RFC 7209, DOI 10.17487/RFC7209, May 2014,
<https://www.rfc-editor.org/info/rfc7209>.
[RFC7991] Hoffman, P., "The "xml2rfc" Version 3 Vocabulary",
RFC 7991, DOI 10.17487/RFC7991, December 2016,
<https://www.rfc-editor.org/info/rfc7991>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8317] Sajassi, A., Ed., Salam, S., Drake, J., Uttaro, J.,
Boutros, S., and J. Rabadan, "Ethernet-Tree (E-Tree)
Support in Ethernet VPN (EVPN) and Provider Backbone
Bridging EVPN (PBB-EVPN)", RFC 8317, DOI 10.17487/RFC8317,
January 2018, <https://www.rfc-editor.org/info/rfc8317>.
[RFC8365] Sajassi, A., Ed., Drake, J., Ed., Bitar, N., Shekhar, R.,
Uttaro, J., and W. Henderickx, "A Network Virtualization
Overlay Solution Using Ethernet VPN (EVPN)", RFC 8365,
DOI 10.17487/RFC8365, March 2018,
<https://www.rfc-editor.org/info/rfc8365>.
[RFC9135] Sajassi, A., Salam, S., Thoria, S., Drake, J., and J.
Rabadan, "Integrated Routing and Bridging in Ethernet VPN
(EVPN)", RFC 9135, DOI 10.17487/RFC9135, October 2021,
<https://www.rfc-editor.org/info/rfc9135>.
[RFC9136] Rabadan, J., Ed., Henderickx, W., Drake, J., Lin, W., and
A. Sajassi, "IP Prefix Advertisement in Ethernet VPN
(EVPN)", RFC 9136, DOI 10.17487/RFC9136, October 2021,
<https://www.rfc-editor.org/info/rfc9136>.
[RFC9251] Sajassi, A., Thoria, S., Mishra, M., Patel, K., Drake, J.,
and W. Lin, "Internet Group Management Protocol (IGMP) and
Multicast Listener Discovery (MLD) Proxies for Ethernet
VPN (EVPN)", RFC 9251, DOI 10.17487/RFC9251, June 2022,
<https://www.rfc-editor.org/info/rfc9251>.
Appendix A. Acknowledgments for This Document (2022)
We would like to thank Sasha Vainshtein and Marek Hajduczenia for
reviewing the document and providing valuable comments.
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Appendix B. Contributors for This Document (2021)
In addition to the authors listed on the front page, the following
co-authors have also contributed to this document:
Appendix C. Acknowledgments from the First Edition (2015)
Special thanks to Yakov Rekhter for reviewing this document several
times and providing valuable comments, and for his very engaging
discussions on several topics of this document that helped shape this
document. We would also like to thank Pedro Marques, Kaushik Ghosh,
Nischal Sheth, Robert Raszuk, Amit Shukla, and Nadeem Mohammed for
discussions that helped shape this document. We would also like to
thank Han Nguyen for his comments and support of this work. We would
also like to thank Steve Kensil and Reshad Rahman for their reviews.
We would like to thank Jorge Rabadan for his contribution to
Section 5 of this document. We would like to thank Thomas Morin for
his review of this document and his contribution of Section 8.7.
Many thanks to Jakob Heitz for his help to improve several sections
of this document.
We would also like to thank Clarence Filsfils, Dennis Cai, Quaizar
Vohra, Kireeti Kompella, and Apurva Mehta for their contributions to
this document.
Last but not least, special thanks to Giles Heron (our WG chair) for
his detailed review of this document in preparation for WG Last Call
and for making many valuable suggestions.
C.1. Contributors from the First Edition (2015)
In addition to the authors listed on the front page, the following
co-authors have also contributed to this document:
Keyur Patel
Samer Salam
Sami Boutros
Cisco
Yakov Rekhter
Ravi Shekhar
Juniper Networks
Florin Balus
Nuage Networks
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C.2. Authors from the First Edition (2015)
Original Authors:
Ali Sajassi
Cisco
EMail: sajassi@cisco.com
Rahul Aggarwal
Arktan
EMail: raggarwa_1@yahoo.com
Nabil Bitar
Verizon Communications
EMail : nabil.n.bitar@verizon.com
Aldrin Isaac
Bloomberg
EMail: aisaac71@bloomberg.net
James Uttaro
AT&T
EMail: uttaro@att.com
John Drake
Juniper Networks
EMail: jdrake@juniper.net
Wim Henderickx
Alcatel-Lucent
EMail: wim.henderickx@alcatel-lucent.com
Authors' Addresses
Ali Sajassi (editor)
Cisco
Email: sajassi@cisco.com
Luc Andre Burdet
Cisco
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Email: lburdet@cisco.com
John Drake
Juniper
Email: jdrake@juniper.net
Jorge Rabadan
Nokia
Email: jorge.rabadan@nokia.com
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