Internet DRAFT - draft-ietf-bess-evpn-prefix-advertisement
draft-ietf-bess-evpn-prefix-advertisement
BESS Workgroup J. Rabadan, Ed.
Internet Draft W. Henderickx
Intended status: Standards Track Nokia
J. Drake
W. Lin
Juniper
A. Sajassi
Cisco
Expires: November 19, 2018 May 18, 2018
IP Prefix Advertisement in EVPN
draft-ietf-bess-evpn-prefix-advertisement-11
Abstract
The BGP MPLS-based Ethernet VPN (EVPN) [RFC7432] mechanism provides a
flexible control plane that allows intra-subnet connectivity in an
MPLS and/or NVO (Network Virtualization Overlay) [RFC7365] network.
In some networks, there is also a need for a dynamic and efficient
inter-subnet connectivity across Tenant Systems and End Devices that
can be physical or virtual and do not necessarily participate in
dynamic routing protocols. This document defines a new EVPN route
type for the advertisement of IP Prefixes and explains some use-case
examples where this new route-type is used.
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), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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."
The list of current Internet-Drafts can be accessed at
Rabadan et al. Expires November 19, 2018 [Page 1]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
This Internet-Draft will expire on November 19, 2018.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://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 Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . . 5
2.1 Inter-Subnet Connectivity Requirements in Data Centers . . . 5
2.2 The Need for the EVPN IP Prefix Route . . . . . . . . . . . 8
3. The BGP EVPN IP Prefix Route . . . . . . . . . . . . . . . . . 10
3.1 IP Prefix Route Encoding . . . . . . . . . . . . . . . . . . 11
3.2 Overlay Indexes and Recursive Lookup Resolution . . . . . . 13
4. Overlay Index Use-Cases . . . . . . . . . . . . . . . . . . . . 15
4.1 TS IP Address Overlay Index Use-Case . . . . . . . . . . . . 16
4.2 Floating IP Overlay Index Use-Case . . . . . . . . . . . . . 18
4.3 Bump-in-the-Wire Use-Case . . . . . . . . . . . . . . . . . 20
4.4 IP-VRF-to-IP-VRF Model . . . . . . . . . . . . . . . . . . . 23
4.4.1 Interface-less IP-VRF-to-IP-VRF Model . . . . . . . . . 24
4.4.2 Interface-ful IP-VRF-to-IP-VRF with SBD IRB . . . . . . 27
4.4.3 Interface-ful IP-VRF-to-IP-VRF with Unnumbered SBD IRB . 30
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 33
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 33
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 34
7.1 Normative References . . . . . . . . . . . . . . . . . . . . 34
7.2 Informative References . . . . . . . . . . . . . . . . . . . 34
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 35
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 35
10. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 36
Rabadan et al. Expires November 19, 2018 [Page 2]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
1. Introduction
[RFC7365] provides a framework for Data Center (DC) Network
Virtualization over Layer 3 and specifies that the Network
Virtualization Edge devices (NVEs) must provide layer 2 and layer 3
virtualized network services in multi-tenant DCs. [RFC8365] discusses
the use of EVPN as the technology of choice to provide layer 2 or
intra-subnet services in these DCs. This document, along with [EVPN-
INTERSUBNET], specifies the use of EVPN for layer 3 or inter-subnet
connectivity services.
[EVPN-INTERSUBNET] defines some fairly common inter-subnet forwarding
scenarios where TSes can exchange packets with TSes located in remote
subnets. In order to achieve this, [EVPN-INTERSUBNET] describes how
MAC/IPs encoded in TS RT-2 routes are not only used to populate MAC-
VRF and overlay ARP tables, but also IP-VRF tables with the encoded
TS host routes (/32 or /128). In some cases, EVPN may advertise IP
Prefixes and therefore provide aggregation in the IP-VRF tables, as
opposed to propagate individual host routes. This document
complements the scenarios described in [EVPN-INTERSUBNET] and defines
how EVPN may be used to advertise IP Prefixes. Interoperability
between EVPN and L3VPN [RFC4364] IP Prefix routes is out of the scope
of this document.
Section 2.1 describes the inter-subnet connectivity requirements in
Data Centers. Section 2.2 explains why a new EVPN route type is
required for IP Prefix advertisements. Sections 3, 4 and 5 will
describe this route type and how it is used in some specific use
cases.
1.1 Terminology
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.
AC: Attachment Circuit.
ARP: Address Resolution Protocol.
BD: Broadcast Domain. As per [RFC7432], an EVI consists of a single
or multiple BDs. In case of VLAN-bundle and VLAN-based service
models (see [RFC7432]), a BD is equivalent to an EVI. In case of
VLAN-aware bundle service model, an EVI contains multiple BDs.
Also, in this document, BD and subnet are equivalent terms.
Rabadan et al. Expires November 19, 2018 [Page 3]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
BD Route Target: refers to the Broadcast Domain assigned Route Target
[RFC4364]. In case of VLAN-aware bundle service model, all the BD
instances in the MAC-VRF share the same Route Target.
BT: Bridge Table. The instantiation of a BD in a MAC-VRF, as per
[RFC7432].
DGW: Data Center Gateway.
Ethernet A-D route: Ethernet Auto-Discovery (A-D) route, as per
[RFC7432].
Ethernet NVO tunnel: refers to Network Virtualization Overlay tunnels
with Ethernet payload. Examples of this type of tunnels are VXLAN
or GENEVE.
EVI: EVPN Instance spanning the NVE/PE devices that are participating
on that EVPN, as per [RFC7432].
EVPN: Ethernet Virtual Private Networks, as per [RFC7432].
GRE: Generic Routing Encapsulation.
GW IP: Gateway IP Address.
IPL: IP Prefix Length.
IP NVO tunnel: it refers to Network Virtualization Overlay tunnels
with IP payload (no MAC header in the payload).
IP-VRF: A VPN Routing and Forwarding table for IP routes on an
NVE/PE. The IP routes could be populated by EVPN and IP-VPN
address families. An IP-VRF is also an instantiation of a layer 3
VPN in an NVE/PE.
IRB: Integrated Routing and Bridging interface. It connects an IP-VRF
to a BD (or subnet).
MAC-VRF: A Virtual Routing and Forwarding table for Media Access
Control (MAC) addresses on an NVE/PE, as per [RFC7432]. A MAC-VRF
is also an instantiation of an EVI in an NVE/PE.
ML: MAC address length.
ND: Neighbor Discovery Protocol.
NVE: Network Virtualization Edge.
Rabadan et al. Expires November 19, 2018 [Page 4]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
GENEVE: Generic Network Virtualization Encapsulation, [GENEVE].
NVO: Network Virtualization Overlays.
RT-2: EVPN route type 2, i.e., MAC/IP advertisement route, as defined
in [RFC7432].
RT-5: EVPN route type 5, i.e., IP Prefix route. As defined in Section
3.
SBD: Supplementary Broadcast Domain. A BD that does not have any ACs,
only IRB interfaces, and it is used to provide connectivity among
all the IP-VRFs of the tenant. The SBD is only required in IP-VRF-
to-IP-VRF use-cases (see Section 4.4.).
SN: Subnet.
TS: Tenant System.
VA: Virtual Appliance.
VNI: Virtual Network Identifier. As in [RFC8365], the term is used as
a representation of a 24-bit NVO instance identifier, with the
understanding that VNI will refer to a VXLAN Network Identifier in
VXLAN, or Virtual Network Identifier in GENEVE, etc. unless it is
stated otherwise.
VTEP: VXLAN Termination End Point, as in [RFC7348].
VXLAN: Virtual Extensible LAN, as in [RFC7348].
This document also assumes familiarity with the terminology of
[RFC7432], [RFC8365] and [RFC7365].
2. Problem Statement
This Section describes the inter-subnet connectivity requirements in
Data Centers and why a specific route type to advertise IP Prefixes
is needed.
2.1 Inter-Subnet Connectivity Requirements in Data Centers
[RFC7432] is used as the control plane for a Network Virtualization
Overlay (NVO) solution in Data Centers (DC), where Network
Virtualization Edge (NVE) devices can be located in Hypervisors or
Rabadan et al. Expires November 19, 2018 [Page 5]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
Top of Rack switches (ToRs), as described in [RFC8365].
The following considerations apply to Tenant Systems (TS) that are
physical or virtual systems identified by MAC and maybe IP addresses
and connected to BDs by Attachment Circuits:
o The Tenant Systems may be Virtual Machines (VMs) that generate
traffic from their own MAC and IP.
o The Tenant Systems may be Virtual Appliance entities (VAs) that
forward traffic to/from IP addresses of different End Devices
sitting behind them.
o These VAs can be firewalls, load balancers, NAT devices, other
appliances or virtual gateways with virtual routing instances.
o These VAs do not necessarily participate in dynamic routing
protocols and hence rely on the EVPN NVEs to advertise the
routes on their behalf.
o In all these cases, the VA will forward traffic to other TSes
using its own source MAC but the source IP will be the one
associated to the End Device sitting behind or a translated IP
address (part of a public NAT pool) if the VA is performing
NAT.
o Note that the same IP address and endpoint could exist behind
two of these TSes. One example of this would be certain
appliance resiliency mechanisms, where a virtual IP or
floating IP can be owned by one of the two VAs running the
resiliency protocol (the master VA). Virtual Router Redundancy
Protocol (VRRP), RFC5798, is one particular example of this.
Another example is multi-homed subnets, i.e., the same subnet
is connected to two VAs.
o Although these VAs provide IP connectivity to VMs and subnets
behind them, they do not always have their own IP interface
connected to the EVPN NVE, e.g., layer 2 firewalls are
examples of VAs not supporting IP interfaces.
Figure 1 illustrates some of the examples described above.
Rabadan et al. Expires November 19, 2018 [Page 6]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
NVE1
+-----------+
TS1(VM)--| (BD-10) |-----+
IP1/M1 +-----------+ | DGW1
+---------+ +-------------+
| |----| (BD-10) |
SN1---+ NVE2 | | | IRB1\ |
| +-----------+ | | | (IP-VRF)|---+
SN2---TS2(VA)--| (BD-10) |-| | +-------------+ _|_
| IP2/M2 +-----------+ | VXLAN/ | ( )
IP4---+ <-+ | GENEVE | DGW2 ( WAN )
| | | +-------------+ (___)
vIP23 (floating) | |----| (BD-10) | |
| +---------+ | IRB2\ | |
SN1---+ <-+ NVE3 | | | | (IP-VRF)|---+
| IP3/M3 +-----------+ | | | +-------------+
SN3---TS3(VA)--| (BD-10) |---+ | |
| +-----------+ | |
IP5---+ | |
| |
NVE4 | | NVE5 +--SN5
+---------------------+ | | +-----------+ |
IP6------| (BD-1) | | +-| (BD-10) |--TS4(VA)--SN6
| \ | | +-----------+ |
| (IP-VRF) |--+ ESI4 +--SN7
| / \IRB3 |
|---| (BD-2) (BD-10) |
SN4| +---------------------+
Figure 1 DC inter-subnet use-cases
Where:
NVE1, NVE2, NVE3, NVE4, NVE5, DGW1 and DGW2 share the same BD for a
particular tenant. BD-10 is comprised of the collection of BD
instances defined in all the NVEs. All the hosts connected to BD-10
belong to the same IP subnet. The hosts connected to BD-10 are listed
below:
o TS1 is a VM that generates/receives traffic from/to IP1, where IP1
belongs to the BD-10 subnet.
o TS2 and TS3 are Virtual Appliances (VA) that send/receive traffic
from/to the subnets and hosts sitting behind them (SN1, SN2, SN3,
IP4 and IP5). Their IP addresses (IP2 and IP3) belong to the BD-10
subnet and they can also generate/receive traffic. When these VAs
receive packets destined to their own MAC addresses (M2 and M3)
they will route the packets to the proper subnet or host. These VAs
Rabadan et al. Expires November 19, 2018 [Page 7]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
do not support routing protocols to advertise the subnets connected
to them and can move to a different server and NVE when the Cloud
Management System decides to do so. These VAs may also support
redundancy mechanisms for some subnets, similar to VRRP, where a
floating IP is owned by the master VA and only the master VA
forwards traffic to a given subnet. E.g.,: vIP23 in Figure 1 is a
floating IP that can be owned by TS2 or TS3 depending on which
system is the master. Only the master will forward traffic to SN1.
o Integrated Routing and Bridging interfaces IRB1, IRB2 and IRB3 have
their own IP addresses that belong to the BD-10 subnet too. These
IRB interfaces connect the BD-10 subnet to Virtual Routing and
Forwarding (IP-VRF) instances that can route the traffic to other
subnets for the same tenant (within the DC or at the other end of
the WAN).
o TS4 is a layer 2 VA that provides connectivity to subnets SN5, SN6
and SN7, but does not have an IP address itself in the BD-10. TS4
is connected to a port on NVE5 assigned to Ethernet Segment
Identifier 4.
For a BD that an ingress NVE is attached to, "Overlay Index" is
defined as an identifier that the ingress EVPN NVE requires in order
to forward packets to a subnet or host in a remote subnet. As an
example, vIP23 (Figure 1) is an Overlay Index that any NVE attached
to BD-10 needs to know in order to forward packets to SN1. IRB3 IP
address is an Overlay Index required to get to SN4, and ESI4
(Ethernet Segment Identifier 4) is an Overlay Index needed to forward
traffic to SN5. In other words, the Overlay Index is a next-hop in
the overlay address space that can be an IP address, a MAC address or
an ESI. When advertised along with an IP Prefix, the Overlay Index
requires a recursive resolution to find out to what egress NVE the
EVPN packets need to be sent.
All the DC use cases in Figure 1 require inter-subnet forwarding and
therefore, the individual host routes and subnets:
a) must be advertised from the NVEs (since VAs and VMs do not
participate in dynamic routing protocols) and
b) may be associated to an Overlay Index that can be a VA IP address,
a floating IP address, a MAC address or an ESI. The Overlay Index
is further discussed in Section 3.2.
2.2 The Need for the EVPN IP Prefix Route
[RFC7432] defines a MAC/IP route (also referred as RT-2) where a MAC
Rabadan et al. Expires November 19, 2018 [Page 8]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
address can be advertised together with an IP address length and IP
address (IP). While a variable IP address length might have been used
to indicate the presence of an IP prefix in a route type 2, there are
several specific use cases in which using this route type to deliver
IP Prefixes is not suitable.
One example of such use cases is the "floating IP" example described
in Section 2.1. In this example it is needed to decouple the
advertisement of the prefixes from the advertisement of MAC address
of either M2 or M3, otherwise the solution gets highly inefficient
and does not scale.
For example, if 1,000 prefixes are advertised from M2 (using RT-2)
and the floating IP owner changes from M2 to M3, 1,000 routes would
be withdrawn from M2 and readvertise 1k routes from M3. However if a
separate route type is used, 1,000 routes can be advertised as
associated to the floating IP address (vIP23) and only one RT-2 for
advertising the ownership of the floating IP, i.e., vIP23 and M2 in
the route type 2. When the floating IP owner changes from M2 to M3, a
single RT-2 withdraw/update is required to indicate the change. The
remote DGW will not change any of the 1,000 prefixes associated to
vIP23, but will only update the ARP resolution entry for vIP23 (now
pointing at M3).
An EVPN route (type 5) for the advertisement of IP Prefixes is
described in this document. This new route type has a differentiated
role from the RT-2 route and addresses the Data Center (or NVO-based
networks in general) inter-subnet connectivity scenarios described in
this document. Using this new RT-5, an IP Prefix may be advertised
along with an Overlay Index that can be a GW IP address, a MAC or an
ESI, or without an Overlay Index, in which case the BGP next-hop will
point at the egress NVE/ASBR/ABR and the MAC in the Router's MAC
Extended Community will provide the inner MAC destination address to
be used. As discussed throughout the document, the EVPN RT-2 does not
meet the requirements for all the DC use cases, therefore this EVPN
route type 5 is required.
The EVPN route type 5 decouples the IP Prefix advertisements from the
MAC/IP route advertisements in EVPN, hence:
a) Allows the clean and clear advertisements of IPv4 or IPv6 prefixes
in an NLRI (Network Layer Reachability Information message) with
no MAC addresses.
b) Since the route type is different from the MAC/IP Advertisement
route, the current [RFC7432] procedures do not need to be
modified.
Rabadan et al. Expires November 19, 2018 [Page 9]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
c) Allows a flexible implementation where the prefix can be linked to
different types of Overlay/Underlay Indexes: overlay IP address,
overlay MAC addresses, overlay ESI, underlay BGP next-hops, etc.
d) An EVPN implementation not requiring IP Prefixes can simply
discard them by looking at the route type value.
The following Sections describe how EVPN is extended with a route
type for the advertisement of IP prefixes and how this route is used
to address the inter-subnet connectivity requirements existing in the
Data Center.
3. The BGP EVPN IP Prefix Route
The BGP EVPN NLRI as defined in [RFC7432] is shown below:
+-----------------------------------+
| Route Type (1 octet) |
+-----------------------------------+
| Length (1 octet) |
+-----------------------------------+
| Route Type specific (variable) |
+-----------------------------------+
Figure 2 BGP EVPN NLRI
This document defines an additional route type (RT-5) in the IANA
EVPN Route Types registry [EVPNRouteTypes], to be used for the
advertisement of EVPN routes using IP Prefixes:
Value: 5
Description: IP Prefix Route
According to Section 5.4 in [RFC7606], a node that doesn't recognize
the Route Type 5 (RT-5) will ignore it. Therefore an NVE following
this document can still be attached to a BD where an NVE ignoring RT-
5s is attached to. Regular [RFC7432] procedures would apply in that
case for both NVEs. In case two or more NVEs are attached to
different BDs of the same tenant, they MUST support RT-5 for the
proper Inter-Subnet Forwarding operation of the tenant.
The detailed encoding of this route and associated procedures are
described in the following Sections.
Rabadan et al. Expires November 19, 2018 [Page 10]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
3.1 IP Prefix Route Encoding
An IP Prefix Route Type for IPv4 has the Length field set to 34 and
consists of the following fields:
+---------------------------------------+
| RD (8 octets) |
+---------------------------------------+
|Ethernet Segment Identifier (10 octets)|
+---------------------------------------+
| Ethernet Tag ID (4 octets) |
+---------------------------------------+
| IP Prefix Length (1 octet, 0 to 32) |
+---------------------------------------+
| IP Prefix (4 octets) |
+---------------------------------------+
| GW IP Address (4 octets) |
+---------------------------------------+
| MPLS Label (3 octets) |
+---------------------------------------+
Figure 3 EVPN IP Prefix route NLRI for IPv4
An IP Prefix Route Type for IPv6 has the Length field set to 58 and
consists of the following fields:
+---------------------------------------+
| RD (8 octets) |
+---------------------------------------+
|Ethernet Segment Identifier (10 octets)|
+---------------------------------------+
| Ethernet Tag ID (4 octets) |
+---------------------------------------+
| IP Prefix Length (1 octet, 0 to 128) |
+---------------------------------------+
| IP Prefix (16 octets) |
+---------------------------------------+
| GW IP Address (16 octets) |
+---------------------------------------+
| MPLS Label (3 octets) |
+---------------------------------------+
Figure 4 EVPN IP Prefix route NLRI for IPv6
Where:
Rabadan et al. Expires November 19, 2018 [Page 11]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
o The Length field of the BGP EVPN NLRI for an EVPN IP Prefix route
MUST be either 34 (if IPv4 addresses are carried) or 58 (if IPv6
addresses are carried). The IP Prefix and Gateway IP Address MUST
be from the same IP address family.
o Route Distinguisher (RD) and Ethernet Tag ID MUST be used as
defined in [RFC7432] and [RFC8365]. In particular, the RD is unique
per MAC-VRF (or IP-VRF). The MPLS Label field is set to either an
MPLS label or a VNI, as described in [RFC8365] for other EVPN route
types.
o The Ethernet Segment Identifier MUST be a non-zero 10-octet
identifier if the ESI is used as an Overlay Index (see the
definition of Overlay Index in Section 3.2). It MUST be all bytes
zero otherwise. The ESI format is described in [RFC7432].
o The IP Prefix Length can be set to a value between 0 and 32 (bits)
for IPv4 and between 0 and 128 for IPv6, and specifies the number
of bits in the Prefix. The value MUST NOT be greater than 128.
o The IP Prefix is a 4 or 16-octet field (IPv4 or IPv6).
o The GW (Gateway) IP Address field is a 4 or 16-octet field (IPv4 or
IPv6), and will encode a valid IP address as an Overlay Index for
the IP Prefixes. The GW IP field MUST be all bytes zero if it is
not used as an Overlay Index. Refer to Section 3.2 for the
definition and use of the Overlay Index.
o The MPLS Label field is encoded as 3 octets, where the high-order
20 bits contain the label value, as per [RFC7432]. When sending,
the label value SHOULD be zero if recursive resolution based on
overlay index is used. If the received MPLS Label value is zero,
the route MUST contain an Overlay Index and the ingress NVE/PE MUST
do recursive resolution to find the egress NVE/PE. If the received
Label is zero and the route does not contain an Overlay Index, it
MUST be treat-as-withdraw [RFC7606].
The RD, Ethernet Tag ID, IP Prefix Length and IP Prefix are part of
the route key used by BGP to compare routes. The rest of the fields
are not part of the route key.
An IP Prefix Route MAY be sent along with a Router's MAC Extended
Community (defined in [EVPN-INTERSUBNET]) to carry the MAC address
that is used as the overlay index. Note that the MAC address may be
that of an TS.
As described in Section 3.2, certain data combinations in a received
routes would imply a "treat-as-withdraw" handling of the route
Rabadan et al. Expires November 19, 2018 [Page 12]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
[RFC7606].
3.2 Overlay Indexes and Recursive Lookup Resolution
RT-5 routes support recursive lookup resolution through the use of
Overlay Indexes as follows:
o An Overlay Index can be an ESI, IP address in the address space of
the tenant or MAC address and it is used by an NVE as the next-hop
for a given IP Prefix. An Overlay Index always needs a recursive
route resolution on the NVE/PE that installs the RT-5 into one of
its IP-VRFs, so that the NVE knows to which egress NVE/PE it needs
to forward the packets. It is important to note that recursive
resolution of the Overlay Index applies upon installation into an
IP-VRF, and not upon BGP propagation (for instance, on an ASBR).
Also, as a result of the recursive resolution, the egress NVE/PE is
not necessarily the same NVE that originated the RT-5.
o The Overlay Index is indicated along with the RT-5 in the ESI
field, GW IP field or Router's MAC Extended Community, depending on
whether the IP Prefix next-hop is an ESI, IP address or MAC address
in the tenant space. The Overlay Index for a given IP Prefix is set
by local policy at the NVE that originates an RT-5 for that IP
Prefix (typically managed by the Cloud Management System).
o In order to enable the recursive lookup resolution at the ingress
NVE, an NVE that is a possible egress NVE for a given Overlay Index
must originate a route advertising itself as the BGP next hop on
the path to the system denoted by the Overlay Index. For instance:
. If an NVE receives an RT-5 that specifies an Overlay Index, the
NVE cannot use the RT-5 in its IP-VRF unless (or until) it can
recursively resolve the Overlay Index.
. If the RT-5 specifies an ESI as the Overlay Index, recursive
resolution can only be done if the NVE has received and installed
an RT-1 (Auto-Discovery per-EVI) route specifying that ESI.
. If the RT-5 specifies a GW IP address as the Overlay Index,
recursive resolution can only be done if the NVE has received and
installed an RT-2 (MAC/IP route) specifying that IP address in
the IP address field of its NLRI.
. If the RT-5 specifies a MAC address as the Overlay Index,
recursive resolution can only be done if the NVE has received and
installed an RT-2 (MAC/IP route) specifying that MAC address in
the MAC address field of its NLRI.
Note that the RT-1 or RT-2 routes needed for the recursive
resolution may arrive before or after the given RT-5 route.
Rabadan et al. Expires November 19, 2018 [Page 13]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
o Irrespective of the recursive resolution, if there is no IGP or BGP
route to the BGP next-hop of an RT-5, BGP MUST NOT install the RT-5
even if the Overlay Index can be resolved.
o The ESI and GW IP fields may both be zero at the same time.
However, they MUST NOT both be non-zero at the same time. A route
containing a non-zero GW IP and a non-zero ESI (at the same time)
SHOULD be treat-as-withdraw [RFC7606].
o If either the ESI or GW IP are non-zero, then the non-zero one is
the Overlay Index, regardless of whether the Router's MAC Extended
Community is present or the value of the Label. In case the GW IP
is the Overlay Index (hence ESI is zero), the Router's MAC Extended
Community is ignored if present.
o A route where ESI, GW IP, MAC and Label are all zero at the same
time SHOULD be treat-as-withdraw.
The indirection provided by the Overlay Index and its recursive
lookup resolution is required to achieve fast convergence in case of
a failure of the object represented by the Overlay Index (see the
example described in Section 2.2).
Table 1 shows the different RT-5 field combinations allowed by this
specification and what Overlay Index must be used by the receiving
NVE/PE in each case. Those cases where there is no Overlay Index, are
indicated as "None" in Table 1. If there is no Overlay Index the
receiving NVE/PE will not perform any recursive resolution, and the
actual next-hop is given by the RT-5's BGP next-hop.
+----------+----------+----------+------------+----------------+
| ESI | GW IP | MAC* | Label | Overlay Index |
|--------------------------------------------------------------|
| Non-Zero | Zero | Zero | Don't Care | ESI |
| Non-Zero | Zero | Non-Zero | Don't Care | ESI |
| Zero | Non-Zero | Zero | Don't Care | GW IP |
| Zero | Zero | Non-Zero | Zero | MAC |
| Zero | Zero | Non-Zero | Non-Zero | MAC or None** |
| Zero | Zero | Zero | Non-Zero | None*** |
+----------+----------+----------+------------+----------------+
Table 1 - RT-5 fields and Indicated Overlay Index
Table NOTES:
* MAC with Zero value means no Router's MAC extended community is
present along with the RT-5. Non-Zero indicates that the extended
community is present and carries a valid MAC address. The
Rabadan et al. Expires November 19, 2018 [Page 14]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
encoding of a MAC address MUST be the 6-octet MAC address
specified by [802.1Q] and [802.1D-REV]. Examples of invalid MAC
addresses are broadcast or multicast MAC addresses. The route
MUST be treat-as-withdraw in case of an invalid MAC address. The
presence of the Router's MAC extended community alone is not
enough to indicate the use of the MAC address as the Overlay
Index, since the extended community can be used for other
purposes.
** In this case, the Overlay Index may be the RT-5's MAC address or
None, depending on the local policy of the receiving NVE/PE. Note
that the advertising NVE/PE that sets the Overlay Index SHOULD
advertise an RT-2 for the MAC Overlay Index if there are
receiving NVE/PEs configured to use the MAC as the Overlay Index.
This case in Table 1 is used in the IP-VRF-to-IP-VRF
implementations described in 4.4.1 and 4.4.3. The support of a
MAC Overlay Index in this model is OPTIONAL.
*** The Overlay Index is None. This is a special case used for IP-
VRF-to-IP-VRF where the NVE/PEs are connected by IP NVO tunnels
as opposed to Ethernet NVO tunnels.
If the combination of ESI, GW IP, MAC and Label in the receiving RT-5
is different than the combinations shown in Table 1, the router will
process the route as per the rules described at the beginning of this
Section (3.2).
Table 2 shows the different inter-subnet use-cases described in this
document and the corresponding coding of the Overlay Index in the
route type 5 (RT-5).
+---------+---------------------+----------------------------+
| Section | Use-case | Overlay Index in the RT-5 |
+-------------------------------+----------------------------+
| 4.1 | TS IP address | GW IP |
| 4.2 | Floating IP address | GW IP |
| 4.3 | "Bump in the wire" | ESI or MAC |
| 4.4 | IP-VRF-to-IP-VRF | GW IP, MAC or None |
+---------+---------------------+----------------------------+
Table 2 - Use-cases and Overlay Indexes for Recursive Resolution
The above use-cases are representative of the different Overlay
Indexes supported by RT-5 (GW IP, ESI, MAC or None).
4. Overlay Index Use-Cases
Rabadan et al. Expires November 19, 2018 [Page 15]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
This Section describes some use-cases for the Overlay Index types
used with the IP Prefix route. Although the examples use IPv4
Prefixes and subnets, the descriptions of the RT-5 are valid for the
same cases with IPv6, only replacing the IP Prefixes, IPL and GW IP
by the corresponding IPv6 values.
4.1 TS IP Address Overlay Index Use-Case
Figure 5 illustrates an example of inter-subnet forwarding for
subnets sitting behind Virtual Appliances (on TS2 and TS3).
IP4---+ NVE2 DGW1
| +-----------+ +---------+ +-------------+
SN2---TS2(VA)--| (BD-10) |-| |----| (BD-10) |
| IP2/M2 +-----------+ | | | IRB1\ |
-+---+ | | | (IP-VRF)|---+
| | | +-------------+ _|_
SN1 | VXLAN/ | ( )
| | GENEVE | DGW2 ( WAN )
-+---+ NVE3 | | +-------------+ (___)
| IP3/M3 +-----------+ | |----| (BD-10) | |
SN3---TS3(VA)--| (BD-10) |-| | | IRB2\ | |
| +-----------+ +---------+ | (IP-VRF)|---+
IP5---+ +-------------+
Figure 5 TS IP address use-case
An example of inter-subnet forwarding between subnet SN1, which uses
a 24 bit IP prefix (written as SN1/24 in future), and a subnet
sitting in the WAN is described below. NVE2, NVE3, DGW1 and DGW2 are
running BGP EVPN. TS2 and TS3 do not participate in dynamic routing
protocols, and they only have a static route to forward the traffic
to the WAN. SN1/24 is dual-homed to NVE2 and NVE3.
In this case, a GW IP is used as an Overlay Index. Although a
different Overlay Index type could have been used, this use-case
assumes that the operator knows the VA's IP addresses beforehand,
whereas the VA's MAC address is unknown and the VA's ESI is zero.
Because of this, the GW IP is the suitable Overlay Index to be used
with the RT-5s. The NVEs know the GW IP to be used for a given Prefix
by policy.
(1) NVE2 advertises the following BGP routes on behalf of TS2:
o Route type 2 (MAC/IP route) containing: ML=48 (MAC Address
Length), M=M2 (MAC Address), IPL=32 (IP Prefix Length), IP=IP2
and [RFC5512] BGP Encapsulation Extended Community with the
corresponding Tunnel type. The MAC and IP addresses may be
Rabadan et al. Expires November 19, 2018 [Page 16]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
learned via ARP snooping.
o Route type 5 (IP Prefix route) containing: IPL=24, IP=SN1,
ESI=0, GW IP address=IP2. The prefix and GW IP are learned by
policy.
(2) Similarly, NVE3 advertises the following BGP routes on behalf of
TS3:
o Route type 2 (MAC/IP route) containing: ML=48, M=M3, IPL=32,
IP=IP3 (and BGP Encapsulation Extended Community).
o Route type 5 (IP Prefix route) containing: IPL=24, IP=SN1,
ESI=0, GW IP address=IP3.
(3) DGW1 and DGW2 import both received routes based on the Route
Targets:
o Based on the BD-10 Route Target in DGW1 and DGW2, the MAC/IP
route is imported and M2 is added to the BD-10 along with its
corresponding tunnel information. For instance, if VXLAN is
used, the VTEP will be derived from the MAC/IP route BGP next-
hop and VNI from the MPLS Label1 field. IP2 - M2 is added to
the ARP table. Similarly, M3 is added to BD-10 and IP3 - M3 to
the ARP table.
o Based on the BD-10 Route Target in DGW1 and DGW2, the IP
Prefix route is also imported and SN1/24 is added to the IP-
VRF with Overlay Index IP2 pointing at the local BD-10. In
this example, it is assumed that the RT-5 from NVE2 is
preferred over the RT-5 from NVE3. If both routes were equally
preferable and ECMP enabled, SN1/24 would also be added to the
routing table with Overlay Index IP3.
(4) When DGW1 receives a packet from the WAN with destination IPx,
where IPx belongs to SN1/24:
o A destination IP lookup is performed on the DGW1 IP-VRF
routing table and Overlay Index=IP2 is found. Since IP2 is an
Overlay Index a recursive route resolution is required for
IP2.
o IP2 is resolved to M2 in the ARP table, and M2 is resolved to
the tunnel information given by the BD FIB (e.g., remote VTEP
and VNI for the VXLAN case).
o The IP packet destined to IPx is encapsulated with:
Rabadan et al. Expires November 19, 2018 [Page 17]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
. Source inner MAC = IRB1 MAC.
. Destination inner MAC = M2.
. Tunnel information provided by the BD (VNI, VTEP IPs and
MACs for the VXLAN case).
(5) When the packet arrives at NVE2:
o Based on the tunnel information (VNI for the VXLAN case), the
BD-10 context is identified for a MAC lookup.
o Encapsulation is stripped off and based on a MAC lookup
(assuming MAC forwarding on the egress NVE), the packet is
forwarded to TS2, where it will be properly routed.
(6) Should TS2 move from NVE2 to NVE3, MAC Mobility procedures will
be applied to the MAC route IP2/M2, as defined in [RFC7432].
Route type 5 prefixes are not subject to MAC mobility procedures,
hence no changes in the DGW IP-VRF routing table will occur for
TS2 mobility, i.e., all the prefixes will still be pointing at
IP2 as Overlay Index. There is an indirection for e.g., SN1/24,
which still points at Overlay Index IP2 in the routing table, but
IP2 will be simply resolved to a different tunnel, based on the
outcome of the MAC mobility procedures for the MAC/IP route
IP2/M2.
Note that in the opposite direction, TS2 will send traffic based on
its static-route next-hop information (IRB1 and/or IRB2), and regular
EVPN procedures will be applied.
4.2 Floating IP Overlay Index Use-Case
Sometimes Tenant Systems (TS) work in active/standby mode where an
upstream floating IP - owned by the active TS - is used as the
Overlay Index to get to some subnets behind. This redundancy mode,
already introduced in Section 2.1 and 2.2, is illustrated in Figure
6.
Rabadan et al. Expires November 19, 2018 [Page 18]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
NVE2 DGW1
+-----------+ +---------+ +-------------+
+---TS2(VA)--| (BD-10) |-| |----| (BD-10) |
| IP2/M2 +-----------+ | | | IRB1\ |
| <-+ | | | (IP-VRF)|---+
| | | | +-------------+ _|_
SN1 vIP23 (floating) | VXLAN/ | ( )
| | | GENEVE | DGW2 ( WAN )
| <-+ NVE3 | | +-------------+ (___)
| IP3/M3 +-----------+ | |----| (BD-10) | |
+---TS3(VA)--| (BD-10) |-| | | IRB2\ | |
+-----------+ +---------+ | (IP-VRF)|---+
+-------------+
Figure 6 Floating IP Overlay Index for redundant TS
In this use-case, a GW IP is used as an Overlay Index for the same
reasons as in 4.1. However, this GW IP is a floating IP that belongs
to the active TS. Assuming TS2 is the active TS and owns vIP23:
(1) NVE2 advertises the following BGP routes for TS2:
o Route type 2 (MAC/IP route) containing: ML=48, M=M2, IPL=32,
IP=vIP23 (and BGP Encapsulation Extended Community). The MAC
and IP addresses may be learned via ARP snooping.
o Route type 5 (IP Prefix route) containing: IPL=24, IP=SN1,
ESI=0, GW IP address=vIP23. The prefix and GW IP are learned
by policy.
(2) NVE3 advertises the following BGP route for TS3 (it does not
advertise an RT-2 for vIP23/M3):
o Route type 5 (IP Prefix route) containing: IPL=24, IP=SN1,
ESI=0, GW IP address=vIP23. The prefix and GW IP are learned
by policy.
(3) DGW1 and DGW2 import both received routes based on the Route
Target:
o M2 is added to the BD-10 FIB along with its corresponding
tunnel information. For the VXLAN use case, the VTEP will be
derived from the MAC/IP route BGP next-hop and VNI from the
VNI field. vIP23 - M2 is added to the ARP table.
o SN1/24 is added to the IP-VRF in DGW1 and DGW2 with Overlay
index vIP23 pointing at M2 in the local BD-10.
Rabadan et al. Expires November 19, 2018 [Page 19]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
(4) When DGW1 receives a packet from the WAN with destination IPx,
where IPx belongs to SN1/24:
o A destination IP lookup is performed on the DGW1 IP-VRF
routing table and Overlay Index=vIP23 is found. Since vIP23 is
an Overlay Index, a recursive route resolution for vIP23 is
required.
o vIP23 is resolved to M2 in the ARP table, and M2 is resolved
to the tunnel information given by the BD (remote VTEP and VNI
for the VXLAN case).
o The IP packet destined to IPx is encapsulated with:
. Source inner MAC = IRB1 MAC.
. Destination inner MAC = M2.
. Tunnel information provided by the BD FIB (VNI, VTEP IPs
and MACs for the VXLAN case).
(5) When the packet arrives at NVE2:
o Based on the tunnel information (VNI for the VXLAN case), the
BD-10 context is identified for a MAC lookup.
o Encapsulation is stripped off and based on a MAC lookup
(assuming MAC forwarding on the egress NVE), the packet is
forwarded to TS2, where it will be properly routed.
(6) When the redundancy protocol running between TS2 and TS3 appoints
TS3 as the new active TS for SN1, TS3 will now own the floating
vIP23 and will signal this new ownership, using a gratuitous ARP
REPLY message (explained in [RFC5227]) or similar. Upon receiving
the new owner's notification, NVE3 will issue a route type 2 for
M3-vIP23 and NVE2 will withdraw the RT-2 for M2-vIP23. DGW1 and
DGW2 will update their ARP tables with the new MAC resolving the
floating IP. No changes are made in the IP-VRF routing table.
4.3 Bump-in-the-Wire Use-Case
Figure 7 illustrates an example of inter-subnet forwarding for an IP
Prefix route that carries a subnet SN1. In this use-case, TS2 and TS3
are layer 2 VA devices without any IP address that can be included as
an Overlay Index in the GW IP field of the IP Prefix route. Their MAC
addresses are M2 and M3 respectively and are connected to BD-10. Note
that IRB1 and IRB2 (in DGW1 and DGW2 respectively) have IP addresses
Rabadan et al. Expires November 19, 2018 [Page 20]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
in a subnet different than SN1.
NVE2 DGW1
M2 +-----------+ +---------+ +-------------+
+---TS2(VA)--| (BD-10) |-| |----| (BD-10) |
| ESI23 +-----------+ | | | IRB1\ |
| + | | | (IP-VRF)|---+
| | | | +-------------+ _|_
SN1 | | VXLAN/ | ( )
| | | GENEVE | DGW2 ( WAN )
| + NVE3 | | +-------------+ (___)
| ESI23 +-----------+ | |----| (BD-10) | |
+---TS3(VA)--| (BD-10) |-| | | IRB2\ | |
M3 +-----------+ +---------+ | (IP-VRF)|---+
+-------------+
Figure 7 Bump-in-the-wire use-case
Since neither TS2 nor TS3 can participate in any dynamic routing
protocol and have no IP address assigned, there are two potential
Overlay Index types that can be used when advertising SN1:
a) an ESI, i.e., ESI23, that can be provisioned on the attachment
ports of NVE2 and NVE3, as shown in Figure 7.
b) or the VA's MAC address, that can be added to NVE2 and NVE3 by
policy.
The advantage of using an ESI as Overlay Index as opposed to the VA's
MAC address, is that the forwarding to the egress NVE can be done
purely based on the state of the AC in the ES (notified by the
Ethernet A-D per-EVI route) and all the EVPN multi-homing redundancy
mechanisms can be reused. For instance, the [RFC7432] mass-withdrawal
mechanism for fast failure detection and propagation can be used.
This Section assumes that an ESI Overlay Index is used in this use-
case but it does not prevent the use of the VA's MAC address as an
Overlay Index. If a MAC is used as Overlay Index, the control plane
must follow the procedures described in Section 4.4.3.
The model supports VA redundancy in a similar way to the one
described in Section 4.2 for the floating IP Overlay Index use-case,
except that it uses the EVPN Ethernet A-D per-EVI route instead of
the MAC advertisement route to advertise the location of the Overlay
Index. The procedure is explained below:
(1) Assuming TS2 is the active TS in ESI23, NVE2 advertises the
following BGP routes:
Rabadan et al. Expires November 19, 2018 [Page 21]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
o Route type 1 (Ethernet A-D route for BD-10) containing:
ESI=ESI23 and the corresponding tunnel information (VNI
field), as well as the BGP Encapsulation Extended Community as
per [RFC8365].
o Route type 5 (IP Prefix route) containing: IPL=24, IP=SN1,
ESI=ESI23, GW IP address=0. The Router's MAC Extended
Community defined in [EVPN-INTERSUBNET] is added and carries
the MAC address (M2) associated to the TS behind which SN1
sits. M2 may be learned by policy, however the MAC in the
Extended Community is preferred if sent with the route.
(2) NVE3 advertises the following BGP route for TS3 (no AD per-EVI
route is advertised):
o Route type 5 (IP Prefix route) containing: IPL=24, IP=SN1,
ESI=23, GW IP address=0. The Router's MAC Extended Community
is added and carries the MAC address (M3) associated to the TS
behind which SN1 sits. M3 may be learned by policy, however
the MAC in the Extended Community is preferred if sent with
the route.
(3) DGW1 and DGW2 import the received routes based on the Route
Target:
o The tunnel information to get to ESI23 is installed in DGW1
and DGW2. For the VXLAN use case, the VTEP will be derived
from the Ethernet A-D route BGP next-hop and VNI from the
VNI/VSID field (see [RFC8365]).
o The RT-5 coming from the NVE that advertised the RT-1 is
selected and SN1/24 is added to the IP-VRF in DGW1 and DGW2
with Overlay Index ESI23 and MAC = M2.
(4) When DGW1 receives a packet from the WAN with destination IPx,
where IPx belongs to SN1/24:
o A destination IP lookup is performed on the DGW1 IP-VRF
routing table and Overlay Index=ESI23 is found. Since ESI23 is
an Overlay Index, a recursive route resolution is required to
find the egress NVE where ESI23 resides.
o The IP packet destined to IPx is encapsulated with:
. Source inner MAC = IRB1 MAC.
. Destination inner MAC = M2 (this MAC will be obtained
from the Router's MAC Extended Community received along
Rabadan et al. Expires November 19, 2018 [Page 22]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
with the RT-5 for SN1). Note that the Router's MAC
Extended Community is used in this case to carry the TS'
MAC address, as opposed to the NVE/PE's MAC address.
. Tunnel information for the NVO tunnel is provided by the
Ethernet A-D route per-EVI for ESI23 (VNI and VTEP IP for
the VXLAN case).
(5) When the packet arrives at NVE2:
o Based on the tunnel demultiplexer information (VNI for the
VXLAN case), the BD-10 context is identified for a MAC lookup
(assuming MAC-based disposition model [RFC7432]) or the VNI
may directly identify the egress interface (for a MPLS-based
disposition model, which in this context is a VNI-based
disposition model).
o Encapsulation is stripped off and based on a MAC lookup
(assuming MAC forwarding on the egress NVE) or a VNI lookup
(in case of VNI forwarding), the packet is forwarded to TS2,
where it will be forwarded to SN1.
(6) If the redundancy protocol running between TS2 and TS3 follows an
active/standby model and there is a failure, appointing TS3 as
the new active TS for SN1, TS3 will now own the connectivity to
SN1 and will signal this new ownership. Upon receiving the new
owner's notification, NVE3's AC will become active and issue a
route type 1 for ESI23, whereas NVE2 will withdraw its Ethernet
A-D route for ESI23. DGW1 and DGW2 will update their tunnel
information to resolve ESI23. The destination inner MAC will be
changed to M3.
4.4 IP-VRF-to-IP-VRF Model
This use-case is similar to the scenario described in "IRB forwarding
on NVEs for Tenant Systems" in [EVPN-INTERSUBNET], however the new
requirement here is the advertisement of IP Prefixes as opposed to
only host routes.
In the examples described in Sections 4.1, 4.2 and 4.3, the BD
instance can connect IRB interfaces and any other Tenant Systems
connected to it. EVPN provides connectivity for:
1. Traffic destined to the IRB or TS IP interfaces as well as
2. Traffic destined to IP subnets sitting behind the TS, e.g., SN1 or
SN2.
Rabadan et al. Expires November 19, 2018 [Page 23]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
In order to provide connectivity for (1), MAC/IP routes (RT-2) are
needed so that IRB or TS MACs and IPs can be distributed.
Connectivity type (2) is accomplished by the exchange of IP Prefix
routes (RT-5) for IPs and subnets sitting behind certain Overlay
Indexes, e.g., GW IP or ESI or TS MAC.
In some cases, IP Prefix routes may be advertised for subnets and IPs
sitting behind an IRB. This use-case is referred to as the "IP-VRF-
to-IP-VRF" model.
[EVPN-INTERSUBNET] defines an asymmetric IRB model and a symmetric
IRB model, based on the required lookups at the ingress and egress
NVE: the asymmetric model requires an IP lookup and a MAC lookup at
the ingress NVE, whereas only a MAC lookup is needed at the egress
NVE; the symmetric model requires IP and MAC lookups at both, ingress
and egress NVE. From that perspective, the IP-VRF-to-IP-VRF use-case
described in this Section is a symmetric IRB model.
Note that, in an IP-VRF-to-IP-VRF scenario, out of the many subnets
that a tenant may have, it may be the case that only a few are
attached to a given NVE/PE's IP-VRF. In order to provide inter-subnet
connectivity among the set of NVE/PEs where the tenant is connected,
a new SBD is created on all of them if recursive resolution is
needed. This SBD is instantiated as a regular BD (with no ACs) in
each NVE/PE and has an IRB interface that connects the SBD to the IP-
VRF. The IRB interface's IP or MAC address is used as the overlay
index for recursive resolution.
Depending on the existence and characteristics of the SBD and IRB
interfaces for the IP-VRFs, there are three different IP-VRF-to-IP-
VRF scenarios identified and described in this document:
1) Interface-less model: no SBD and no overlay indexes required.
2) Interface-ful with SBD IRB model: it requires SBD, as well as GW
IP addresses as overlay indexes.
3) Interface-ful with unnumbered SBD IRB model: it requires SBD, as
well as MAC addresses as overlay indexes.
Inter-subnet IP multicast is outside the scope of this document.
4.4.1 Interface-less IP-VRF-to-IP-VRF Model
Figure 8 will be used for the description of this model.
Rabadan et al. Expires November 19, 2018 [Page 24]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
NVE1(M1)
+------------+
IP1+----| (BD-1) | DGW1(M3)
| \ | +---------+ +--------+
| (IP-VRF)|----| |-|(IP-VRF)|----+
| / | | | +--------+ |
+---| (BD-2) | | | _+_
| +------------+ | | ( )
SN1| | VXLAN/ | ( WAN )--H1
| NVE2(M2) | GENEVE/| (___)
| +------------+ | MPLS | +
+---| (BD-2) | | | DGW2(M4) |
| \ | | | +--------+ |
| (IP-VRF)|----| |-|(IP-VRF)|----+
| / | +---------+ +--------+
SN2+----| (BD-3) |
+------------+
Figure 8 Interface-less IP-VRF-to-IP-VRF model
In this case:
a) The NVEs and DGWs must provide connectivity between hosts in SN1,
SN2, IP1 and hosts sitting at the other end of the WAN, for
example, H1. It is assumed that the DGWs import/export IP and/or
VPN-IP routes from/to the WAN.
b) The IP-VRF instances in the NVE/DGWs are directly connected
through NVO tunnels, and no IRBs and/or BD instances are
instantiated to connect the IP-VRFs.
c) The solution must provide layer 3 connectivity among the IP-VRFs
for Ethernet NVO tunnels, for instance, VXLAN or GENEVE.
d) The solution may provide layer 3 connectivity among the IP-VRFs
for IP NVO tunnels, for example, GENEVE (with IP payload).
In order to meet the above requirements, the EVPN route type 5 will
be used to advertise the IP Prefixes, along with the Router's MAC
Extended Community as defined in [EVPN-INTERSUBNET] if the
advertising NVE/DGW uses Ethernet NVO tunnels. Each NVE/DGW will
advertise an RT-5 for each of its prefixes with the following fields:
o RD as per [RFC7432].
Rabadan et al. Expires November 19, 2018 [Page 25]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
o Ethernet Tag ID=0.
o IP Prefix Length and IP address, as explained in the previous
Sections.
o GW IP address=0.
o ESI=0
o MPLS label or VNI corresponding to the IP-VRF.
Each RT-5 will be sent with a Route Target identifying the tenant
(IP-VRF) and may be sent with two BGP extended communities:
o The first one is the BGP Encapsulation Extended Community, as
per [RFC5512], identifying the tunnel type.
o The second one is the Router's MAC Extended Community as per
[EVPN-INTERSUBNET] containing the MAC address associated to
the NVE advertising the route. This MAC address identifies the
NVE/DGW and MAY be reused for all the IP-VRFs in the NVE. The
Router's MAC Extended Community must be sent if the route is
associated to an Ethernet NVO tunnel, for instance, VXLAN. If
the route is associated to an IP NVO tunnel, for instance
GENEVE with IP payload, the Router's MAC Extended Community
should not be sent.
The following example illustrates the procedure to advertise and
forward packets to SN1/24 (IPv4 prefix advertised from NVE1):
(1) NVE1 advertises the following BGP route:
o Route type 5 (IP Prefix route) containing:
. IPL=24, IP=SN1, Label=10.
. GW IP= set to 0.
. [RFC5512] BGP Encapsulation Extended Community.
. Router's MAC Extended Community that contains M1.
. Route Target identifying the tenant (IP-VRF).
(2) DGW1 imports the received routes from NVE1:
o DGW1 installs SN1/24 in the IP-VRF identified by the RT-5
Route Target.
Rabadan et al. Expires November 19, 2018 [Page 26]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
o Since GW IP=ESI=0, the Label is a non-zero value and the local
policy indicates this interface-less model, DGW1 will use the
Label and next-hop of the RT-5, as well as the MAC address
conveyed in the Router's MAC Extended Community (as inner
destination MAC address) to set up the forwarding state and
later encapsulate the routed IP packets.
(3) When DGW1 receives a packet from the WAN with destination IPx,
where IPx belongs to SN1/24:
o A destination IP lookup is performed on the DGW1 IP-VRF
routing table. The lookup yields SN1/24.
o Since the RT-5 for SN1/24 had a GW IP=ESI=0, a non-zero Label
and next-hop and the model is interface-less, DGW1 will not
need a recursive lookup to resolve the route.
o The IP packet destined to IPx is encapsulated with: Source
inner MAC = DGW1 MAC, Destination inner MAC = M1, Source outer
IP (tunnel source IP) = DGW1 IP, Destination outer IP (tunnel
destination IP) = NVE1 IP. The Source and Destination inner
MAC addresses are not needed if IP NVO tunnels are used.
(4) When the packet arrives at NVE1:
o NVE1 will identify the IP-VRF for an IP lookup based on the
Label (the Destination inner MAC is not needed to identify the
IP-VRF).
o An IP lookup is performed in the routing context, where SN1
turns out to be a local subnet associated to BD-2. A
subsequent lookup in the ARP table and the BD FIB will provide
the forwarding information for the packet in BD-2.
The model described above is called Interface-less model since the
IP-VRFs are connected directly through tunnels and they don't require
those tunnels to be terminated in SBDs instead, as in Sections 4.4.2
or 4.4.3.
4.4.2 Interface-ful IP-VRF-to-IP-VRF with SBD IRB
Figure 9 will be used for the description of this model.
Rabadan et al. Expires November 19, 2018 [Page 27]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
NVE1
+------------+ DGW1
IP10+---+(BD-1) | +---------------+ +------------+
| \ | | | | |
|(IP-VRF)-(SBD)| |(SBD)-(IP-VRF)|-----+
| / IRB(IP1/M1) IRB(IP3/M3) | |
+---+(BD-2) | | | +------------+ _+_
| +------------+ | | ( )
SN1| | VXLAN/ | ( WAN )--H1
| NVE2 | GENEVE/ | (___)
| +------------+ | MPLS | DGW2 +
+---+(BD-2) | | | +------------+ |
| \ | | | | | |
|(IP-VRF)-(SBD)| |(SBD)-(IP-VRF)|-----+
| / IRB(IP2/M2) IRB(IP4/M4) |
SN2+----+(BD-3) | +---------------+ +------------+
+------------+
Figure 9 Interface-ful with SBD IRB model
In this model:
a) As in Section 4.4.1, the NVEs and DGWs must provide connectivity
between hosts in SN1, SN2, IP10 and hosts sitting at the other end
of the WAN.
b) However, the NVE/DGWs are now connected through Ethernet NVO
tunnels terminated in the SBD instance. The IP-VRFs use IRB
interfaces for their connectivity to the SBD.
c) Each SBD IRB has an IP and a MAC address, where the IP address
must be reachable from other NVEs or DGWs.
d) The SBD is attached to all the NVE/DGWs in the tenant domain BDs.
e) The solution must provide layer 3 connectivity for Ethernet NVO
tunnels, for instance, VXLAN or GENEVE (with Ethernet payload).
EVPN type 5 routes will be used to advertise the IP Prefixes, whereas
EVPN RT-2 routes will advertise the MAC/IP addresses of each SBD IRB
interface. Each NVE/DGW will advertise an RT-5 for each of its
prefixes with the following fields:
o RD as per [RFC7432].
o Ethernet Tag ID=0.
Rabadan et al. Expires November 19, 2018 [Page 28]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
o IP Prefix Length and IP address, as explained in the previous
Sections.
o GW IP address=IRB-IP of the SBD (this is the Overlay Index
that will be used for the recursive route resolution).
o ESI=0
o Label value should be zero since the RT-5 route requires a
recursive lookup resolution to an RT-2 route. It is ignored on
reception, and, when forwarding packets, the MPLS label or VNI
from the RT-2's MPLS Label1 field is used.
Each RT-5 will be sent with a Route Target identifying the tenant
(IP-VRF). The Router's MAC Extended Community should not be sent in
this case.
The following example illustrates the procedure to advertise and
forward packets to SN1/24 (IPv4 prefix advertised from NVE1):
(1) NVE1 advertises the following BGP routes:
o Route type 5 (IP Prefix route) containing:
. IPL=24, IP=SN1, Label= SHOULD be set to 0.
. GW IP=IP1 (SBD IRB's IP)
. Route Target identifying the tenant (IP-VRF).
o Route type 2 (MAC/IP route for the SBD IRB) containing:
. ML=48, M=M1, IPL=32, IP=IP1, Label=10.
. A [RFC5512] BGP Encapsulation Extended Community.
. Route Target identifying the SBD. This Route Target may be
the same as the one used with the RT-5.
(2) DGW1 imports the received routes from NVE1:
o DGW1 installs SN1/24 in the IP-VRF identified by the RT-5
Route Target.
. Since GW IP is different from zero, the GW IP (IP1) will be
used as the Overlay Index for the recursive route resolution
to the RT-2 carrying IP1.
Rabadan et al. Expires November 19, 2018 [Page 29]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
(3) When DGW1 receives a packet from the WAN with destination IPx,
where IPx belongs to SN1/24:
o A destination IP lookup is performed on the DGW1 IP-VRF
routing table. The lookup yields SN1/24, which is associated
to the Overlay Index IP1. The forwarding information is
derived from the RT-2 received for IP1.
o The IP packet destined to IPx is encapsulated with: Source
inner MAC = M3, Destination inner MAC = M1, Source outer IP
(source VTEP) = DGW1 IP, Destination outer IP (destination
VTEP) = IP1.
(4) When the packet arrives at NVE1:
o NVE1 will identify the IP-VRF for an IP lookup based on the
Label and the inner MAC DA.
o An IP lookup is performed in the routing context, where SN1
turns out to be a local subnet associated to BD-2. A
subsequent lookup in the ARP table and the BD FIB will provide
the forwarding information for the packet in BD-2.
The model described above is called 'Interface-ful with SBD IRB
model' because the tunnels connecting the DGWs and NVEs need to be
terminated into the SBD. The SBD is connected to the IP-VRFs via SBD
IRB interfaces, and that allows the recursive resolution of RT-5s to
GW IP addresses.
4.4.3 Interface-ful IP-VRF-to-IP-VRF with Unnumbered SBD IRB
Figure 10 will be used for the description of this model. Note that
this model is similar to the one described in Section 4.4.2, only
without IP addresses on the SBD IRB interfaces.
Rabadan et al. Expires November 19, 2018 [Page 30]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
NVE1
+------------+ DGW1
IP1+----+(BD-1) | +---------------+ +------------+
| \ | | | | |
|(IP-VRF)-(SBD)| (SBD)-(IP-VRF) |-----+
| / IRB(M1)| | IRB(M3) | |
+---+(BD-2) | | | +------------+ _+_
| +------------+ | | ( )
SN1| | VXLAN/ | ( WAN )--H1
| NVE2 | GENEVE/ | (___)
| +------------+ | MPLS | DGW2 +
+---+(BD-2) | | | +------------+ |
| \ | | | | | |
|(IP-VRF)-(SBD)| (SBD)-(IP-VRF) |-----+
| / IRB(M2)| | IRB(M4) |
SN2+----+(BD-3) | +---------------+ +------------+
+------------+
Figure 10 Interface-ful with unnumbered SBD IRB model
In this model:
a) As in Section 4.4.1 and 4.4.2, the NVEs and DGWs must provide
connectivity between hosts in SN1, SN2, IP1 and hosts sitting at
the other end of the WAN.
b) As in Section 4.4.2, the NVE/DGWs are connected through Ethernet
NVO tunnels terminated in the SBD instance. The IP-VRFs use IRB
interfaces for their connectivity to the SBD.
c) However, each SBD IRB has a MAC address only, and no IP address
(that is why the model refers to an 'unnumbered' SBD IRB). In this
model, there is no need to have IP reachability to the SBD IRB
interfaces themselves and there is a requirement to limit the
number of IP addresses used.
d) As in Section 4.4.2, the SBD is composed of all the NVE/DGW BDs of
the tenant that need inter-subnet-forwarding.
e) As in Section 4.4.2, the solution must provide layer 3
connectivity for Ethernet NVO tunnels, for instance, VXLAN or
GENEVE (with Ethernet payload).
This model will also make use of the RT-5 recursive resolution. EVPN
type 5 routes will advertise the IP Prefixes along with the Router's
MAC Extended Community used for the recursive lookup, whereas EVPN
RT-2 routes will advertise the MAC addresses of each SBD IRB
Rabadan et al. Expires November 19, 2018 [Page 31]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
interface (this time without an IP).
Each NVE/DGW will advertise an RT-5 for each of its prefixes with the
same fields as described in 4.4.2 except for:
o GW IP address= set to 0.
Each RT-5 will be sent with a Route Target identifying the tenant
(IP-VRF) and the Router's MAC Extended Community containing the MAC
address associated to SBD IRB interface. This MAC address may be
reused for all the IP-VRFs in the NVE.
The example is similar to the one in Section 4.4.2:
(1) NVE1 advertises the following BGP routes:
o Route type 5 (IP Prefix route) containing the same values as
in the example in Section 4.4.2, except for:
. GW IP= SHOULD be set to 0.
. Router's MAC Extended Community containing M1 (this will be
used for the recursive lookup to a RT-2).
o Route type 2 (MAC route for the SBD IRB) with the same values
as in Section 4.4.2 except for:
. ML=48, M=M1, IPL=0, Label=10.
(2) DGW1 imports the received routes from NVE1:
o DGW1 installs SN1/24 in the IP-VRF identified by the RT-5
Route Target.
. The MAC contained in the Router's MAC Extended Community
sent along with the RT-5 (M1) will be used as the Overlay
Index for the recursive route resolution to the RT-2
carrying M1.
(3) When DGW1 receives a packet from the WAN with destination IPx,
where IPx belongs to SN1/24:
o A destination IP lookup is performed on the DGW1 IP-VRF
routing table. The lookup yields SN1/24, which is associated
to the Overlay Index M1. The forwarding information is derived
from the RT-2 received for M1.
o The IP packet destined to IPx is encapsulated with: Source
Rabadan et al. Expires November 19, 2018 [Page 32]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
inner MAC = M3, Destination inner MAC = M1, Source outer IP
(source VTEP) = DGW1 IP, Destination outer IP (destination
VTEP) = NVE1 IP.
(4) When the packet arrives at NVE1:
o NVE1 will identify the IP-VRF for an IP lookup based on the
Label and the inner MAC DA.
o An IP lookup is performed in the routing context, where SN1
turns out to be a local subnet associated to BD-2. A
subsequent lookup in the ARP table and the BD FIB will provide
the forwarding information for the packet in BD-2.
The model described above is called Interface-ful with unnumbered SBD
IRB model (as in Section 4.4.2), only this time the SBD IRB does not
have an IP address.
5. Security Considerations
This document provides a set of procedures to achieve Inter-Subnet
Forwarding across NVEs or PEs attached to a group of BDs that belong
to the same tenant (or VPN). The security considerations discussed in
[RFC7432] apply to the Intra-Subnet Forwarding or communication
within each of those BDs. In addition, the security considerations in
[RFC4364] should also be understood, since this document and
[RFC4364] may be used in similar applications.
Contrary to [RFC4364], this document does not describe PE/CE route
distribution techniques, but rather considers the CEs as TSes or VAs
that do not run dynamic routing protocols. This can be considered a
security advantage, since dynamic routing protocols can be blocked on
the NVE/PE ACs, not allowing the tenant to interact with the
infrastructure's dynamic routing protocols.
In this document, the RT-5 may use a regular BGP Next Hop for its
resolution or an Overlay Index that requires a recursive resolution
to a different EVPN route (an RT-2 or an RT-1). In the latter case,
it is worth noting that any action that ends up filtering or
modifying the RT-2/RT-1 routes used to convey the Overlay Indexes,
will modify the resolution of the RT-5 and therefore the forwarding
of packets to the remote subnet.
6. IANA Considerations
This document requests value 5 in the [EVPNRouteTypes] registry
Rabadan et al. Expires November 19, 2018 [Page 33]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
defined by [RFC7432]:
Value Description Reference
5 IP Prefix route [this document]
7. References
7.1 Normative References
[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, <http://www.rfc-
editor.org/info/rfc7432>.
[RFC5512] Mohapatra, P. and E. Rosen, "The BGP Encapsulation
Subsequent Address Family Identifier (SAFI) and the BGP Tunnel
Encapsulation Attribute", RFC 5512, DOI 10.17487/RFC5512, April 2009,
<http://www.rfc-editor.org/info/rfc5512>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March
1997, <http://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC2119
Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017,
<http://www.rfc-editor.org/info/rfc8174>.
[RFC8365] Sajassi-Drake et al., "A Network Virtualization Overlay
Solution using EVPN", RFC 8365, DOI 10.17487/RFC8365, March, 2018.
[EVPN-INTERSUBNET] Sajassi et al., "IP Inter-Subnet Forwarding in
EVPN", draft-ietf-bess-evpn-inter-subnet-forwarding-03.txt, work in
progress, February, 2017
[EVPNRouteTypes] IANA EVPN Route Type registry,
https://www.iana.org/assignments/evpn
7.2 Informative References
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February 2006,
<http://www.rfc-editor.org/info/rfc4364>.
[RFC7606] Chen, E., Scudder, J., Mohapatra, P., and K. Patel,
"Revised Error Handling for BGP UPDATE Messages", RFC 7606, August
Rabadan et al. Expires November 19, 2018 [Page 34]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
2015, <http://www.rfc-editor.org/info/rfc7606>.
[802.1D-REV] "IEEE Standard for Local and metropolitan area networks
- Media Access Control (MAC) Bridges", IEEE Std. 802.1D, June 2004.
[802.1Q] "IEEE Standard for Local and metropolitan area networks -
Media Access Control (MAC) Bridges and Virtual Bridged Local Area
Networks", IEEE Std 802.1Q(tm), 2014 Edition, November 2014.
[RFC7365] Lasserre, M., Balus, F., Morin, T., Bitar, N., and Y.
Rekhter, "Framework for Data Center (DC) Network Virtualization", RFC
7365, DOI 10.17487/RFC7365, October 2014, <https://www.rfc-
editor.org/info/rfc7365>.
[RFC5227] Cheshire, S., "IPv4 Address Conflict Detection", RFC 5227,
DOI 10.17487/RFC5227, July 2008, <https://www.rfc-
editor.org/info/rfc5227>.
[RFC7348] Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger,
L., Sridhar, T., Bursell, M., and C. Wright, "Virtual eXtensible
Local Area Network (VXLAN): A Framework for Overlaying Virtualized
Layer 2 Networks over Layer 3 Networks", RFC 7348, DOI
10.17487/RFC7348, August 2014, <https://www.rfc-
editor.org/info/rfc7348>.
[GENEVE] Gross, J., Ed., Ganga, I., Ed., and T. Sridhar, Ed.,
"Geneve: Generic Network Virtualization Encapsulation", Work in
Progress, draft-ietf-nvo3-geneve-06, March 2018.
8. Acknowledgments
The authors would like to thank Mukul Katiyar and Jeffrey Zhang for
their valuable feedback and contributions. The following people also
helped improving this document with their feedback: Tony Przygienda
and Thomas Morin. Special THANK YOU to Eric Rosen for his detailed
review, it really helped improve the readability and clarify the
concepts. Thank you to Alvaro Retana for his thorough review.
9. Contributors
In addition to the authors listed on the front page, the following
co-authors have also contributed to this document:
Senthil Sathappan
Florin Balus
Aldrin Isaac
Senad Palislamovic
Rabadan et al. Expires November 19, 2018 [Page 35]
Internet-Draft EVPN Prefix Advertisement May 18, 2018
Samir Thoria
10. Authors' Addresses
Jorge Rabadan (Editor)
Nokia
777 E. Middlefield Road
Mountain View, CA 94043 USA
Email: jorge.rabadan@nokia.com
Wim Henderickx
Nokia
Email: wim.henderickx@nokia.com
John E. Drake
Juniper
Email: jdrake@juniper.net
Ali Sajassi
Cisco
Email: sajassi@cisco.com
Wen Lin
Juniper
Email: wlin@juniper.net
Rabadan et al. Expires November 19, 2018 [Page 36]
