Internet DRAFT - draft-ietf-bess-evpn-vpws-fxc
draft-ietf-bess-evpn-vpws-fxc
BESS Working Group A. Sajassi, Ed.
Internet-Draft P. Brissette
Intended status: Standards Track Cisco Systems
Expires: 27 April 2023 J. Uttaro
AT&T
J. Drake
Juniper Networks
S. Boutros
Ciena
J. Rabadan
Nokia
24 October 2022
EVPN VPWS Flexible Cross-Connect Service
draft-ietf-bess-evpn-vpws-fxc-08
Abstract
This document describes a new EVPN VPWS service type specifically for
multiplexing multiple attachment circuits across different Ethernet
Segments and physical interfaces into a single EVPN VPWS service
tunnel and still providing Single-Active and All-Active multi-homing.
This new service is referred to as flexible cross-connect service.
After a description of the rationale for this new service type, the
solution to deliver such service is detailed.
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/.
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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 27 April 2023.
Copyright Notice
Copyright (c) 2022 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 (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 . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1. VPWS Service Identifiers . . . . . . . . . . . . . . . . 8
3.2. Default Flexible Xconnect . . . . . . . . . . . . . . . . 8
3.2.1. Multi-homing . . . . . . . . . . . . . . . . . . . . 9
3.3. VLAN-Signaled Flexible Xconnect . . . . . . . . . . . . . 9
3.3.1. Local Switching . . . . . . . . . . . . . . . . . . . 10
3.4. Service Instantiation . . . . . . . . . . . . . . . . . . 11
4. BGP Extensions . . . . . . . . . . . . . . . . . . . . . . . 11
5. Failure Scenarios . . . . . . . . . . . . . . . . . . . . . . 12
5.1. EVPN VPWS Service Failure . . . . . . . . . . . . . . . . 14
5.2. Attachment Circuit Failure . . . . . . . . . . . . . . . 14
5.3. PE Port Failure . . . . . . . . . . . . . . . . . . . . . 15
5.4. PE Node Failure . . . . . . . . . . . . . . . . . . . . . 15
6. Security Considerations . . . . . . . . . . . . . . . . . . . 15
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
8.1. Normative References . . . . . . . . . . . . . . . . . . 15
8.2. Informative References . . . . . . . . . . . . . . . . . 16
Appendix A. Contributors . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
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1. Introduction
[RFC8214] describes a solution to deliver P2P services using BGP
constructs defined in [RFC7432]. It delivers this P2P service
between a pair of Attachment Circuits (ACs), where an AC can
designate on a PE, a port, a VLAN on a port, or a group of VLANs on a
port. It also leverages multi-homing and fast convergence
capabilities of [RFC7432] in delivering these VPWS services.
Multi-homing capabilities include the support of single-active and
all-active redundancy mode and fast convergence is provided using
"mass withdrawal" message in control-plane and fast protection
switching using prefix independent convergence in data-plane upon
node or link failure [I-D.ietf-rtgwg-bgp-pic]. Furthermore, the use
of EVPN BGP constructs eliminates the need for multi-segment PW
auto-discovery and signaling if the VPWS service need to span across
multiple ASes.
Some service providers have very large number of ACs (in millions)
that need to be back hauled across their MPLS/IP network. These ACs
may or may not require tag manipulation (e.g., VLAN translation).
These service providers want to multiplex a large number of ACs
across several physical interfaces spread across one or more PEs
(e.g., several Ethernet Segments) onto a single VPWS service tunnel
in order to a) reduce number of EVPN service labels associated with
EVPN-VPWS service tunnels and thus the associated OAM monitoring, and
b) reduce EVPN BGP signaling (e.g., not to signal each AC as it is
the case in [RFC8214]).
These service provider want the above functionality without
scarifying any of the capabilities of [RFC8214] including single-
active and all-active multi-homing, and fast convergence.
This document presents a solution based on extensions to [RFC8214] to
meet the above requirements.
1.1. Terminology
AC: Attachment Circuit
A-D: Auto Discovery
CE: Customer Edge device e.g., host or router or switch
EPL: Ethernet Private Line
ES: Ethernet Segment
ESI: Ethernet Segment Identififer
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EVI: EVPN Instance Identifier
EVPL: Ethernet Virtual Private Line
EVPN: Ethernet Virtual Private Network
FXC: Flexible Cross Connect
L2: Layer 2
MAC: Media Access Control
MPLS: Multi Protocol Label Switching
MTU: Maximum Transmit Unit
OAM: Operations, Administration and Maintenance
PE: Provider Edge device
PW: Pseudowire
RT: Route Target
VCCV: Virtual circuit connection verification
VID: Vlan ID
VPWS: Virtual private wire service
VRF: Virtual Route Forwarding
VPWS Service Tunnel: It is represented by a pair of EVPN service
labels associated with a pair of endpoints. Each label is
downstream assigned and advertised by the disposition PE through
an Ethernet A-D per-EVI route. The downstream label identifies
the endpoint on the disposition PE. A VPWS service tunnel can be
associated with many VPWS service identifiers where each
identifier is a normalized VID.
Single-Active Redundancy Mode: When a device or a network is
multi-homed to two or more PEs and when only a single PE in such
redundancy group can forward traffic to/from the multi-homed
device or network for a given VLAN, then such multi-homing or
redundancy is referred to as "Single-Active".
All-Active Redundancy Mode: When a device is multi-homed to two or
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more PEs and when all PEs in such redundancy group can forward
traffic to/from the multi-homed device for a given VLAN, then such
multi-homing or redundancy is referred to as "All-Active".
2. Requirements
Two of the main motivations for service providers seeking a new
solution are: 1) to reduce number of VPWS service tunnels by
multiplexing large number of ACs across different physical interfaces
instead of having one VPWS service tunnel per AC, and 2) to reduce
the signaling of ACs as much as possible. Besides these two
requirements, they also want multi-homing and fast convergence
capabilities of [RFC8214].
In [RFC8214], a PE signals an AC indirectly by first associating that
AC to a VPWS service tunnel (e.g., a VPWS service instance) and then
signaling the VPWS service tunnel via a Ethernet A-D per EVI route
with Ethernet Tag field set to a 24-bit VPWS service instance
identifier (which is unique within the EVI) and ESI field set to a
10-octet identifier of the Ethernet Segment corresponding to that AC.
Therefore, a PE device that receives such EVPN routes, can associate
the VPWS service tunnel to the remote Ethernet Segment, and when the
remote ES fails and the PE receives the "mass withdrawal" message
associated with the failed ES per [RFC7432], it can update its BGP
path list for that VPWS service tunnel quickly and achieve fast
convergence for multi-homing scenarios. Even if fast convergence
were not needed, there would still be a need for signaling each AC
failure (via its corresponding VPWS service tunnel) associated with
the failed ES, so that the BGP path list for each of them gets
updated accordingly and the packets are sent to backup PE (in case of
single- active multi-homing) or to other PEs in the redundancy group
(in case of all-active multi-homing). In absence of updating the BGP
path list, the traffic for that VPWS service tunnel will be
black-holed.
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When a single VPWS service tunnel multiplexes many ACs across number
of Ethernet Segments (number of physical interfaces) and the ACs are
not signaled via EVPN BGP to remote PE devices, then the remote PE
devices neither know the association of the received Ethernet Segment
to these ACs (and in turn to their local ACs) nor they know the
association of the VPWS service tunnel (e.g., EVPN service label) to
the far-end ACs - i.e, the remote PEs only know the association of
their local ACs to the VPWS service tunnel but not the far-end ACs.
Thus upon a connectivity failure to the ES, they don't know how to
redirect traffic via another multi-homing PE to that ES. In other
words, even if an ES failure is signaled via EVPN to the remote PE
devices, they don't know what to do with such message because they
don't know the association among the remote ES, the remote ACs, and
the VPWS service tunnel.
In order to address this issue when multiplexing large number of ACs
onto a single VPWS service tunnel, two mechanisms are devised: one to
support VPWS services between two single-homed endpoints and another
one to support VPWS services where one of the endpoints is multi-
homed.
For single-homed endpoints, it is OK not to signal each AC in BGP
because upon connection failure to the ES, there is no alternative
path to that endpoint. However, the ramification for not signaling
an AC failure is that the traffic destined to the failed AC, is sent
over MPLS/IP core and then gets discarded at the destination PE -
i.e., it can waste network resources.
This waste of network resources upon connection failure may be
transient as it is detectable and preventable at the application
layer in some cases. Section 3.2 describes a solution for such
single-homing VPWS service.
For VPWS services where one of the endpoints is multi-homed, there
are two options:
1) to signal each AC via BGP so that the path list can be updated
upon a failure that impacts those ACs. This solution is described in
Section 3.3 and it is called VLAN-signaled flexible cross-connect
service.
2) to bundle several ACs on an ES together per destination end-point
(e.g., ES, MAC-VRF, etc.) and associate such bundle to a single VPWS
service tunnel. This is similar to VLAN-bundle service interface
described in [RFC8214]. This solution is described in Section 3.2.1.
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3. Solution
This section describes a solution for providing a new VPWS service
between two PE devices where a large number of ACs (e.g., VLANs) that
span across many Ethernet Segments (i.e., physical interfaces) on
each PE are multiplex onto a single P2P EVPN service tunnel. Since
multiplexing is done across several physical interfaces, there can be
overlapping VLAN IDs across these interfaces; therefore, in such
scenarios, the VLAN IDs (VIDs) MUST be translated into unique VIDs to
avoid collision. Furthermore, if the number of VLANs that are
getting multiplex onto a single VPWS service tunnel exceed 4095, then
a single tag to double tag translation MUST be performed. This
translation of VIDs into unique VIDs (either single or double) is
referred to as "VID normalization".
When single normalized VID is used, the lower 12-bit of Ethernet tag
field in EVPN routes MUST be set to that VID and when double
normalized VID is used, the lower 12-bit of Ethernet tag field MUST
be set to inner VID and the higher 12-bit is set to the outer VID.
As in [RFC8214], 12-bit and 24-bit VPWS service instance identifiers
representing normalised VIDs MUST be right-aligned.
Since there is only a single EVPN VPWS service tunnel associated with
many normalized VIDs (either single or double) across multiple
physical interfaces, MPLS lookup at the disposition PE is no longer
sufficient to forward the packet to the right egress
endpoint/interface. Therefore, in addition to an EVPN label lookup
corresponding to the VPWS service tunnel, a VID lookup (either single
or double) is also required. On the disposition PE, one can think of
the lookup of EVPN label results in identification of a VID-VRF, and
the lookup of normalized VID(s) in that table, results in
identification of egress endpoint/interface. The tag manipulation
(translation from normalized VID(s) to local VID) SHOULD be performed
either as part of the VID table lookup or at the egress interface
itself.
Since VID lookup (single or double) needs to be performed at the
disposition PE, then VID normalization MUST be performed prior to the
MPLS encapsulation on the ingress PE. This requires that both
imposition and disposition PE devices be capable of VLAN tag
manipulation, such as re-write (single or double), addition, deletion
(single or double) at their endpoints (e.g., their ES's, MAC-VRFs,
IP-VRFs, etc.). Operators should be informed of possible trade-offs
from performance standpoint, compared to usual PW processing.
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3.1. VPWS Service Identifiers
In [RFC8214], a unique value in the context of each PE's EVI is
signaled. The 32-bit Ethernet Tag ID field MUST be set to this VPWS
service instance identifier value.
For FXC, Ethernet Tag ID field value may represent:
* VLAN-Bundle : a unique value for a group of VLANs ;
* VLAN-Aware Bundle : a unique value for individual VLANs, and may
be considered same as the normalised VID
Both the VPWS service instance identifier and normalised VID are
carried in the Ethernet Tag ID field of the Ethernet A-D per EVI
route. For FXC, in the case of a 12-bit ID the VPWS service instance
identifier is the same as the single-tag normalised VID and will be
the same on both PEs. Similarly in the case of a 24-bit ID, the VPWS
service instance identifier is the same as the double-tag normalised
VID.
3.2. Default Flexible Xconnect
In this mode of operation, many ACs across several Ethernet Segments
are multiplex into a single EVPN VPWS service tunnel represented by a
single VPWS service ID. This is the default mode of operation for
FXC and the participating PEs do not need to signal the VLANs
(normalized VIDs) in EVPN BGP.
With respect to the data-plane aspects of the solution, both
imposition and disposition PEs MUST be aware of the VLANs as the
imposition PE performs VID normalization and the disposition PE does
VID lookup and translation. In this solution, there SHOULD only be a
single P2P EVPN VPWS service tunnel between a pair of PEs for a set
of ACs.
As discussed previously, since the EVPN VPWS service tunnel is used
to multiplex ACs across different ES's (e.g., physical interfaces),
the EVPN label alone is not sufficient for proper forwarding of the
received packets (over MPLS/IP network) to egress interfaces.
Therefore, normalized VID lookup is REQUIRED in the disposition
direction to forward packets to their proper egress end-points -
i.e., the EVPN label lookup identifies a VID-VRF and subsequently,
the normalized VID lookup in that table, identifies the egress
interface.
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In this solution, on each PE, the single-homing ACs represented by
their normalized VIDs are associated with a single EVPN VPWS service
tunnel (in a given EVI). The EVPN route that gets generated is an
Ethernet A-D per EVI route with ESI=0, Ethernet Tag field set to VPWS
service instance ID, MPLS label field set to dynamically generated
EVPN service label representing the EVPN VPWS service tunnel. This
route is sent with a Route Target (RT) representing the EVI. This RT
can be auto-generated from the EVI per Section 5.1.2.1 of [RFC8365].
Furthermore, this route is sent with the EVPN Layer-2 Extended
Community defined in Section 3.1 of [RFC8214] with two new flags
(defined in Section 4) that indicate: 1) this VPWS service tunnel is
for default Flexible Cross-Connect, and 2) normalized VID type
(single versus double). The receiving PE uses these new flags for
consistency check and MAY generate an alarm if it detects
inconsistency but doesn't bring down the VPWS service.
It should be noted that in this mode of operation, a single
Ethernet A-D per EVI route is sent upon configuration of the first AC
(ie, normalized VID). Later, when additional ACs are configured and
associated with this EVPN VPWS service tunnel, the PE does not
advertise any additional EVPN BGP routes. The PE only associates
locally these ACs with the already created VPWS service tunnel.
3.2.1. Multi-homing
The default FXC mode can also be used for multi-homing. In this
mode, a group of normalized VIDs (ACs) on a single Ethernet segment
that are destined to a single endpoint are multiplexed into a single
EVPN VPWS service tunnel represented by a single VPWS service ID.
When the default FXC mode is used for multi-homing, instead of a
single EVPN VPWS service tunnel, there can be many service tunnels
per pair of PEs - i.e, there is one tunnel per group of VIDs per pair
of PEs and there can be many groups between a pair of PEs, thus
resulting in many EVPN service tunnels.
3.3. VLAN-Signaled Flexible Xconnect
In this mode of operation, just as the default FXC mode in
Section 3.2, many normalized VIDs (ACs) across several different
ES's/interfaces are multiplexed into a single EVPN VPWS service
tunnel; however, this single tunnel is represented by many VPWS
service IDs (one per normalized VID) and these normalized VIDs are
signaled using EVPN BGP.
In this solution, on each PE, the multi-homing ACs represented by
their normalized VIDs are configured with a single EVI. There is no
need to configure VPWS service instance ID in here as it is the same
as the normalized VID. For each normalized VID on each ES, the PE
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generates an Ethernet A-D per EVI route where ESI field represents
the ES ID, the Ethernet Tag field is set to the normalized VID, MPLS
label field is set to dynamically generated EVPN label representing
the P2P EVPN service tunnel and it is the same label for all the ACs
that are multiplexed into a single EVPN VPWS service tunnel. This
route is sent with a Route Target (RT) representing the EVI. As
before, this RT can be auto-generated from the EVI per section
Section 5.1.2.1 of [RFC8365]. Furthermore, this route is sent with
the EVPN Layer-2 Extended Community defined in Section 3.1 of
[RFC8214] with two new flags (defined in Section 4) that indicate: 1)
this VPWS service tunnel is for VLAN-signaled Flexible Cross-Connect,
and 2) normalized VID type (single versus double). The receiving PE
uses these new flags for consistency check and MAY generate an alarm
if it detects inconsistency but doesn't bring down the VPWS service.
It should be noted that in this mode of operation, the PE sends a
single Ethernet A-D per EVI route for each AC that is configured -
i.e., each normalized VID that is configured per ES results in
generation of an EVPN Ethernet A-D per EVI.
This mode of operation provides automatic cross checking of
normalized VIDs used for EVPL services because these VIDs are
signaled in EVPN BGP. For example, if the same normalized VID is
configured on three PE devices (instead of two) for the same EVI,
then when a PE receives the second Ethernet A-D per EVI route, it
generates an error message unless the two Ethernet A-D per EVI routes
include the same ESI. Such cross-checking is not feasible in default
FXC mode because the normalized VIDs are not signaled.
3.3.1. Local Switching
When cross-connection is between two ACs belonging to two multi-homed
Ethernet Segments on the same set of multi-homing PEs, then
forwarding between the two ACs MUST be performed locally during
normal operation (e.g., in absence of a local link failure) - i.e.,
the traffic between the two ACs MUST be locally switched within the
PE.
In terms of control plane processing, this means that when the
receiving PE receives an Ethernet A-D per-EVI route whose ESI is a
local ESI, the PE does not alter its forwarding state based on the
received route. This ensures that the local switching takes
precedence over forwarding via MPLS/IP network. This scheme of
locally switched preference is consistent with baseline EVPN
[RFC7432] where it describes the locally switched preference for
MAC/IP routes.
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In such scenarios, the Ethernet A-D per EVI route should be
advertised with the MPLS label either associated with the destination
Attachment Circuit or with the destination Ethernet Segment in order
to avoid any ambiguity in forwarding. In other words, the MPLS label
cannot represent the same VID-VRF used in Section 3.3 because the
same normalized VID can be reachable via two Ethernet Segments. In
case of using MPLS label per destination AC, then this same solution
can be used for VLAN-based VPWS or VLAN-bundle VPWS services per
[RFC8214].
3.4. Service Instantiation
The V field defined in Section 4 is OPTIONAL. However, when
transmitted, its value could be flagging an error condition which may
result in an operational issue. Notification to operator of an error
is not sufficient, the VPWS service tunnel must not be established.
If both PEs of a VPWS tunnel are signaling a matching Normalised VID
in control plane, yet one is operating in single tag and the other in
double tag mode, the signaling of V-bit allows for detecting and
preventing this tunnel instantiation.
If single VID normalization is signaled in the Ethernet Tag ID field
(12-bits) yet dataplane is operating based double tags, the VID
normalization applies only to outer tag. If double VID normalization
is signaled in the Ethernet Tag ID field (24-bits), VID normalization
applies to both inner and outer tags.
4. BGP Extensions
This draft uses the EVPN Layer-2 attribute extended community defined
in [RFC8214] with two additional flags added to this EC as described
below. This EC is sent with Ethernet A-D per EVI route per
Section 3, and SHOULD be sent for Single-Active and All-Active
redundancy modes.
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+-------------------------------------------+
| Type (0x06) / Sub-type (0x04) (2 octets) |
+-------------------------------------------+
| Control Flags (2 octets) |
+-------------------------------------------+
| L2 MTU (2 octets) |
+-------------------------------------------+
| Reserved (2 octets) |
+-------------------------------------------+
1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ | V | M |-|C|P|B| (MBZ = MUST Be Zero)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The following bits in the Control Flags are defined; the remaining
bits MUST be set to zero when sending and MUST be ignored when
receiving this community.
Name Meaning
---------------------------------------------------------------
B,P,C per definition in [RFC8214]
- reserved for Flow-label
M 00 mode of operation as defined in [RFC8214]
01 VLAN-Signaled FXC
10 Default FXC
V 00 operating per [RFC8214]
01 single-VID normalization
10 double-VID normalization
The M and V fields are OPTIONAL. The M field is ignored at reception
for forwarding purposes and is used for error notifications.
5. Failure Scenarios
Two examples will be used as an example to analyze the failure
scenarios.
The first scenario is a default Flexible Xconnect with Multi- Homing
solution and it is depicted in Figure 1. In this case, the same VID
Normalization as in the previous example is performed, however there
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is not an individual Ethernet A-D per EVI route per normalized VID,
but per bundle of ACs on an ES. That is, PE1 will advertise two
Ethernet A-D per EVI routes: the first one will identify the ACs on
p1's ES and the second one will identify the AC2 in p2's ES.
Similarly, PE2 will advertise two Ethernet A-D per EVI routes.
N.VID 1,2,3 +---------------------+
PE1 | |
+---------+ IP/MPLS |
+-----+ VID1 p1 | +-----+ | sv.T1 +
| CE1 |-------------| FXC |======+ PE3 +-----+
| | /\ | | | | \ +----------+ +--| CE3 |
+-----+\ +||---| | sv.T2 \ | | 1/ | |
VID3\ / ||---| |=====+ \ | +-----+ | / +-----+
\ // \/ | +-----+ | \ +====| FXC |----+
\ / p2 +---------+ +======| | | 2 +-----+
/\ | | |----------| CE4 |
/ /\ +---------+ +=====| | | | |
/ / \p3 | +-----+ sv.T3 / +====| | | +-----+
VIDs1,2 / +----| FXC |=======+ / | | |---+
+-----+ / /\ | | | | / | +-----+ |\3 +-----+
| CE2 |-----||---| | | sv.T4 / | | \ | CE5 |
| |-----||---| | |======+ +----------+ +---| |
+--VIDs3,4 \/ | +-----+ | | +-----+
p4 +---------+ |
PE2 | |
N.VID 1,2,3 +-------------------+
Figure 1: Default Flexible Xconnect
The second scenario is depicted in Figure 2 and shows the
VLAN-signaled FXC mode with Multi-Homing. In this example:
* CE1 is connected to PE1 and PE2 via (port,vid)=(p1,1) and (p3,3)
respectively. CE1's VIDs are normalized to value 1 on both PEs,
and CE1 is Xconnected to CE3's VID 1 at the remote end.
* CE2 is connected to PE1 and PE2 via ports p2 and p4 respectively:
- (p2,1) and (p4,3) identify the ACs that are used to Xconnect
CE2 to CE4's VID 2, and are normalized to value 2.
- (p2,2) and (p4,4) identify the ACs that are used to Xconnect
CE2 to CE5's VID 3, and are normalized to value 3.
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In this scenario, PE1 and PE2 advertise an Ethernet A-D per EVI route
per normalized VID (values 1, 2 and 3), however only two VPWS Service
Tunnels are needed: VPWS Service Tunnel 1 (sv.T1) between PE1's FXC
service and PE3's FXC, and VPWS Service Tunnel 2 (sv.T2) between
PE2's FXC and PE3's FXC.
N.VID 1,2,3 +---------------------+
PE1 | |
+---------+ IP/MPLS |
+-----+ VID1 p1 | +-----+ | +
| CE1 |------------| FXC | | sv.T1 PE3 +-----+
| | /\ | | |=======+ +----------+ +--| CE3 |
+-----+\ +||---| | | \ | | 1/ | |
VID3\ / ||---| | | \ | +-----+ | / +-----+
\ / /\/ | +-----+ | +=====| FXC |----+
\ / p2 +---------+ | | | | 2 +-----+
/\ | | |----------| CE4 |
/ /\ +---------+ +======| | | | |
/ / \p3 | +-----+ | / | | | | +-----+
VIDs1,2 / +----| FXC | / | | |---+
+-----+ / /\ | | |======+ | +-----+ |\3 +-----+
| CE2 |-----||-----| | | sv.T2 | | \ | CE5 |
| |-----||-----| | | +----------+ +---| |
+-----+ \/ | +-----+ | | +-----+
VIDs3,4 p4 +---------+ |
PE2 | |
N.VID 1,2,3 +------------------+
Figure 2: VLAN-Signaled Flexible Xconnect
5.1. EVPN VPWS Service Failure
The failure detection of an EVPN VPWS service can be performed via
OAM mechanisms such as VCCV-BFD and upon such failure detection, the
switch over procedure to the backup S-PE is the same as the one
described above.
5.2. Attachment Circuit Failure
In case of AC Failure, the VLAN-Signaled and default FXC modes behave
in a different way:
* Default FXC (Figure 1): a VLAN or AC failure is not signaled in
the default mode, therefore in case of an AC failure, e.g. VID1
on CE2, nothing prevents PE3 from sending CE4's traffic to PE1,
creating a black-hole. Application layer OAM may be used if per-
VLAN fault propagation is required in this case.
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* VLAN-signaled FXC (Figure 2): a VLAN or AC failure, e.g. VID1 on
CE2, triggers the withdrawal of the Ethernet A-D per EVI route for
the corresponding Normalized VID, that is, Ethernet-Tag 2. When
PE3 receives the route withdrawal, it will remove PE1 from its
path-list for traffic coming from CE4.
5.3. PE Port Failure
In case of PE port Failure, the failure will be signaled and the
other PE will take over in both cases:
* Default FXC (Figure 1): a port failure, e.g. p2, is signaled by
route for sv.T2 will also be withdrawn. Upon receiving the fault
notification, PE3 will remove PE1 from its path-list for traffic
coming from CE4 and CE5.
* VLAN-signaled FXC (Figure 2): a port failure, e.g. p2, triggers
the withdrawal of the Ethernet A-D per EVI routes for Normalized
VIDs 2 and 3, as well as the withdrawal of the Ethernet A-D per ES
route for p2's ES. Upon receiving the fault notification, PE3
will withdraw PE1 from its path-list for the traffic coming from
CE4 and CE5.
5.4. PE Node Failure
In the case of PE node failure, the operation is similar to the steps
described above, albeit that EVPN route withdrawals are performed by
the Route Reflector instead of the PE.
6. Security Considerations
Since this document describes a muxing capability which leverages
EVPN-VPWS signaling, no additional functionality beyond the muxing
service is added and thus no additional security considerations are
needed beyond what is already specified in [RFC8214].
7. IANA Considerations
This document requests allocation of bits 4-7 in the "EVPN Layer 2
Attributes Control Flags" registry with names M and V:
M Signaling mode of operation (2 bits)
V VLAN-ID normalization (2 bits)
8. References
8.1. Normative References
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[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>.
[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>.
[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>.
8.2. Informative References
[I-D.ietf-rtgwg-bgp-pic]
Bashandy, A., Filsfils, C., and P. Mohapatra, "BGP Prefix
Independent Convergence", Work in Progress, Internet-
Draft, draft-ietf-rtgwg-bgp-pic-18, 9 April 2022,
<https://www.ietf.org/archive/id/draft-ietf-rtgwg-bgp-pic-
18.txt>.
[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>.
Appendix A. Contributors
In addition to the authors listed on the front page, the following
co-authors have also contributed substantially to this document:
Wen Lin
Juniper Networks
EMail: wlin@juniper.net
Luc Andre Burdet
Cisco
EMail: lburdet@cisco.com
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Authors' Addresses
Ali Sajassi (editor)
Cisco Systems
Email: sajassi@cisco.com
Patrice Brissette
Cisco Systems
Email: pbrisset@cisco.com
James Uttaro
AT&T
Email: uttaro@att.com
John Drake
Juniper Networks
Email: jdrake@juniper.net
Sami Boutros
Ciena
Email: sboutros@ciena.com
Jorge Rabadan
Nokia
Email: jorge.rabadan@nokia.com
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