Multipath for EVPN Ethernet Auto-Discovery Routes
draft-li-bess-evpn-ead-multipath-00
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Zhiqiang Li , Zongpeng Du , Junjie Wang , Wei Cheng , Guoying Zhang , Xun Sun , Chunhao Zhao | ||
| Last updated | 2026-07-04 | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
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| Send notices to | (None) |
draft-li-bess-evpn-ead-multipath-00
BESS Z. Li
Internet-Draft Z. Du
Intended status: Standards Track China Mobile
Expires: 5 January 2027 J. Wang
W. Cheng
G. Zhang
Centec
X. Sun
Inesa
C. Zhao
SAIA
4 July 2026
Multipath for EVPN Ethernet Auto-Discovery Routes
draft-li-bess-evpn-ead-multipath-00
Abstract
In EVPN multi-homing deployments, multiple PE devices attached to the
same Ethernet Segment each originate Ethernet Auto-Discovery (EAD)
routes. Standard BGP best-path selection retains only one route per
NLRI key, which can suppress reachability information needed for EVPN
aliasing, fast convergence, and split-horizon filtering.
This document specifies that BGP speakers MUST treat EAD routes as
multipath and MUST advertise and install all valid EAD routes for a
given Ethernet Segment, rather than selecting a single best path.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 5 January 2027.
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Copyright Notice
Copyright (c) 2026 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
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. EAD Route Multipath Requirements . . . . . . . . . . . . . . 3
2.1. Applicability . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Advertisement . . . . . . . . . . . . . . . . . . . . . . 3
2.3. Forwarding State Installation . . . . . . . . . . . . . . 4
3. Operational Considerations . . . . . . . . . . . . . . . . . 4
3.1. Route Distinguisher Allocation . . . . . . . . . . . . . 4
3.2. Interoperability . . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Normative References . . . . . . . . . . . . . . . . . . . . 5
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
BGP MPLS-Based Ethernet VPN (EVPN) [RFC7432] defines Ethernet Auto-
Discovery (EAD) routes (Route Type 1) for multi-homing functions
including fast convergence (Section 8.2), split-horizon filtering
(Section 8.3), and aliasing (Section 8.4). In a multi-homing
deployment, multiple Provider Edge (PE) devices attached to the same
Ethernet Segment (ES) each originate EAD routes that share the same
Ethernet Segment Identifier (ESI).
Per [RFC7432] Section 7.1, the BGP route key for an EAD route
comprises the Route Distinguisher (RD), the ESI, and the Ethernet Tag
ID. The originating PE's IP address is not part of the route key.
When multiple PEs originate EAD routes with the same RD and ESI,
standard BGP [RFC4271] best-path selection treats them as competing
paths for the same prefix and retains only one.
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While [RFC7432] recommends that each PE use a unique RD to
distinguish its routes, this recommendation is not always followed in
practice. Additionally, even with unique RDs, Route Reflector (RR)
topologies may reflect only a subset of paths to their clients. In
either case, retaining a single best path for EAD routes can result
in:
* Remote PEs not receiving EAD routes from all PEs attached to an
ES, preventing correct aliasing per [RFC7432] Section 8.4.
* Incomplete mass withdrawal, as the withdrawal of an EAD per-ES
route from one PE is not received by all remote PEs.
* Incomplete forwarding state for ES and EVI labels, affecting
split-horizon filtering for multi-homing groups with more than two
PEs.
This document specifies the multipath requirements for EAD routes to
address these issues.
1.1. 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.
2. EAD Route Multipath Requirements
2.1. Applicability
The requirements in this section apply to EVPN Route Type 1 (Ethernet
Auto-Discovery) routes with a non-zero ESI. Routes with ESI set to
zero and all other EVPN route types are subject to standard BGP best-
path selection per [RFC4271] Section 9.1.2 without modification.
2.2. Advertisement
A BGP speaker MUST advertise all valid EAD routes for a given ESI to
its BGP peers, regardless of the outcome of best-path selection.
This applies to both locally originated and received EAD routes.
This requirement applies to Route Reflectors, which MUST reflect all
valid EAD routes for a given ESI to their clients, rather than
reflecting only the best path.
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This behavior is functionally equivalent to BGP Add-Paths [RFC7911]
for the specific case of EAD routes, without requiring Add-Paths
capability negotiation.
2.3. Forwarding State Installation
A BGP speaker MUST install forwarding state for all valid EAD routes
for a given ESI, not only the best path. Specifically:
* For EAD per-ES routes, the ES label from each route originator
MUST be installed.
* For EAD per-EVI routes, the EVI label from each route originator
MUST be installed.
The resulting forwarding state maps the ESI and EVI to the set of
originating PE addresses and their associated labels.
3. Operational Considerations
3.1. Route Distinguisher Allocation
The multipath requirements in this document do not remove the
recommendation in [RFC7432] to assign unique RDs per PE. Unique RDs
remain useful for operational troubleshooting and route
identification. The requirements specified here apply regardless of
whether RDs are unique or shared.
3.2. Interoperability
A BGP speaker implementing this specification advertises additional
EAD routes that a non-implementing peer would not. The additional
routes are valid BGP UPDATE messages and are processed normally by
the receiving peer. A non-implementing peer may apply standard best-
path selection to these routes; this does not cause protocol errors,
but may result in the peer not utilizing all available paths.
4. Security Considerations
Treating EAD routes as multipath increases the number of routes in
the BGP Loc-RIB and the forwarding plane. A misconfigured or
malicious peer could originate a large number of EAD routes for the
same ESI. Implementations MUST support a configurable limit on the
number of paths accepted per ESI. When this limit is reached,
additional routes SHOULD be discarded.
BGP session authentication using TCP-AO [RFC5925] is RECOMMENDED to
protect against unauthorized route injection.
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5. IANA Considerations
This document has no IANA actions.
6. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, DOI 10.17487/RFC4271,
January 2006, <https://www.rfc-editor.org/info/rfc4271>.
[RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP
Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
June 2010, <https://www.rfc-editor.org/info/rfc5925>.
[RFC7432] Sajassi, A., 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>.
[RFC7911] Walton, D., Retana, A., Chen, E., and J. Scudder,
"Advertisement of Multiple Paths in BGP", RFC 7911,
DOI 10.17487/RFC7911, July 2016,
<https://www.rfc-editor.org/info/rfc7911>.
[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>.
Acknowledgements
The multi-homing procedures in RFC 7432 and the ongoing work on its
revision informed the requirements in this document.
Authors' Addresses
Zhiqiang Li
China Mobile
Beijing
100053
China
Email: lizhiqiangyjy@chinamobile.com
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Zongpeng Du
China Mobile
Beijing
100053
China
Email: duzongpeng@chinamobile.com
Junjie Wang
Centec
Shanghai
201203
China
Email: wangjj@centec.com
Wei Cheng
Centec
Shanghai
201203
China
Email: chengw@centec.com
Guoying Zhang
Centec
Shanghai
201203
China
Email: zhanggy@centec.com
Xun Sun
Inesa
Shanghai
200030
China
Email: sunxun@inesa.com
Chunhao Zhao
SAIA
Shanghai
200125
China
Email: chunhao.zhao@sh-aia.com
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