wdiff rfc9721.original rfc9721.txt

BESS WorkGroup

Internet Engineering Task Force (IETF) N. Malhotra, Ed.
Internet-Draft
Request for Comments: 9721 A. Sajassi
Intended status:
Category: Standards Track A. Pattekar
Expires: 7 June 2025
ISSN: 2070-1721 Cisco Systems
J. Rabadan
Nokia
A. Lingala
AT&T
J. Drake
Juniper Networks
4 December 2024
April 2025

Extended Mobility Procedures for EVPN-IRB
draft-ietf-bess-evpn-irb-extended-mobility-21 Ethernet VPN Integrated Routing and
Bridging (EVPN-IRB)

Abstract

This document specifies extensions to the Ethernet VPN (EVPN) Integrated
Routing and Bridging (IRB) (EVPN-IRB) procedures specified in RFC7432 RFCs 7432 and
RFC9135
9135 to enhance the mobility mechanisms for EVPN-IRB networks based
networks. on EVPN-
IRB. The proposed extensions improve the handling of host mobility
and duplicate address detection in EVPN-IRB networks to cover a
broader set of scenarios where a host's unicast IP address to
MAC Media
Access Control (MAC) address bindings may change across moves. These
enhancements address limitations in the existing EVPN-IRB mobility
procedures by providing more efficient and scalable solutions. The
extensions are backward compatible with existing EVPN-IRB
implementations and aim to optimize network performance in scenarios
involving frequent IP address mobility.

NOTE TO IESG (TO BE DELETED BEFORE PUBLISHING): This draft lists six
authors which is above the required limit of five. Given significant
and active contributions to the draft from all six authors over the
course of six years, we would like to request IESG to allow
publication with six authors. Specifically, the three Cisco authors
are the original inventors of these procedures and contributed
heavily to rev 0 draft, most of which is still intact. AT&T is also
a key contributor towards defining the use cases that this document
addresses as well as the proposed solution. Authors from Nokia and
Juniper have further contributed to revisions and discussions
steadily over last six years to enable respective implementations and
a wider adoption.

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 an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list It represents the consensus of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for a maximum publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of six months this document, any errata,
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material or to cite them other than as "work in progress."

This Internet-Draft will expire on 7 June 2025.
https://www.rfc-editor.org/info/rfc9721.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Document Structure . . . . . . . . . . . . . . . . . . . 5
2. Requirements Language and Terminology . . . . . . . . . . . . 5
3. Background and Problem Statement . . . . . . . . . . . . . . 7
3.1. Optional MAC only MAC-Only RT-2 . . . . . . . . . . . . . . . . . 7
3.2. Mobility Use Cases . . . . . . . . . . . . . . . . . . . 7
3.2.1. Host MAC+IP Address Move . . . . . . . . . . . . . . 8
3.2.2. Host IP address Address Move to new New MAC address . . . . . . . 8 Address
3.2.2.1. Host Reload . . . . . . . . . . . . . . . . . . . 8
3.2.2.2. MAC Address Sharing . . . . . . . . . . . . . . . 8
3.2.2.3. Problem . . . . . . . . . . . . . . . . . . . . . 8
3.2.3. Host MAC address move Address Move to new New IP address . . . . . . . 9 Address
3.2.3.1. Problem . . . . . . . . . . . . . . . . . . . . . 10
3.3. EVPN All Active multi-homed Multi-Homed ES . . . . . . . . . . . . . 11
4. Design Considerations . . . . . . . . . . . . . . . . . . . . 12
5. Solution Components . . . . . . . . . . . . . . . . . . . . . 13
5.1. Sequence Number Inheritance . . . . . . . . . . . . . . . 13
5.2. MAC Address Sharing . . . . . . . . . . . . . . . . . . . 14
5.3. Sequence Number Synchronization . . . . . . . . . . . . . 15
6. Methods for Sequence Number Assignment . . . . . . . . . . . 16
6.1. Local MAC-IP learning . . . . . . . . . . . . . . . . . . 16 Learning
6.2. Local MAC learning . . . . . . . . . . . . . . . . . . . 16 Learning
6.3. Remote MAC or MAC-IP Route Update . . . . . . . . . . . . 17
6.4. Peer-Sync-Local MAC route update . . . . . . . . . . . . 17 Route Update
6.5. Peer-Sync-Local MAC-IP route update . . . . . . . . . . . 18 Route Update
6.6. Interoperability . . . . . . . . . . . . . . . . . . . . 18
6.7. MAC Address Sharing Race Condition . . . . . . . . . . . 19
6.8. Mobility Convergence . . . . . . . . . . . . . . . . . . 19
6.8.1. Generalized Probing Logic . . . . . . . . . . . . . . 20
7. Routed Overlay . . . . . . . . . . . . . . . . . . . . . . . 20
8. Duplicate Host Detection . . . . . . . . . . . . . . . . . . 21
8.1. Scenario A . . . . . . . . . . . . . . . . . . . . . . . 22
8.2. Scenario B . . . . . . . . . . . . . . . . . . . . . . . 22
8.2.1. Duplicate IP Detection Procedure for Scenario B . . . 23
8.3. Scenario C . . . . . . . . . . . . . . . . . . . . . . . 23
8.4. Duplicate Host Recovery . . . . . . . . . . . . . . . . . 24
8.4.1. Route Un-freezing Unfreezing Configuration . . . . . . . . . . . 24
8.4.2. Route Clearing Configuration . . . . . . . . . . . . 25
9. Security Considerations . . . . . . . . . . . . . . . . . . . 25
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 25
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 26
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 26
13.1.
11.1. Normative References . . . . . . . . . . . . . . . . . . 26
13.2.
11.2. Informative References . . . . . . . . . . . . . . . . . 27
Acknowledgements
Contributors
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27

1. Introduction

EVPN-IRB facilitates the advertisement of both MAC and IP routes via
a single MAC+IP Route Type 2 (RT-2) advertisement. The MAC address
is integrated into the local MAC-VRF MAC Virtual Routing and Forwarding (MAC-
VRF) bridge table, enabling Layer 2 (L2) bridged traffic across the
network overlay. The IP address is incorporated into the local ARP/NDP
Address Resolution Protocol (ARP) / Neighbor Discovery Protocol (NDP)
table in an asymmetric IRB
design, design or into the IP-VRF IP Virtual Routing and
Forwarding (IP-VRF) routing table in a symmetric IRB design,
facilitating design. This
facilitates routed traffic across the network overlay. For
additional context on EVPN-IRB forwarding modes, refer to [RFC9135].

To support the EVPN mobility procedure, a single sequence number
mobility attribute is advertised with the combined MAC+IP route.
This approach, which resolves both MAC and IP reachability with a
single sequence number, inherently assumes a fixed 1:1 mapping
between an IP address and MAC address. While this fixed 1:1 mapping
is a common use case and is addressed via the existing mobility
procedure defined in [RFC7432], there are additional IRB scenarios
that do not adhere to this assumption. Such scenarios are prevalent
in virtualized host environments where hosts connected to an EVPN
network are virtual machines Virtual Machines (VMs) or containerized workloads. The
following IRB mobility scenarios are considered:

* A host move results in the host's IP address and MAC address
moving together.

* A host move results in the host's IP address moving to a new MAC
address association.

* A host move results in the host's MAC address moving to a new IP
address association.

While the existing mobility procedure can manage the MAC+IP address
move in the first scenario, the subsequent scenarios lead to new MAC-
IP address associations. Therefore, a single sequence number
assigned independently per-{MAC for each {MAC address, IP address} is
insufficient to determine the most recent reachability for both MAC
address and IP
address address, unless the sequence number assignment
algorithm allows for changing MAC-IP address bindings across moves.

This document updates the sequence number assignment procedures
defined in [RFC7432] to adequately address mobility support across
EVPN-IRB overlay use cases that permit MAC-IP address bindings to
change across host moves and support mobility for both MAC and IP
route components carried in an EVPN RT-2 for these use cases.

Additionally, for hosts on an ESI Ethernet Segment Identifier (ESI) that
is multi-homed to multiple PE Provider Edge (PE) devices, additional
procedures are specified to ensure synchronized sequence number
assignments across the multi-homing devices.

This document addresses mobility for the following cases, independent
of the overlay encapsulation (e.g., MPLS, SRv6, NVO Tunnel): Segment Routing over IPv6
(SRv6), and Network Virtualization Overlay (NVO) tunnel):

* Symmetric EVPN-IRB overlay

* Asymmetric EVPN-IRB overlay

* Routed EVPN overlay

1.1. Document Structure

Following

The following sections of the document are informative:

* section Section 3 provides the necessary background and problem statement
being addressed in this document.

* section Section 4 lists the resulting design considerations for the
document.

* section Section 5 lists the main solution components that are foundational
for the sepecifications specifications that follow in subsequent sections.

Following

The following sections of the document are normative:

* section Section 6 describes the mobility and sequence number assigment assignment
procedures in an EVPN-IRB overlay that are required to address the
scenarios described in section Section 4.

* section Section 7 describes the mobility procedures for a routed overlay
network as opposed to an IRB overlay.

* section Section 8 describes corresponding duplicate detection procedures
for EVPN-IRB and routed overlays.

2. Requirements Language and 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.

EVPN-IRB: Ethernet VPN Integrated Routing and Bridging. A BGP-EVPN
distributed control plane that is based on the integrated routing
and bridging fabric overlay discussed in [RFC9135].

Underlay: An IP, MPLS, or SRv6 fabric core network that provides
routed reachability between EVPN PEs.

Overlay: L3 and L2 Virtual Private Network (VPN) and L3 VPNs that are enabled via NVO3, VXLAN, SRv6, or
MPLS service layer service-layer encapsulation.

SRv6: Segment Routing over IPv6 protocol as (as specified in [RFC8986].

* [RFC8986]).

NVO: Network Virtualization Overlay.

NVO3: Network Virtualization Overlays as over Layer 3 (as specified in [RFC8926].

*
[RFC8926]).

VXLAN: Virtual eXtensible Local Area Network as (as specified in
[RFC7348]
*
[RFC7348]).

MPLS: Multi-Protocol Multiprotocol Label Switching as (as specified in [RFC3031].

* [RFC3031]).

EVPN PE: Ethernet VPN Provider Edge. A PE switch-router switch router in an EVPN-IRB EVPN-
IRB network that runs overlay BGP-EVPN control plane planes and connects
to overlay CE host devices. An EVPN PE may also be the first-hop layer-3
L3 gateway for
CE/host CE host devices. This document refers to EVPN PE
as a logical function in an EVPN-IRB network. This EVPN PE
function may be physically hosted on a top-of-rack ToR switching device (ToR) OR or at
layer(s) above the ToR in the Clos fabric. An EVPN PE is
typically also an IP or MPLS tunnel end-point endpoint for overlay VPN
flow.

*
flows.

Symmetric EVPN-IRB: is a A specific design approach used in EVPN-
based EVPN-based
networks [RFC9135] to handle both Layer 2 (L2) L2 and Layer 3
(L3) L3 forwarding within the
same network infrastructure. The key characteristic of symmetric
EVPN-IRB is that both ingress and egress PE routers perform
routing for inter-subnet traffic.

Asymmetric EVPN-IRB: is a A design approach used in EVPN-based networks
[RFC9135] to handle Layer 2 (L2) L2 and Layer 3 (L3) L3 forwarding. In this approach, only
the ingress Provider Edge (PE) PE router performs routing for inter-subnet traffic,
while the egress PE router performs bridging.

ARP: Address Resolution Protocol [RFC826]. [RFC0826]. ARP references in this
document are equally applicable to both ARP and NDP.

NDP: IPv6 Neighbor Discovery Protocol [RFC4861].

* Ethernet-Segment: Physical (for IPv6 [RFC4861]).

ES: Ethernet Segment. A physical ethernet or LAG (Link Aggregation
Group) port that connects
an access device to an EVPN PE, as defined in [RFC7432].

MC-LAG: Multi-Chasis Multi-Chassis Link Aggregation Group.

EVPN all-active multi-homing: is a A redundancy and load-sharing
mechanism used in EVPN networks. This method allows multiple PE
devices to simultaneously provide Layer 2 L2 and Layer 3 L3 connectivity to a
single CE device or network segment.

RT-2: Route Type 2. EVPN route type 2 RT-2 carrying both MAC address and IP
address reachability as specified in [RFC7432].

RT-5: Route Type 5. EVPN route type 5 RT-5 carrying IP prefix reachability as
specified in [RFC7432].

MAC-IP address: The IPv4 and/or IPv6 address and MAC address binding
for an overlay host.

Peer-Sync-Local MAC route: The learned BGP EVPN learnt MAC route for a host
that is directly attached to a local multi-homed Ethernet Segment.

* ES.

Peer-Sync-Local MAC-IP route: The learned BGP EVPN learnt MAC-IP route for
a host that is directly attached to a local multi-homed Ethernet
Segment.

* ES.

Peer-Sync-Local MAC sequence number: Sequence The sequence number received
with a Peer-Sync-Local MAC route.

Peer-Sync-Local MAC-IP sequence number: Sequence The sequence number received
with a Peer-Sync-Local MAC-IP route.

VM: Virtual Machine or (or containerized workloads.

* workloads).

Host: Host in In this document document, generically refers to any user/CE user or CE
endpoint attached to an EVPN-IRB network network, which may be a VM,
containerized workload or a workload, physical end-point endpoint, or CE device.

3. Background and Problem Statement

3.1. Optional MAC only MAC-Only RT-2

In an EVPN-IRB scenario, scenario where a single MAC+IP RT-2 advertisement
carries both IP and MAC routes, a MAC-only RT-2 advertisement becomes
redundant for host MAC addresses already advertised via MAC+IP RT-2.
Consequently, the advertisement of a local MAC-only RT-2 is optional
at an EVPN PE. This consideration is important for mobility
scenarios discussed in subsequent sections. It is noteworthy that a
local MAC route and its assigned sequence number are still maintained
locally on a PE, and only the advertisement of this route to other
PEs is optional.

MAC-only RT-2 advertisements may still be issued for non-IP host MAC
addresses that are not included in MAC+IP RT-2 advertisements.

3.2. Mobility Use Cases

This section outlines the IRB mobility use cases addressed in this
document. Detailed procedures to handle these scenarios are provided
in Sections 6 and 7.

* A host move results in both the host's IP and MAC addresses moving
together.

* A host move results in the host's IP address moving to a new MAC
address association.

* A host move results in the host's MAC address moving to a new IP
address association.

3.2.1. Host MAC+IP Address Move

This is the baseline scenario where a host move results in both the
host's MAC and IP addresses moving together without altering the MAC-
IP address binding. The existing MAC route mobility procedures
defined in [RFC7432] can be leveraged to support this MAC+IP address
mobility scenario.

3.2.2. Host IP address Address Move to new New MAC address Address

This scenario involves a host move where the host's IP address is
reassigned to a new MAC address.

3.2.2.1. Host Reload

A host reload or orchestrated move may cause a host to be re-spawned
at the same or new PE location, resulting in a new MAC address
assignment while retaining the existing IP address. This results in
the host's IP address moving to a new MAC address binding, as shown
below:

IP-a, MAC-a ---> IP-a, MAC-b

3.2.2.2. MAC Address Sharing

This scenario considers cases where multiple hosts, each with a
unique IP address, share a common MAC address. A host move results
in a new MAC address binding for the host IP address. For example,
hosts running on a single physical server might share the same MAC
address. Alternatively, an L2 access network behind a firewall may
have all host IP addresses learned with a common firewall MAC
address. In these "shared MAC" scenarios, multiple local MAC-IP ARP/
NDP entries may be learned with the same MAC address. A host IP
address move to a new physical server could result in a new MAC
address association for the host IP.

3.2.2.3. Problem

In the aforementioned scenarios, a combined MAC+IP EVPN RT-2
advertised with a single sequence number attribute assumes a fixed
IP-to-MAC address mapping. A host IP address move to a new MAC
address breaks this assumption and results in a new MAC+IP route. If
this new route is independently assigned a new sequence number, the
sequence number can no longer determine the most recent host IP
reachability in a symmetric EVPN-IRB design or the most recent IP-to-
MAC address binding in an asymmetric EVPN-IRB design.

+------------------------+
| Underlay Network Fabric|
+------------------------+

+-----+ +-----+ +-----+ +-----+ +-----+ +-----+
| PE1 | | PE2 | | PE3 | | PE4 | | PE5 | | PE6 |
+-----+ +-----+ +-----+ +-----+ +-----+ +-----+
\ / \ / \ /
\ ESI-1 / \ ESI-2 / \ ESI-3 /
\ / \ / \ /
+\---/+ +\---/+ +\---/+
| \ / | | \ / | | \ / |
+--+--+ +--+--+ +--+--+
| | |
Server-M1 Server-M2 Server-M3
| | |
VM-IP1, VM-IP2 VM-IP3, VM-IP4 VM-IP5, VM-IP6

Figure 1

Figure 1 illustrates a topology with host VMs sharing the physical
server MAC address. In steady state, the IP1-M1 route is learned at
PE1 and PE2 and advertised to remote PEs with a sequence number N.
If VM-IP1 moves to Server-M2, ARP or NDP-based local learning at PE3
and PE4 would result in a new IP1-M2 route. If this new route is
assigned a sequence number of 0, the mobility procedure for VM-IP1
will not trigger across the overlay network.

A sequence number assignment procedure must be defined to
unambiguously determine the most recent IP address reachability, IP-
to-MAC address binding, and MAC address reachability for such MAC
address sharing scenarios.

3.2.3. Host MAC address move Address Move to new New IP address Address

This is a scenario where a host move or re-provisioning behind the
same or new PE location may result in the host getting a new IP
address assigned, assigned while keeping the same MAC address.

3.2.3.1. Problem

The complication in this scenario arises because MAC address
reachability can be carried via a combined MAC+IP route, whereas a
MAC-only route may not be advertised. Associating a single sequence
number with the MAC+IP route implicitly assumes a fixed MAC-to-IP
mapping. A MAC address move that results in a new IP address
association breaks this assumption and creates a new MAC+IP route.
If this new route independently receives a new sequence number, the
sequence number can no longer reliably indicate the most recent host
MAC address reachability.

+------------------------+
| Underlay Network Fabric|
+------------------------+
+-----+ +-----+ +-----+ +-----+ +-----+ +-----+
| PE1 | | PE2 | | PE3 | | PE4 | | PE5 | | PE6 |
+-----+ +-----+ +-----+ +-----+ +-----+ +-----+
\ / \ / \ /
\ ESI-1 / \ ESI-2 / \ ESI-3 /
\ / \ / \ /
+\---/+ +\---/+ +\---/+
| \ / | | \ / | | \ / |
+--+--+ +--+--+ +--+--+
| | |
Server1 Server2 Server3
| | |
IP1-M1, IP2-M2 IP3-M3, IP4-M4 IP5-M5, IP6-M6

Figure 2

For instance, consider that host IP1-M1 is learned locally at PE1 and
PE2 and advertised to remote hosts with sequence number N. If this
host with MAC address M1 is re-provisioned at Server2 and assigned a
different IP address (e.g., IP7), then the new IP7-M1 route learned
at PE3 and PE4 would be advertised with sequence number 0.
Consequently, L3 reachability to IP7 would be established across the
overlay, but the MAC mobility procedure for M1 would not trigger due
to the new MAC-IP route advertisement. Advertising an optional MAC-only MAC-
only route with its sequence number would trigger MAC mobility per
[RFC7432]. However, without this additional advertisement, a single
sequence number associated with a combined MAC+IP route may be
insufficient to update MAC address reachability across the overlay.

A MAC-IP route sequence number assignment procedure is required to
unambiguously determine the most recent MAC address reachability in
such
the previous scenarios without advertising a MAC-only route.

Furthermore, PE1 and PE2, upon learning new reachability for IP7-M1 via PE3 and
PE4, PE1 and PE2 must probe and delete any local IPs associated with
the MAC address M1, such as IP1-M1.

It could be argued that the MAC mobility sequence number defined in
[RFC7432] applies only to the MAC route part of a MAC-IP route, thus
covering this scenario. This interpretation could serve as a
clarification to [RFC7432] and supports the need for a common
sequence number assignment procedure across all MAC-IP mobility
scenarios detailed in this document.

3.3. EVPN All Active multi-homed Multi-Homed ES

+------------------------+
| Underlay Network Fabric|
+------------------------+

+-----+ +-----+ +-----+ +-----+
| PE1 | | PE2 | | PE3 | | PE4 |
+-----+ +-----+ +-----+ +-----+
\\ // \\ //
\\ ESI-1 // \\ ESI-2 //
\\ // \\ //
+\\---//+ +\\---//+
| \\ // | | \\ // |
+---+---+ +---+---+
| |
CEs CEs

Figure 3

Consider an EVPN-IRB overlay network illustrated in Figure 3, where
hosts are multi-homed to two or more PE devices via an all-active
multi-homed ES. MAC and ARP/NDP entries learned on a local ES may
also be synchronized across the multi-homing PE devices sharing this
ES. This synchronization enables local switching of intra- and
inter-subnet ECMP traffic flows from remote hosts. Thus, local MAC
and ARP/NDP entries on a given ES may be learned through local
learning and/or synchronization from another PE device sharing the
same ES.

For a host that is multi-homed to multiple PE devices via an all-
active ES interface, the local learning of the host MAC and MAC-IP
routes at each PE device is an independent asynchronous event,
dependent on traffic flow or an ARP/NDP response from the host
hashing to a directly connected PE on the MC-LAG interface.
Consequently, the sequence number mobility attribute value assigned
to a locally learned MAC or MAC-IP route at each device may not
always be the same, depending on transient states on the device at
the time of local learning.

For example, consider a host that is deleted from ESI-2 and moved to
ESI-1. It is possible for the host to be learned on PE1 following
the deletion of the remote route from PE3 and PE4, PE4 while being learned
on PE2 prior to the deletion of the remote route from PE3 and PE4.
In this case, PE1 would process local host route learning as a new
route and assign a sequence number of 0, while PE2 would process
local host route learning as a remote-to-local move and assign a
sequence number of N+1, where N is the existing sequence number
assigned at PE3 and PE4.

Inconsistent sequence numbers advertised from multi-homing devices:

* Creates Create ambiguity regarding how remote PEs should handle paths with
the same ESI but different sequence numbers. A remote PE might
not program ECMP paths if it receives routes with different
sequence numbers from a set of multi-homing PEs sharing the same
ESI.

* Breaks Break consistent route versioning across the network overlay that
is needed for EVPN mobility procedures to work.

For instance, in this inconsistent state, PE2 would drop a remote
route received for the same host with sequence number N (since its
local sequence number is N+1), while PE1 would install it as the best
route (since its local sequence number is 0).

To support mobility for multi-homed hosts using the sequence number
mobility attribute, local MAC and MAC-IP routes learned on a multi-
homed ES must be advertised with the same sequence number by all PE
devices to which the ES is multi-homed. There is a need for a
mechanism to ensure the consistency of sequence numbers assigned
across these PEs.

4. Design Considerations

To summarize, the sequence number assignment scheme and
implementation must consider the following:

* Synchronization Across Multi-Homing across multi-homing PE Devices: devices:

MAC+IP routes may be learned on an ES that is multi-homed to
multiple PE devices, requiring synchronized sequence numbers
across these devices.

* Optional MAC-Only MAC-only RT-2:

In an IRB scenario, MAC-only RT-2 is optional and may not be
advertised alongside MAC+IP RT-2.

* Multiple IPs Associated associated with a Single single MAC:

A single MAC address may be linked to multiple IP addresses,
indicating multiple host IPs sharing a common MAC address.

* Host IP Movement: movement:

A host IP address move may result in a new MAC address
association, necessitating a new IP address to MAC address
association and a new MAC+IP route.

* Host MAC Address Movement: address movement:

A host MAC address move may result in a new IP address
association, requiring a new MAC address to IP address association
and a new MAC+IP route.

* Local MAC-IP Route Learning route learning via ARP/NDP:

Local MAC-IP route learning via ARP/NDP always accompanies a local
MAC route learning event resulting from the ARP/NDP packet.
However, MAC and MAC-IP route learning can occur in any order.

* Separate Sequence Numbers sequence numbers for MAC and IP routes:

Use cases that do not maintain a constant 1:1 MAC-IP address
mapping across moves could potentially be addressed by using
separate sequence numbers for MAC and IP route components of the
MAC+IP route. However, maintaining two separate sequence numbers
adds significant complexity, debugging challenges, and backward
compatibility issues. Therefore, this document addresses these
requirements using a single sequence number attribute.

5. Solution Components

This section outlines the main components of the EVPN-IRB mobility
solution specified in this document. Subsequent sections will detail
the exact sequence number assignment procedures based on the concepts
described here.

5.1. Sequence Number Inheritance

The key concept presented here is to treat a local MAC-IP route as a
child of the corresponding local MAC route within the local context
of a PE. This ensures that the local MAC-IP route inherits the
sequence number attribute from the parent local MAC-only route. In
terms of object dependencies, this could be represented as the MAC-IP
route being a dependent child of the parent MAC route:

Mx-IPx -----> Mx (seq# = N)

Thus, both the parent MAC route and the child MAC-IP routes share a
common sequence number associated with the parent MAC route. This
ensures that a single sequence number attribute carried in a combined
MAC+IP route represents the sequence number for both a MAC-only route
and a MAC+IP route, making the advertisement of the MAC-only route
truly optional. This enables a MAC address to assume a different IP
address upon moving and still establish the most recent reachability
to the MAC address across the overlay network via the mobility
attribute associated with the MAC+IP route advertisement. For
instance, when Mx moves to a new location, it would be assigned a
higher sequence number at its new location per [RFC7432]. If this
move results in Mx assuming a different IP address, IPz, the local
Mx+IPz route would inherit the new sequence number from Mx.

Local MAC and local MAC-IP routes are typically sourced from data
plane learning and ARP/NDP learning, respectively, and can be learned
in the control plane in any order. Implementation Implementations can either
replicate the inherited sequence number in each MAC-IP entry or
maintain a single attribute in the parent MAC route by creating a
forward reference local MAC object for cases where a local MAC-IP
route is learned before the local MAC route.

5.2. MAC Address Sharing

For the shared MAC address scenario, multiple local MAC-IP sibling
routes inherit the sequence number attribute from the common parent
MAC route:

Figure 4

In such cases, a host-IP move to a different physical server results
in the IP moving to a new MAC address binding. A new MAC-IP route
resulting from this move must be advertised with a sequence number
higher than the previous MAC-IP route for this IP, advertised from
the prior location. For example, consider a route Mx-IPx currently
advertised with sequence number N from PE1. If IPx moves to a new
physical server behind PE2 and is associated with MAC Mz, the new
local Mz-IPx route must be advertised with a sequence number higher
than N and higher than the previous Mz sequence number M. This
allows PE devices, including PE1, PE2, and other remote PE devices,
to determine and program the most recent MAC address binding and
reachability for the IP. PE1, upon receiving this new Mz-IPx route
with sequence number N+1 or M+1 (whichever is greater), would update
IPx reachability via PE2 for symmetric IRB and update IPx's ARP/NDP
binding to Mz for asymmetric IRB, IRB while clearing and withdrawing the
stale Mx-IPx route with the lower sequence number.

This implies that the sequence number associated with the local MAC
route Mz and all local MAC-IP child routes of Mz at PE2 must be
incremented to N+1 or M+1 if the previous Mz sequence number M is
greater than N and is re-advertised across the overlay. While this
re-advertisement of all local MAC-IP children routes affected by the
parent MAC route adds overhead, it also avoids the need for
maintaining and advertising two separate sequence number attributes
for IP and MAC route components of MAC+IP RT-2. Implementation Implementations must
be able to look up MAC-IP routes for a given IP and update the
sequence number for its parent MAC route and for its MAC-IP route
children.

5.3. Sequence Number Synchronization

To support mobility for multi-homed hosts, local MAC and MAC-IP
routes learned on a shared ES must be advertised with the same
sequence number by all PE devices to which the ES is multi-homed.
This applies to local MAC-only routes as well. MAC and MAC-IP routes
for a host that is attached to a local ES may be learned natively via
data plane and ARP/NDP ARP/NDP, respectively, as well as via BGP EVPN from
another multi-homing PE to achieve local switching. MAC and MAC-IP
routes learnt learned natively via data plane and ARP/NDP are respectively
referred to as Local local MAC routes and Local local MAC-IP routes. BGP EVPN
learnt
learned MAC and MAC-IP routes for a host that is attached to a local
ES are respectively referred to as Peer-Sync-Local MAC routes and
Peer-Sync-Local MAC-IP routes as they are effectively local routes
synchronized from a multi-homing peer. Local and Peer-Sync-Local
route learning can occur in any order. Local MAC-IP routes
advertised by all multi-homing PE devices sharing the ES must carry
the same sequence number, independent of the order in which they are
learned. This implies: implies that:

* On local or Peer-Sync-Local MAC-IP route learning, the sequence
number for the local MAC-IP route must be compared and updated to
the higher value.

* On local or Peer-Sync-Local MAC route learning, the sequence
number for the local MAC route must be compared and updated to the
higher value.

If an update to the local MAC-IP route sequence number is required as
a result of the comparison with the Peer-Sync-Local MAC-IP route, it
essentially amounts to a sequence number update on the parent local
MAC route, resulting in an inherited sequence number update on the
Local
local MAC-IP route.

6. Methods for Sequence Number Assignment

The following sections specify the sequence number assignment
procedures required for local and Peer-Sync-Local MAC and MAC-IP
route learning events to achieve the objectives outlined. outlined objectives.

6.1. Local MAC-IP learning Learning

A local Mx-IPx learning via ARP or NDP should result in the
computation or re-computation of the parent MAC route Mx's sequence
number, following which the MAC-IP route Mx-IPx inherits the parent
MAC route's sequence number. The parent MAC route Mx sequence number
MUST be computed as follows:

* It MUST be higher than any existing remote MAC route for Mx, as
per [RFC7432].

* It MUST be at least equal to the corresponding Peer-Sync-Local MAC
route sequence number, if present.

* If It MUST be higher than the "Mz" sequence number if the IP is also
associated with a different remote MAC "Mz," it
MUST be higher than the "Mz" sequence number. "Mz".

Once the new sequence number for the MAC route Mx is computed as per
the above criteria, all local MAC-IP routes associated with MAC Mx
MUST inherit the updated sequence number.

6.2. Local MAC learning Learning

The local MAC route Mx Sequence sequence number MUST be computed as follows:

* It MUST be higher than any existing remote MAC route for Mx, as
per [RFC7432].

* It MUST be at least equal to the corresponding Peer-Sync-Local MAC
route sequence number if one is present.

If the existing local MAC route sequence number is less than the
Peer-Sync-Local MAC route sequence number, then the PE MUST update
the local MAC route sequence number to be equal to the Peer-Sync-Local Peer-Sync-
Local MAC route sequence number.

If the existing local MAC route sequence number is equal to or
greater than the Peer-Sync-Local MAC route sequence number, no
update is required to the local MAC route sequence number.

Once the new sequence number for the MAC route Mx is computed as per
the above criteria, all local MAC-IP routes associated with the MAC
route Mx MUST inherit the updated sequence number. Note that the
local MAC route sequence number might already be present if there was
a local MAC-IP route learned prior to the local MAC route, in which case route. In this
case, the above may not result in any change in the local MAC route
sequence number.

6.3. Remote MAC or MAC-IP Route Update

Upon receiving a remote MAC or MAC-IP route update associated with a
MAC address Mx with a sequence number that is: is either:

* Either higher than the sequence number assigned to a local route for MAC Mx,
Mx or

* Or equal to the sequence number assigned to a local route for MAC Mx,
but the remote route is selected as best due to a lower VTEP VXLAN
Tunnel End Point (VTEP) IP as per [RFC7432],

the following actions are REQUIRED on the receiving PE:

* The PE MUST trigger a probe and deletion procedure for all local
MAC-IP routes associated with MAC Mx.

* The PE MUST trigger a deletion procedure for the local MAC route
for Mx.

6.4. Peer-Sync-Local MAC route update Route Update

Upon receiving a Peer-Sync-Local MAC route, the corresponding local
MAC route Mx sequence number (if present) should be re-computed as
follows:

* If the current sequence number is less than the received Peer-
Sync-Local MAC route sequence number, it MUST be increased to be
equal to the received Peer-Sync-Local MAC route sequence number.

* If a local MAC route sequence number is updated as a result of the
above, all local MAC-IP routes associated with MAC route Mx MUST
inherit the updated sequence number.

6.5. Peer-Sync-Local MAC-IP route update

Receiving Route Update

Because the MAC-only RT-2 advertisement is optional, receiving a
Peer-Sync-Local MAC-IP route for a locally attached host results in a
derived Peer-Sync-Local MAC Mx route entry as the MAC-
only RT-2 advertisement is optional. entry. The corresponding local
MAC Mx route sequence number (if present) should be re-computed as
follows:

* If the current sequence number is less than the received Peer-
Sync-Local MAC route sequence number, it MUST be increased to be
equal to the received Peer-Sync-Local MAC route sequence number.

* If a local MAC route sequence number is updated as a result of the
above, all local MAC-IP routes associated with MAC route Mx MUST
inherit the updated sequence number.

6.6. Interoperability

Generally, if all PE nodes in the overlay network follow the above
sequence number assignment procedures and the PE is advertising both
MAC+IP and MAC routes, the sequence numbers advertised with the MAC
and MAC+IP routes with the same MAC address would always be the same.
However, an interoperability scenario with a different implementation
could arise, where a non-compliant PE implementation assigns and
advertises independent sequence numbers to MAC and MAC+IP routes. To
handle this case, if different sequence numbers are received for
remote MAC+IP routes and corresponding remote MAC routes from a
remote PE, the sequence number associated with the remote MAC route
MUST be computed and interpreted as:

* The highest of all received sequence numbers with remote MAC+IP
and MAC routes with the same MAC address.

* The MAC route sequence number would be re-computed on a MAC or
MAC+IP route withdraw as per the above.

A MAC and/or IP address move to the local PE would then result in the
MAC (and hence all MAC-IP) route sequence numbers being incremented
from the above computed remote MAC route sequence number.

If MAC-only routes are not advertised at all, and different sequence
numbers are received with multiple MAC+IP routes for a given MAC
address, the sequence number associated with the derived remote MAC
route should still be computed as the highest of all received MAC+IP
route sequence numbers with the same MAC address.

Note that it is not required for a PE to maintain explicit knowledge
of a remote PE being compliant or non-compliant with this
specification as long as it implements the above logic to handle
remote sequence numbers that are not synchronized between MAC route
and MAC-IP route(s) for the same remote MAC address.

6.7. MAC Address Sharing Race Condition

In a MAC address sharing use case described in section Section 5.2, a race
condition is possible with simultaneous host moves between a pair of
PEs. Example The example scenario below illustrates this race condition and
its remediation:

* PE1 with locally attached host IPs I1 and I2 that share MAC
address M1. PE1 as As a result result, PE1 has local MAC-IP routes I1-M1 and
I2-M1.

* PE2 with locally attached host IPs I3 and I4 that share MAC
address M2. PE2 as As a result result, PE2 has local MAC-IP routes I3-M2 and
I4-M2.

* A simultaneous move of I1 from PE1 to PE2 and of I3 from PE2 to
PE1 will cause I1's MAC address to change from M1 to M2 and cause
I3's MAC address to change from M2 to M1.

* Route I3-M1 may be learnt learned on PE1 before I1's local entry I1-M1
has been probed out on PE1 and/or route I1-M2 may be learnt learned on
PE2 before I3's local entry I3-M2 has been probed out on PE2.

* In such a scenario, MAC route sequence number assignment rules
defined in section Section 6.1 will cause new mac-ip MAC-IP routes I1-M2 and
I3-M1 to bounce between PE1 and PE2 with seuence sequence number
increments until stale entries I1-M1 and I3-M2 have been probed
out from PE1 and PE2 PE2, respectively.

An implementation MUST ensure proper probing procedures to remove
stale ARP, NDP, and local MAC entries, following a move, on learning
remote routes as defined in section Section 6.3 (and as per [RFC9135]) to
minimize exposure to this race condition.

6.8. Mobility Convergence

This section is optional and details ARP and NDP probing procedures
that MAY be implemented to achieve faster host re-learning relearning and
convergence on mobility events. PE1 and PE2 are used as two example
PEs in the network to illustrate the mobility convergence scenarios
in this section.

* Following a host move from PE1 to PE2, the host's MAC address is
discovered at PE2 as a local MAC route via data frames received
from the host. If PE2 has a prior remote MAC-IP host route for
this MAC address from PE1, an ARP/NDP probe MAY be triggered at
PE2 to learn the MAC-IP address as a local adjacency and trigger
EVPN RT-2 advertisement for this MAC-IP address across the overlay
with new reachability via PE2. This results in a reliable "event-
based" host IP learning triggered by a "MAC address learning
event" across the overlay, and hence hence, a faster convergence of
overlay routed flows to the host.

* Following a host move from PE1 to PE2, once PE1 receives a MAC or
MAC-IP route from PE2 with a higher sequence number, an ARP/NDP
probe MAY be triggered at PE1 to clear the stale local MAC-IP
neighbor adjacency or to re-learn relearn the local MAC-IP in case the host
has moved back or is duplicated.

* Following a local MAC route age-out, if there is a local IP
adjacency with this MAC address, an ARP/NDP probe MAY be triggered
for this IP to either re-learn relearn the local MAC route and maintain
local L3 and L2 reachability to this host or to clear the ARP/NDP
entry if the host is no longer local. This accomplishes the
clearance of stale ARP/NDP entries triggered by a MAC age-out
event even when the ARP/NDP refresh timer is longer than the MAC
age-out timer. Clearing stale IP neighbor entries facilitates
traffic convergence if the host was silent and not discovered at
its new location. Once the stale neighbor entry for the host is
cleared, routed traffic flow destined for the host can re-trigger
ARP/NDP discovery for this host at the new location.

6.8.1. Generalized Probing Logic

The above probing logic may be generalized as probing for an IP
neighbor anytime a resolving parent MAC route is inconsistent with
the MAC-IP neighbor route, where inconsistency is defined as being
not present or conflicting in terms of the route source being local
or remote. The MAC-IP route to parent MAC route relationship
described in section Section 5.1 MAY be used to achieve this logic.

7. Routed Overlay

An additional use case involves traffic to an end host in the overlay
being entirely IP routed. In such a purely routed overlay:

* A host MAC route is never advertised in the EVPN overlay control
plane.

* Host /32 or /128 IP reachability is distributed across the overlay
via EVPN Route Type 5 (RT-5) along with a zero or non-zero ESI.

* An overlay IP subnet may still be stretched across the underlay
fabric. However, intra-subnet traffic across the stretched
overlay is never bridged.

* Both inter-subnet and intra-subnet traffic in the overlay is IP
routed at the EVPN PE.

Please refer to [RFC7814] for more details.

Host mobility within the stretched subnet still needs support. In
the absence of host MAC routes, the sequence number mobility Extended
Community specified in [RFC7432] section Section 7.7 of [RFC7432] MAY be associated
with a /32 or /128 host IP prefix advertised via EVPN Route Type 5.
MAC mobility procedures defined in [RFC7432] can be applied to host
IP prefixes as follows:

* On local learning of a host IP on a new ESI, the host IP MUST be
advertised with a sequence number higher than what is currently
advertised with the old ESI.

* On receiving a host IP route advertisement with a higher sequence
number, a PE MUST trigger ARP/NDP probe and deletion procedures on
any local route for that IP with a lower sequence number. The PE
will update the forwarding entry to point to the remote route with
a higher sequence number and send an ARP/NDP probe for the local
IP route. If the IP has moved, the probe will time out, and the
local IP host route will be deleted.

Note that there is only one sequence number associated with a host
route at any time. For previous use cases where a host MAC address
is advertised along with the host IP address, a sequence number is
only associated with the MAC address. If the MAC is not advertised,
as in this use case, a sequence number is associated with the host IP
address.

This mobility procedure does not apply to "anycast IPv6" "anycast" IPv6 hosts
advertised via NA Neighbor Advertisement (NA) messages with the Override
Flag (O Flag) set to 0. Refer to [RFC9161] for more details.

8. Duplicate Host Detection

Duplicate host detection scenarios across EVPN-IRB can be classified
as follows:

* Scenario A: Two hosts have the same MAC address (host IPs may or
may not be duplicates).

* Scenario B: Two hosts have the same IP address but different MAC
addresses.

* Scenario C: Two hosts have the same IP address, and the host MAC
address is not advertised.

As specified in [RFC9161], Duplicate duplicate detection procedures for
Scenarios B and C do not apply to "anycast IPv6" "anycast" IPv6 hosts advertised via
NA messages with the Override Flag (O Flag) set to 0.

8.1. Scenario A

In cases where duplicate hosts share the same MAC address, the MAC
address is detected as duplicate using the duplicate MAC address
detection procedure described in [RFC7432]. Corresponding MAC-IP
routes with the same MAC address do not require separate duplicate
detection and MUST inherit the duplicate property from the MAC route.
If a MAC route is marked as duplicate, all associated MAC-IP routes
MUST also be treated as duplicates. Duplicate detection procedures
need only be applied to MAC routes.

8.2. Scenario B

Misconfigurations may lead to different MAC addresses being assigned
the same IP address. This scenario is not detected by [RFC7432] the duplicate
MAC address detection procedures from [RFC7432] and can result in
incorrect routing of traffic destined for the IP address.

Such situations, when detected locally, are identified as a move
scenario through the local MAC route sequence number computation
procedure described in section Section 6.1:

* If the IP is associated with a different remote MAC "Mz," "Mz", the
sequence number MUST be higher than the "Mz" sequence number.

This move results in a sequence number increment for the local MAC
route due to the remote MAC-IP route being associated with a
different MAC address, counting which counts as an "IP move" against the IP,
independent of the MAC. The duplicate detection procedure described
in [RFC7432] can then be applied to the IP entity independent of the
MAC. Once an IP is detected as duplicate, the corresponding MAC-IP
route should be treated as duplicate. Associated MAC routes and any
other MAC-IP routes related to this MAC should not be affected.

8.2.1. Duplicate IP Detection Procedure for Scenario B

The duplicate IP detection procedure for this scenario is specified
in [RFC9161]. An "IP move" is further clarified as follows:

* Upon learning a local MAC-IP route Mx-IPx, check for existing
remote or local routes for IPx with a different MAC address
association (Mz-IPx). If found, count this as an "IP move" for
IPx, independent of the MAC.

* Upon learning a remote MAC-IP route Mz-IPx, check for existing
local routes for IPx with a different MAC address association (Mx-
IPx). If found, count this as an "IP move" for IPx, independent
of the MAC.

A MAC-IP route MUST be treated as duplicate if either:

* The the corresponding MAC route is marked as duplicate via the
existing detection procedure. procedure, or

* The the corresponding IP is marked as duplicate via the extended
procedure described above.

8.3. Scenario C

As described in Section 7, in a purely routed overlay scenario, as described in section 7, scenario where
only a host IP is advertised via EVPN RT-5 with a sequence number
mobility attribute, procedures similar to the duplicate MAC address
detection procedures specified in [RFC7432] can be applied to IP-only
host routes for duplicate IP detection as follows:

* Upon learning a local host IP route IPx, check for existing remote
or local routes for IPx with a different ESI association. If
found, count this as an "IP move" for IPx.

* Upon learning a remote host IP route IPx, check for existing local
routes for IPx with a different ESI association. If found, count
this as an "IP move" for IPx.

* Using configurable parameters "N" and "M," "M", if "N" IP moves are
detected within "M" seconds for IPx, then IPx should be treated as
duplicate.

8.4. Duplicate Host Recovery

Once a MAC or IP address is marked as duplicate and frozen,
corrective action must be taken to un-provision one of the duplicate
MAC or IP addresses. Un-provisioning refers to corrective action
taken on the host side. Following this correction, normal operation
will not resume until the duplicate MAC or IP address ages out out,
unless additional action is taken to expedite recovery.

Possible additional corrective actions for faster recovery include: are
outlined in the following sections.

8.4.1. Route Un-freezing Unfreezing Configuration

Unfreezing the duplicate or frozen MAC or IP route via a CLI can be
used to recover from the duplicate and frozen state following
corrective un-provisioning of the duplicate MAC or IP address.
Unfreezing the MAC or IP route should result in advertising it with a
sequence number higher than that advertised from the other location.

Two scenarios exist:

* Scenario A: The duplicate MAC or IP address is un-provisioned at
the location where it was not marked as duplicate.

* Scenario B: The duplicate MAC or IP address is un-provisioned at
the location where it was marked as duplicate.

Unfreezing the duplicate and frozen MAC or IP route will result in
recovery to a steady state as follows:

* Scenario A: If the duplicate MAC or IP address is un-provisioned
at the non-duplicate location, unfreezing the route at the frozen
location results in advertising with a higher sequence number,
leading to automatic clearing of the local route at the un-
provisioned location via ARP/NDP PROBE and DELETE procedures.

* Scenario B: If the duplicate host is un-provisioned at the
duplicate location, unfreezing the route triggers an advertisement
with a higher sequence number to the other location, prompting re-
learning
relearning and clearing of the local route at the original
location upon receiving the remote route advertisement.

Probes

The probes referred to in these scenarios are event-driven probes
resulting from receiving a route with a higher sequence number.
Periodic probes resulting from refresh timers may also occur
independently.

8.4.2. Route Clearing Configuration

In addition to the above, route clearing CLIs may be used to clear
the local MAC or IP route after the duplicate host is un-provisioned:

* Clear MAC CLI: Used to clear a duplicate MAC route.

* Clear ARP/NDP: Used to clear a duplicate IP route.

The route unfreeze CLI may still need to be executed if the route was
un-provisioned and cleared from the non-duplicate location. Given
that unfreezing the route via the CLI would result in auto-clearing
from the un-provisioned location, as explained earlier, using a route
clearing CLI for recovery from the duplicate state is optional.

9. Security Considerations

Security

The security considerations discussed in [RFC7432] and [RFC9135]
apply to this document. Methods described in this document further
extend the consumption of sequence numbers for IRB deployments. They
Hence, they are hence subject to the same considerations if the control
plane or data plane was to be compromised. As an example, if host facing the
host-facing data plane is compromised, spoofing attempts could result
in a legitimate host being perceived as moved, eventually resulting
in the host being marked as duplicate. Considerations The considerations for
protecting control and data
plane planes described in [RFC7432] are equally
applicable to such mobility spoofing use cases.

10. IANA Considerations

This document has no IANA actions required. actions.

11. Contributors

Gunter van de Velde
Nokia
Email: van_de_velde@nokia.com

Wen Lin
Juniper
Email: wlin@juniper.net

Sonal Agarwal
Arrcus
Email: sonal@arrcus.com

12. Acknowledgements

Authors would like to thank Gunter van de Velde for significant
contribution to improve the readability of this document. Authors
would also like to thank Sonal Agarwal and Larry Kreeger for multiple
contributions through the implementation process. Authors would like
to thank Vibov Bhan and Patrice Brissette for early feedback during
implementation and testing of several procedures defined in this
document. Authors would like to thank Wen Lin for a detailed review
and valuable comments related to MAC sharing race conditions.
Authors would also like to thank Saumya Dikshit for a detailed review
and valuable comments across the document.

13. References

13.1.

11.1. Normative References

[RFC0826] Plummer, D., "An Ethernet Address Resolution Protocol: Or
Converting Network Protocol Addresses to 48.bit Ethernet
Address for Transmission on Ethernet Hardware", STD 37,
RFC 826, DOI 10.17487/RFC0826, November 1982,
<https://www.rfc-editor.org/info/rfc826>.

[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>.

[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007, <https://www.rfc-editor.org/rfc/rfc4861>.
<https://www.rfc-editor.org/info/rfc4861>.

[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://datatracker.ietf.org/doc/html/rfc7432>. <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/rfc/rfc8174>.

[RFC826] Plummer, D., "An Ethernet Address Resolution Protocol",
RFC 826, November 1982,
<https://www.rfc-editor.org/rfc/rfc826>. <https://www.rfc-editor.org/info/rfc8174>.

[RFC9135] Sajassi, A., Salam, S., Thoria, S., Drake, J., and J.
Rabadan, "Integrated Routing and Bridging in EVPN", Ethernet VPN
(EVPN)", RFC 9135, DOI 10.17487/RFC9135, October 2021,
<https://www.rfc-editor.org/rfc/rfc9135>.
<https://www.rfc-editor.org/info/rfc9135>.

[RFC9161] Rabadan, J., Ed., Sathappan, S., Nagaraj, K., Hankins, G.,
and T. King, "Operational Aspects of Proxy-ARP/ND Proxy ARP/ND in EVPN
Ethernet Virtual Private Networks", RFC 9161,
DOI 10.17487/RFC9161, January 2022,
<https://www.rfc-editor.org/rfc/rfc9161>.

13.2.
<https://www.rfc-editor.org/info/rfc9161>.

11.2. Informative References

[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031,
DOI 10.13031/RFC3031, 10.17487/RFC3031, January 2001,
<https://datatracker.ietf.org/doc/html/rfc3031>.
<https://www.rfc-editor.org/info/rfc3031>.

[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 10.17348/RFC7348, 10.17487/RFC7348, August 2014,
<https://datatracker.ietf.org/doc/html/rfc7348>.
<https://www.rfc-editor.org/info/rfc7348>.

[RFC7814] Xu, X., Jacquenet, C., Raszuk, R., Boyes, T., and B. Fee,
"Virtual Subnet: A BGP/MPLS IP VPN-Based Subnet Extension
Solution", RFC 7814, DOI 10.17487/RFC7814, March 2016,
<https://tools.ietf.org/html/rfc7814>.
<https://www.rfc-editor.org/info/rfc7814>.

[RFC8926] Gross, J., Ed., Ganga, I., Ed., and T. Sridhar, Ed.,
"Geneve: Generic Network Virtualization Encapsulation",
RFC 8926, DOI 10.18926/RFC8926, 10.17487/RFC8926, November 2020,
<https://datatracker.ietf.org/doc/rfc8926/>.
<https://www.rfc-editor.org/info/rfc8926>.

[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. LI, Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.18986/RFC8986, 10.17487/RFC8986, February 2021,
<https://datatracker.ietf.org/doc/rfc8986/>.
<https://www.rfc-editor.org/info/rfc8986>.

Acknowledgements

The authors would like to thank Gunter Van de Velde for the
significant contributions to improve the readability of this
document. The authors would also like to thank Sonal Agarwal and
Larry Kreeger for multiple contributions through the implementation
process. The authors would like to thank Vibov Bhan and Patrice
Brissette for early feedback during the implementation and testing of
several procedures defined in this document. The authors would like
to thank Wen Lin for a detailed review and valuable comments related
to MAC sharing race conditions. The authors would also like to thank
Saumya Dikshit for a detailed review and valuable comments across the
document.

Contributors

Gunter Van de Velde
Nokia
Email: van_de_velde@nokia.com

Wen Lin
Juniper
Email: wlin@juniper.net

Sonal Agarwal
Arrcus
Email: sonal@arrcus.com

Authors' Addresses

Neeraj Malhotra (editor)
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
United States of America
Email: nmalhotr@cisco.com

Ali Sajassi
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
United States of America
Email: sajassi@cisco.com

Aparna Pattekar
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
United States of America
Email: apjoshi@cisco.com

Jorge Rabadan
Nokia
777 E. Middlefield Road
Mountain View, CA 94043
United States of America
Email: jorge.rabadan@nokia.com

Avinash Lingala
AT&T
3400 W Plano Pkwy
Plano, TX 75075
United States of America
Email: ar977m@att.com

John Drake
Juniper Networks
Email: jdrake@juniper.net