Internet Engineering Task Force (IETF) A. Sajassi
Request for Comments: 9784 P. Brissette
Category: Standards Track Cisco Systems
ISSN: 2070-1721 R. Schell
Verizon
J. Drake
Juniper
J. Rabadan
Nokia
May 2025
EVPN
Virtual Ethernet Segments for EVPN and Provider Backbone Bridge EVPN
Abstract
Ethernet VPN (EVPN) and Provider Backbone Bridge EVPN (PBB-EVPN)
introduce a comprehensive suite of solutions for delivering Ethernet
services over MPLS/IP networks. These solutions offer advanced
multi-homing
multihoming capabilities. Specifically, they support Single-Active
and All-Active redundancy modes for an Ethernet Segment (ES), which
is defined as a collection of physical links connecting a multi-homed multihomed
device or network to a set of Provider Edge (PE) devices. This
document extends the concept of an Ethernet Segment ES by allowing an ES to be
associated with a set of Ethernet Virtual Circuits (EVCs), such as
VLANs, or other entities, including MPLS Label Switched Paths (LSPs)
or pseudowires (PWs). This extended concept is referred to as
virtual Ethernet Segments (vESes). This document lists the
requirements and specifies the necessary extensions to support vES in
both EVPN and PBB-EVPN.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for 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 this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9784.
Copyright Notice
Copyright (c) 2025 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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Table of Contents
1. Introduction
1.1. Requirements Language
1.2. vESes in Access Ethernet Networks
1.3. vESes in Access MPLS Networks
2. Terminology
3. Requirements
3.1. Single-Homed and Multi-Homed Multihomed vES
3.2. Local Switching
3.3. EVC Service Types
3.4. Designated Forwarder (DF) Election
3.5. EVC Monitoring
3.6. Failure and Recovery
3.7. Fast Convergence
4. Solution Overview
4.1. EVPN DF Election for vES
4.2. Grouping and Route Coloring for vES
4.2.1. EVPN Route Coloring for vES
4.2.2. PBB-EVPN Route Coloring for vES
5. Failure Handling and Recovery
5.1. EVC Failure Handling for Single-Active vES in EVPN
5.2. EVC Failure Handling for a Single-Active vES in PBB-EVPN
5.3. Port Failure Handling for Single-Active vESes in EVPN
5.4. Port Failure Handling for Single-Active vESes in PBB-EVPN
5.5. Fast Convergence in EVPN and PBB-EVPN
6. Security Considerations
7. IANA Considerations
8. References
8.1. Normative References
8.2. Informative References
Acknowledgements
Authors' Addresses
1. Introduction
Ethernet VPN (EVPN) [RFC7432] and Provider Backbone Bridge EVPN (PBB-
EVPN) [RFC7623] introduce a comprehensive suite of solutions for
delivering Ethernet services over MPLS/IP networks. These solutions
offer advanced multi-homing multihoming capabilities. Specifically, they support
Single-Active and All-Active redundancy modes for an Ethernet Segment
(ES). As defined in [RFC7432], an ES represents a collection of
Ethernet links that connect a customer site to one or more Provider
Edge (PE) devices.
This document extends the concept of an Ethernet Segment ES by allowing an ES to be
associated with a set of Ethernet Virtual Circuits (EVCs) (such as
VLANs) or other entities, including MPLS Label Switched Paths (LSPs)
or pseudowires (PWs). This extended concept is referred to as
virtual Ethernet Segments (vESes). This document lists the
requirements and specifies the necessary extensions to support vES in
both EVPN and PBB-EVPN. The scope of this document includes PBB-EVPN
[RFC7623], EVPN over MPLS [RFC7432], and EVPN over IP [RFC8365];
however, it excludes EVPN over SRv6 [RFC9252].
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.
1.2. vESes in Access Ethernet Networks
Some service providers (SPs) seek to extend the concept of physical
Ethernet links in an ES to encompass EVCs, wherein multiple EVCs
(such as VLANs) can be aggregated onto a single physical External
Network-Network Interface (ENNI). An ES composed of a set of EVCs
rather than physical links is referred to as a vES. Figure 1
illustrates two PE devices (PE1 and PE2), each with an ENNI
aggregating several EVCs. Some of these EVCs on a given ENNI can be
associated with vESes. For instance, the multi-homed multihomed vES depicted in
Figure 1 consists of EVC4 on ENNI1 and EVC5 on ENNI2.
Third-Party
+-----+ EAP
| CE11|EVC1 +---------+
+-----+ \ | | +---+
Cust. A \-0=========0--ENNI1| |
+-----+ | | ENNI1| | +-------+ +---+
| CE12|EVC2--0=========0--ENNI1|PE1|---| | | |
+-----+ | | ENNI1| | |SP |---|PE3|-
| ==0--ENNI1| | |IP/MPLS| | | \ +---+
+-----+ | / | +---+ |Core | +---+ \-| |
| CE22|EVC3--0==== / | |Network| |CE4|
+-----+ | X | | | +---+ | |
Cust. B | / \ | +---+ | | | | /-| |
+-----+ -0=== ===0--ENNI2| | | |---|PE4|-/ +---+
| CE3 |EVC4/ | | ENNI2|PE2|---| | | |
| |EVC5--0=========0--ENNI2| | +-------+ +---+
+-----+ | | +---+
Cust. C +---------+ /\
/\ ||
|| ENNI
EVCs Interface
<--------802.1Q----------> <---- EVPN Network -----> <-802.1Q->
Figure 1: A Dual-Homed Device/Network (Both SA/AA) and SH That is
Single-Homed on the Same ENNI
ENNIs are commonly used to reach remote customer sites via
independent Ethernet access networks or third-party Ethernet Access
Providers (EAPs). ENNIs can aggregate traffic from many vESes (e.g.,
hundreds to thousands), where each vES is represented by its
associated EVC on that ENNI. As a result, ENNIs and their associated
EVCs are key elements of SP external boundaries that are carefully
designed and closely monitored. As a reminder, the ENNI is the
demarcation between the SP (IP/MPLS core network) and the third-party
Ethernet Access Provider.
To meet customers' Service Level Agreements (SLAs), SPs build
redundancy via multiple EVPN PEs and across multiple ENNIs (as shown
in Figure 1), where a given vES can be multi-homed multihomed to two or more EVPN
PE devices (on two or more ENNIs) via their associated EVCs. Just
like physical ESs in the solutions described in [RFC7432] and
[RFC7623], these vESes can be single-homed or multi-homed multihomed ESs, and
when multi-homed, multihomed, they can operate in either Single-Active or All-
Active redundancy modes. In a typical SP external-boundary scenario
(e.g., with an EAP), an ENNI can be associated with several thousands
of single-homed vESes, several hundreds of Single-Active vESes, and
tens or hundreds of All-Active vESes. The specific figures used
throughout this document reflect the relative quantities (hundreds,
thousands, etc.) of various elements as understood at the time of
writing.
1.3. vESes in Access MPLS Networks
Other SPs want to extend the concept of physical links in an ES to
individual PWs or to MPLS LSPs in Access MPLS networks, i.e., a vES
consisting of a set of PWs or a set of LSPs. Figure 2 illustrates
this concept.
MPLS Aggregation
Network
+-----+ +-----------------+
| CE11|EVC1 | |
+-----+ \ +AG1-+ PW1 +-+---+
Cust. A -0----|===========| |
+-----+ | ---+===========| | +-------+ +---+
| CE12|EVC2-0/ | PW2 /\ | PE1 +---+ | | |
+-----+ ++---+ /=||=| | | +---+PE3+-
| //=||=| | |IP/MPLS| | | \ +---+
| // \/ +-+---+ |Core | +---+ \-+ |
+-----+EVC3 | PW3// LSP1 | |Network| |CE4|
| CE13| \+AG2-+==// | | | +---+ | |
+-----+ 0 |==/PW4 /\ +-+---+ | | | | /-+ |
0 |==PW5===||=| | | +---+PE4+-/ +---+
+-----+ /++---+==PW6===||=| PE2 +---+ | | |
| CE14|EVC4 | \/ | | +-------+ +---+
+-----+ | LSP2+-+---+
Cust. C +-----------------+
/\
||
EVCs
<--802.1Q--> <-----MPLS Agg----> <--- EVPN Network ---> <-802.1Q->
Figure 2: A Dual-Homed and Single-Homed Network on MPLS
Aggregation Networks
In certain scenarios, SPs utilize MPLS Aggregation Networks that are
managed by separate administrative entities or third-party
organizations to gain access to their own IP/MPLS core network
infrastructure. This situation is depicted in Figure 2.
In such scenarios, a vES is defined as a set of individual PWs when
aggregation is not feasible. If aggregation is possible, the vES can
be associated with a group of PWs that share the same unidirectional
LSP pair, where the LSP pair consists of the ingress and egress LSPs
between the same endpoints.
In Figure 2, EVC3 is connected to a VPWS instance in AG2 that is
connected to PE1 and PE2 via PW3 and PW5, respectively. EVC4 is
connected to another VPWS instance on AG2 that is connected to PE1
and PE2 via PW4 and PW6, respectively. Since the PWs for the two
VPWS instances can be aggregated into the same LSP pair going to and
coming from the MPLS network, a common vES can be defined for the
four mentioned PWs. In Figure 2, LSP1 and LSP2 represent the two LSP
pairs between PE1 and AG2 and between PE2 and AG2, respectively. The
vES consists of these two LSP pairs (LSP1 and LSP2), and each LSP
pair has two PWs. This vES will be shared by two separate EVPN
instances (e.g., EVI-1 and EVI-2) in the EVPN network. PW3 and PW4
are associated with EVI-1 and EVI-2, respectively, on PE1, and PW5
and PW6 are associated with EVI-1 and EVI-2, respectively, on PE2.
In some cases, the aggregation of PWs that share the same LSP pair
may not be possible. For instance, if PW3 were terminated into a
third PE, e.g., PE3, instead of PE1, the vES would need to be defined
on a per individual each PW on each PE.
For MPLS/IP access networks where a vES represents a set of LSP pairs
or a set of PWs, this document extends the Single-Active multi-homing multihoming
procedures defined in [RFC7432] and [RFC7623] to accommodate vES.
The extension of vES to support All-Active multi-homing multihoming in MPLS/IP
access networks is beyond the scope of this document.
This document defines the concept of a vES and specifies the
additional extensions necessary to support a vES in accordance with
[RFC7432] and [RFC7623]. Section 3 enumerates the set of
requirements for a vES. Section 4 details the extensions for a vES
applicable to EVPN solutions, including those specified in [RFC7432]
and [RFC7209]. These extensions are designed to meet the
requirements listed in Section 3. Section 4 also provides an
overview of the solution, while Section 5 addresses failure handling,
recovery, scalability, and fast convergence of [RFC7432] and
[RFC7623] for vESes.
2. Terminology
AC: Attachment Circuit
B-MAC: Backbone MAC Address
CE: Customer Edge
C-MAC: Customer/Client MAC Address
DF: Designated Forwarder
ENNI: External Network-Network Interface
ES: Ethernet Segment
ESI: Ethernet Segment Identifier
Ethernet A-D: Ethernet Auto-Discovery
EVC: Ethernet Virtual Circuit [MEF63]
EVI: EVPN Instance
EVPN: Ethernet VPN
I-SID: Service Instance Identifier (24 bits and global within a
PBB network; see [RFC7080]).
MAC: Media Access Control
PBB: Provider Backbone Bridge
PBB-EVPN: Provider Backbone Bridge EVPN
PE: Provider Edge
VPWS: Virtual Private Wire Service
Single-Active (SA) Redundancy Mode: When only a single PE, among a
group of PEs attached to an Ethernet Segment, ES, is allowed to forward
traffic to/from that Ethernet Segment, ES, the Ethernet
Segment ES is defined as operating in
Single-Active redundancy mode.
All-Active (AA) Redundancy Mode: When all PEs attached to an
Ethernet Segment ES are
allowed to forward traffic to/from that Ethernet Segment, ES, the Ethernet Segment ES is
defined as operating in All-Active redundancy mode.
3. Requirements
This section describes the requirements specific to vES for EVPN and
PBB-EVPN solutions. These requirements are in addition to the ones
described in [RFC8214], [RFC7432], and [RFC7623].
3.1. Single-Homed and Multi-Homed Multihomed vES
A PE device MUST support the following types of vESes:
(R1a) The PE MUST handle single-homed vESes on a single physical
port, such as a single ENNI.
(R1b) The PE MUST support a combination of single-homed vESes and
Single-Active multi-homed multihomed vESes simultaneously on a single
physical port, such as a single ENNI. Throughout this
document, Single-Active multi-homed multihomed vESes will be referred to
as "Single-Active vESes".
(R1c) The PE MAY support All-Active multi-homed multihomed vESes on a single
physical port. Throughout this document, All-Active multi-
homed
multihomed vESes will be referred to as "All-Active vESes".
(R1d) The PE MAY support a combination of All-Active vESes along
with other types of vESes on a single physical port.
(R1e) A multi-homed multihomed vES, whether Single-Active or All-Active, can
span across two or more ENNIs on any two or more PEs.
3.2. Local Switching
Many vESes of different types can be aggregated on a single physical
port on a PE device and some of these vESes can belong to the same
service instance (e.g., EVI). This translates into the need for
supporting local switching among the vESes for the same service
instance on the same physical port (e.g., ENNI) of the PE.
(R3a)
(R2a) A PE device that supports the vES function MUST support local
switching among different vESes associated with the same
service instance on a single physical port. For instance, in
Figure 1, PE1 must support local switching between CE11 and
CE12, which are mapped to two single-homed vESes on ENNI1. In
the case of Single-Active vESes, the local switching is
performed among active EVCs associated with the same service
instance on the same ENNI.
3.3. EVC Service Types
A physical port, such as an ENNI of a PE device, can aggregate
numerous EVCs, each associated with a vES. An EVC may carry one or
more VLANs. Typically, an EVC carries a single VLAN and is therefore
associated with a single broadcast domain. However, there are no
restrictions preventing an EVC from carrying multiple VLANs.
(R4a)
(R3a) An EVC can be associated with a single broadcast domain, such
as in a VLAN-based service or a VLAN bundle service.
(R4b)
(R3b) An EVC MAY be associated with several broadcast domains, such
as in a VLAN-aware bundle service.
Similarly, a PE can aggregate multiple LSPs and PWs. In the case of
individual PWs per vES, a PW is typically associated with a single
broadcast domain, although there are no restrictions preventing a PW
from carrying multiple VLANs if the PW is configured in Raw mode.
(R4c)
(R3c) A PW can be associated with a single broadcast domain, such as
in a VLAN-based service or a VLAN bundle service.
(R4d)
(R3d) A PW MAY be associated with several broadcast domains, such as
in a VLAN-aware bundle service.
3.4. Designated Forwarder (DF) Election
Section 8.5 of [RFC7432] specifies the default procedure for DF
election in EVPN, which is also applied in [RFC7623] and [RFC8214].
[RFC8584] elaborates on additional procedures for DF election in
EVPN. These DF election procedures are performed at the granularity
of (ESI, Ethernet Tag). In the context of a vES, the same EVPN
default procedure for DF election is applicable but at the
granularity of (vESI, Ethernet Tag). In this context, the Ethernet
Tag is represented by an I-SID in PBB-EVPN and by a VLAN ID (VID) in
EVPN. As described in [RFC7432], this default procedure for DF
election at the granularity of (vESI, Ethernet Tag) is also known as
"service carving." The goal of service carving is to evenly
distribute the DFs for different vESes among various PEs, thereby
ensuring an even distribution of traffic across the PEs. The
following requirements are applicable to the DF election of vESes for
EVPN and PBB-EVPN.
(R5a)
(R4a) A PE that supports vES function MUST support a vES with m EVCs
among n ENNIs belonging to p PEs in any arbitrary order, where
n >= p >= m >=2. For example, if there is a vES with 2 EVCs
and there are 5 ENNIs on 5 PEs (PE1 through PE5), then vES can
be dual-homed to PE2 and PE4, and the DF election must be
performed between PE2 and PE4.
(R5b)
(R4b) Each vES MUST be identified by its own virtual ESI (vESI).
3.5. EVC Monitoring
To detect the failure of an individual EVC and subsequently perform
DF election for its associated vES as a result of this failure, each
EVC should be monitored independently.
(R6a)
(R5a) Each EVC SHOULD be independently monitored for its operational
health.
(R6b)
(R5b) A failure in a single EVC, among many aggregated on a single
physical port or ENNI, MUST trigger a DF election for its
associated vES.
3.6. Failure and Recovery
(R7a)
(R6a) Failure and failure recovery of an EVC for a single-homed vES
SHALL NOT impact any other EVCs within its service instance or
any other service instances. In other words, for PBB-EVPN, it
SHALL NOT trigger any MAC flushing within both its own I-SID
and other I-SIDs.
(R7b)
(R6b) In case of All-Active vES, failure and failure recovery of an
EVC for that vES SHALL NOT impact any other EVCs within its
service instance or any other service instances. In other
words, for PBB-EVPN, it SHALL NOT trigger any MAC flushing
within both its own I-SID and other I-SIDs.
(R7c)
(R6c) Failure and failure recovery of an EVC for a Single-Active vES
SHALL impact only its own service instance. In other words,
for PBB-EVPN, MAC flushing SHALL be limited to the associated
I-SID only and SHALL NOT impact any other I-SIDs.
(R7d)
(R6d) Failure and failure recovery of an EVC for a Single-Active vES
MUST only impact C-MACs associated with a multi-homed multihomed device/
network for that service instance. In other words, MAC
flushing MUST be limited to a single service instance (I-SID
in the case of PBB-EVPN) and only C-MACs for a Single-Active
multi-homed
multihomed device/network.
3.7. Fast Convergence
Since many EVCs (and their associated vESes) are aggregated via a
single physical port (e.g., ENNI), when there is a failure of that
physical port, it impacts many vESes and equally triggers many ES
route withdrawals. Formulating, sending, receiving, and processing
such large numbers of BGP messages can introduce delay in DF election
and convergence time. As such, it is highly desirable to have a
mass-withdraw mechanism similar to the one in [RFC7432] for
withdrawing many Ethernet A-D per ES routes.
(R8a)
(R7a) There SHOULD be a mechanism equivalent to EVPN mass withdraw
such that upon an ENNI failure, only a single BGP message to
the PEs is needed to trigger DF election for all impacted
vESes associated with that ENNI.
4. Solution Overview
The solutions described in [RFC7432] and [RFC7623] are leveraged as
is, with the modification that the ESI assignment is performed for an
EVC or a group of EVCs or LSPs/PWs instead of a link or a group of
physical links. In other words, the ESI is associated with a vES
(hereby referred to as the "vESI").
In the EVPN solution, the overall procedures remain consistent, with
the primary difference being the handling of physical port failures
that can affect multiple vESes. Sections 5.1 and 5.3 describe the
procedures for managing physical port or link failures in the context
of EVPN. In a typical multi-homed multihomed setup, MAC addresses learned behind
a vES are advertised using the ESI associated with the vES (i.e., the
vESI). EVPN aliasing and mass-withdraw operations are conducted with
respect to the vES identifier. Specifically, the Ethernet A-D routes
for these operations are advertised using the vESI instead of the
ESI.
For the PBB-EVPN solution, the main change is with respect to the
B-MAC address assignment, which is performed in a similar way to what
is described in Section 7.2.1.1 6.2.1.1 of [RFC7623], with the following
refinements:
* One shared B-MAC address SHOULD be used per PE for the single-
homed vESes. In other words, a single B-MAC is shared for all
single-homed vESes on that PE.
* One shared B-MAC address SHOULD be used per PE, per physical port
(e.g., ENNI) for the Single-Active vESes. In other words, a
single B-MAC is shared for all Single-Active vESes that share the
same ENNI.
* One shared B-MAC address MAY be used for all Single-Active vESes
on that PE.
* One B-MAC address SHOULD be used per set of EVCs representing an
All-Active vES. In other words, a single B-MAC address is used
per vES for All-Active scenarios.
* A single B-MAC address MAY also be used per vES, per PE for
Single-Active scenarios.
4.1. EVPN DF Election for vES
The service carving procedures for vESes are almost the same as the
procedures outlined in Section 8.5 of [RFC7432] and in [RFC8584],
except that ES is replaced with vES.
For the sake of clarity and completeness, the default DF election
procedure of [RFC7432] is repeated below with the necessary changes:
1. When a PE discovers the vESI or is configured with the vESI
associated with its attached vES, it advertises an Ethernet
Segment ES route with
the associated ES-Import extended community attribute.
2. The PE then starts a timer (default value = 3 seconds) to allow
the reception of Ethernet Segment ES routes from other PE nodes connected to the
same vES. This timer value MUST be the same across all PEs
connected to the same vES.
3. When the timer expires, each PE builds an ordered list of the IP
addresses of all the PE nodes connected to the vES (including
itself), in increasing numeric value. Each IP address in this
list is extracted from the "Originator Router's IP address" field
of the advertised Ethernet Segment ES route. Every PE is then given an ordinal
indicating its position in the ordered list, starting with 0 as
the ordinal for the PE with the numerically lowest IP address.
The ordinals are used to determine which PE node will be the DF
for a given EVPN instance on the vES using the following rule:
Assuming a redundancy group of N PE nodes, the PE with ordinal i
is the DF for an EVPN instance with an associated Ethernet Tag
value of V when (V mod N) = i. It should be noted that using the
"Originator Router's IP address" field in the
Ethernet Segment ES route to get the
PE IP address needed for the ordered list allows a CE to be multi-homed
multihomed across different ASes, if such need ever arises.
4. The PE that is elected as a DF for a given EVPN instance will
unblock traffic for that EVPN instance. Note that the DF PE
unblocks all traffic in both ingress and egress directions for
Single-Active vESes and unblocks multi-destination in the egress
direction for All-Active multi-homed multihomed vESes. All non-DF PEs block
all traffic in both ingress and egress directions for Single-
Active vESes and block multi-destination traffic in the egress
direction for All-Active vESes.
In case of an EVC failure, the affected PE withdraws its
corresponding Ethernet Segment ES route if there are no more EVCs associated to the
vES in the PE. This will re-trigger the DF election procedure on all
the PEs in the redundancy group. For PE node failure, or upon PE
commissioning or decommissioning, the PEs re-trigger the DF election
procedure across all affected vESes. In case of a Single-Active, Single-Active
scenario, when a service moves from one PE in the redundancy group to
another PE because of DF re-election, the PE (which ends up being the
elected DF for the service) MUST trigger a MAC address flush
notification towards the associated vES if the
multi-homing multihoming device is
a bridge or the multi-homing multihoming network is an Ethernet bridged network.
For LSP-based and PW-based vES, the non-DF PE SHOULD signal PW-status
'standby' to the Aggregation PE (e.g., AG1 and AG2 in Figure 2), and
a new DF PE MAY send a Label Distribution Protocol (LDP) MAC withdraw
message as a MAC address flush notification. It should be noted that
the PW-status is signaled for the scenarios where there is a one-to-
one mapping between EVI (EVPN instance) and the PW.
4.2. Grouping and Route Coloring for vES
Physical ports (e.g., ENNI) that aggregate many EVCs are 'colored' to
enable the grouping schemes described below.
By default, the MAC address of the corresponding port (e.g., ENNI) is
used to represent the 'color' of the port, and the EVPN Router's MAC
Extended Community defined in [RFC9135] is used to signal this color.
The difference between coloring mechanisms for EVPN and PBB-EVPN is
that the extended community is advertised with the Ethernet A-D per
ES route for EVPN, whereas the extended community is advertised with
the B-MAC route for PBB-EVPN.
The subsequent sections detailing Grouping of Ethernet A-D per ES
routes and Grouping of B-MAC addresses will be essential for
addressing port failure handling, as discussed in Sections 5.3, 5.4,
and 5.5.
4.2.1. EVPN Route Coloring for vES
When a PE discovers the vESI or is configured with the vESI
associated with its attached vES, an Ethernet Segment ES route and Ethernet A-D per ES
route are generated using the vESI identifier.
These Ethernet Segment ES and Ethernet A-D per ES routes specific to each vES are
colored with an attribute representing their association to a
physical port (e.g., ENNI).
The corresponding port 'color' is encoded in the EVPN Router's MAC
Extended Community defined in [RFC9135] and advertised along with the
Ethernet Segment
ES and Ethernet A-D per ES routes for this vES. The color (which is
the MAC address of the port) MUST be unique.
The PE also constructs a special Grouping Ethernet A-D per ES route
that represents all the vESes associated with the port (e.g., ENNI).
The corresponding port 'color' is encoded in the ESI field. For this
encoding, Type 3 ESI (Section 5 of [RFC7432]) is used with the MAC
field set to the color (MAC address) of the port and the 3-octet
local discriminator field set to 0xFFFFFF.
The ESI label extended community (Section 7.5 of [RFC7432]) is not
relevant to Grouping Ethernet A-D per ES route. The label value is
not used for encapsulating Broadcast, Unknown Unicast, and Multicast
(BUM) packets for any split-horizon function. The ESI label extended
community MUST NOT be added to Grouping Ethernet A-D per ES route and
MUST be ignored on receiving the PE.
The Grouping Ethernet A-D per ES route is advertised with a list of
Route Targets corresponding to the affected service instances. If
the number of associated Route Targets exceeds the capacity of a
single route, multiple Grouping Ethernet A-D per ES routes are
advertised accordingly as specified in Section 8.2 of [RFC7432].
4.2.2. PBB-EVPN Route Coloring for vES
In PBB-EVPN, particularly when there are large numbers of service
instances (i.e., I-SIDs) associated with each EVC, the PE device MAY
assign a color attribute to each vES B-MAC route, indicating their
association with a physical port (e.g., an ENNI).
The corresponding port 'color' is encoded in the EVPN Router's MAC
Extended Community defined in [RFC9135] and advertised along with the
B-MAC for this vES in PBB-EVPN.
The PE MAY also construct a special Grouping B-MAC route that
represents all the vESes associated with the port (e.g., ENNI). The
corresponding port 'color' is encoded directly into this special
Grouping B-MAC route.
5. Failure Handling and Recovery
There are several failure scenarios to consider such as:
A: CE uplink port failure
B: Ethernet Access Network failure
C: PE access-facing port or link failure
D: PE node failure
E: PE isolation from IP/MPLS network
The solutions specified in [RFC7432], [RFC7623], and [RFC8214]
provide protection against failures as described in these respective
references. In the context of these solutions, the presence of vESes
introduces an additional failure scenario beyond those already
considered, specifically the failure of individual EVCs. Addressing
vES failure scenarios necessitates the independent monitoring of EVCs
or PWs. Upon detection of failure or service restoration,
appropriate DF election and failure recovery mechanisms must be
executed.
[RFC7023] is used for monitoring EVCs, and upon failure detection of
a given EVC, the DF election procedure per Section 4.1 is executed.
For PBB-EVPN, some extensions are needed to handle the failure and
recovery procedures of [RFC7623] to meet the above requirements.
These extensions are described in the next section.
[RFC4377] and [RFC6310] are used for monitoring the status of LSPs
and/or PWs associated to vES.
B D
|| ||
\/ \/
+-----+
+-----+ | | +---+
| CE1 |EVC2--0=====0--ENNI1| | +-------+
+-----+ | =0--ENNI1|PE1|---| | +---+ +---+
Cust. A | / | | | |IP/MPLS|--|PE3|--|CE4|
+-----+ | / | +---+ |Network| | | +---+
| |EVC2--0== | | | +---+
| CE2 | | | +---+ | |
| |EVC3--0=====0--ENNI2|PE2|---| |
+-----+ | | | | +-------+
+-----+ +---+
/\ /\ /\
|| || ||
A C E
Figure 3: Failure Scenarios A, B, C, D, and E
5.1. EVC Failure Handling for Single-Active vES in EVPN
In [RFC7432], when a DF PE connected to a Single-Active multi-homed
Ethernet Segment multihomed ES
loses connectivity to the segment, due to link or port failure, it
signals the remote PEs to invalidate all MAC addresses associated
with that Ethernet Segment. ES. This is done by means of a mass-withdraw message, by
withdrawing the Ethernet A-D per ES route. It should be noted that
for dual-homing use cases where there is only a single backup path,
MAC invalidating can be avoided by the remote PEs as they can update
their next hop associated with the affected MAC entries to the backup
path per the procedure described in Section 8.2 of [RFC7432].
In case of an EVC failure that impacts a single vES, this same EVPN
procedure is used. In this case, the mass withdraw is conveyed by
withdrawing the Ethernet A-D per vES route carrying the vESI
representing the failed EVC. Upon receiving this message, the remote
PEs perform the same procedures outlined in Section 8.2 of [RFC7432].
5.2. EVC Failure Handling for a Single-Active vES in PBB-EVPN
In [RFC7432], when a PE connected to a Single-Active Ethernet Segment ES loses
connectivity to the segment, due to link or port failure, it signals
the remote PE to flush all C-MAC addresses associated with that Ethernet Segment. ES.
This is done by updating the advertised B-MAC route's MAC Mobility Extended Community.
extended community.
In case of an EVC failure that impacts a single vES, if the above
PBB-EVPN procedure is used, it results in excessive C-MAC flushing
because a single physical port can support a large number of EVCs
(and their associated vESes); therefore, updating the advertised
B-MAC corresponding to the physical port, with MAC Mobility Extended
Community, extended
community, will result in flushing C-MAC addresses not just for the
impacted EVC but for all other EVCs on that port.
To reduce the scope of C-MAC flushing to only the impacted service
instances (the service instance(s) impacted by the EVC failure), the
PBB-EVPN C-MAC flushing needs to be adapted on a per-service-instance
basis (i.e., per I-SID). [RFC9541] introduces a B-MAC/I-SID route
where the existing PBB-EVPN B-MAC route is modified to carry an I-SID
I-SID, instead of a NULL value, in the "Ethernet Tag ID" field instead of NULL value. field. To
the receiving PE, this field indicates flushing all C-MAC addresses
associated with that I-SID for that B-MAC. This C-MAC flushing
mechanism per I-SID SHOULD be used in case of an EVC failure
impacting a vES. Since an EVC typically maps to a single broadcast
domain and thus a single service instance, the affected PE only needs
to advertise a single B-MAC/I-SID route. However, if the failed EVC
carries multiple VLANs each with its own broadcast domain, then the
affected PE needs to advertise multiple B-MAC/I-SID routes -- routes, i.e., one
route for each VLAN (broadcast domain) -- i.e., domain), meaning one route for each
I-SID. Each B-MAC/I-SID route basically instructs the remote PEs to
perform flushing for C-MACs corresponding to the advertised B-MAC
only for the advertised I-SID.
The C-MAC flushing based on a B-MAC/I-SID route works fine when there
are only a few VLANs (e.g., I-SIDs) per EVC. However, if the number
of I-SIDs associated with a failed EVC is large, then it is
RECOMMENDED to assign a B-MAC per vES, and upon EVC failure, the
affected PE simply withdraws this B-MAC message to other PEs.
5.3. Port Failure Handling for Single-Active vESes in EVPN
When many EVCs are aggregated via a single physical port on a PE,
where each EVC corresponds to a vES, then the port failure impacts
all the associated EVCs and their corresponding vESes. If the number
of EVCs corresponding to the Single-Active vESes for that physical
port is in the thousands, then thousands of service instances are
impacted. Therefore, the propagation of failure in BGP needs to
address all these impacted service instances. In order to achieve
this, the following extensions are added to the baseline EVPN
mechanism:
1. The PE MAY color each Ethernet A-D per ES route for a given vES,
as described in Section 4.2.1. The PE SHOULD use the MAC
physical port by default. The receiving PEs take note of this
color and create a list of vESes for this color.
2. The PE MAY advertise a special Grouping Ethernet A-D per ES route
for that color, which represents all the vESes associated with
the port.
3. Upon a port failure (e.g., an ENNI failure), the PE MAY send a
mass-withdraw message by withdrawing the Grouping Ethernet A-D
per ES route.
4. When this message is received, the remote PE MAY detect the
special vES mass-withdraw message by identifying the Grouping
Ethernet A-D per ES route. The remote PEs MAY then access the
list created in (1) of the vESes created per item 1 for the specified color and
locally initiate MAC address invalidating procedures for each of
the vESes in the list.
In scenarios where a logical ENNI is used, the above procedure
equally applies. The logical ENNI is represented by a Grouping
Ethernet A-D per ES route where the Type 3 ESI and the 6 bytes used
in the ENNI's ESI MAC address field are used as a color for the vESes
as described above and in Section 4.2.1.
5.4. Port Failure Handling for Single-Active vESes in PBB-EVPN
When many EVCs are aggregated via a single physical port on a PE,
where each EVC corresponds to a vES, then the port failure impacts
all the associated EVCs and their corresponding vESes. If the number
of EVCs corresponding to the Single-Active vESes for that physical
port is in the thousands, then thousands of service instances
(I-SIDs) are impacted. In such failure scenarios, the following two
MAC flushing mechanisms per [RFC7623] can be performed.
1. If the MAC address of the physical port is used for PBB
encapsulation as B-MAC SA, then upon the port failure, the PE
MUST use the EVPN MAC route withdrawal message to signal the
flush.
2. If the PE's shared MAC address is used for PBB encapsulation as
B-MAC SA, then upon the port failure, the PE MUST re-advertise
this MAC route with the MAC Mobility Extended Community extended community to signal
the flush.
The first method is recommended because it reduces the scope of
flushing the most.
As noted above, the advertisement of the extended community along
with the B-MAC route for coloring purposes is optional and only
recommended when there are many vESes per physical port and each vES
is associated with a very large number of service instances (i.e., a
large number of I-SIDs).
If there are large numbers of service instances (i.e., I-SIDs)
associated with each EVC, and if there is a B-MAC assigned per vES as
recommended in the above section, then in order to handle port
failure efficiently, the following extensions are added to the
baseline PBB-EVPN mechanism:
1. Each vES MAY be colored with a MAC address representing the
physical port like the coloring mechanism for EVPN. In other
words, each B-MAC representing a vES is advertised with the
'color' of the physical port per Section 4.2.2. The receiving
PEs take note of this color being advertised along with the B-MAC
route, and for each such color, they create a list of vESes
associated with this color.
2. The PE MAY advertise a special Grouping B-MAC route for that
color (consisting of a port MAC address by default), which
represents all the vESes associated with the port.
3. Upon a port failure (e.g., ENNI failure), the PE MAY send a mass-
withdraw message by withdrawing the Grouping B-MAC route.
4. When this message is received, the remote PE MAY detect the
special vES mass-withdraw message by identifying the Grouping
B-MAC route. The remote PEs MAY then access the list created in
(1) above for the specified color and flush all C-MACs associated
with the failed physical port.
5.5. Fast Convergence in EVPN and PBB-EVPN
As described above, when many EVCs are aggregated via a physical port
on a PE, and where each EVC corresponds to a vES, the port failure
impacts all the associated EVCs and their corresponding vESes. Two
actions must be taken as the result of such a port failure:
* For EVPN, initiate the mass-withdraw procedure for all vESes
associated with the failed port to invalidate MACs and for PBB-
EVPN to flush all C-MACs associated with the failed port across
all vESes and the impacted I-SIDs
* Use DF election for all impacted vESes associated with the failed
port
Section 5.3 already describes how to perform a mass withdraw for all
affected vESes and invalidate MACs using a single BGP withdrawal of
the Grouping Ethernet A-D per ES route. Section 5.4 describes how to
only flush C-MAC addresses associated with the failed physical port
(e.g., optimum C-MAC flushing) as well as, optionally, the withdrawal
of a Grouping B-MAC route.
This section describes how to perform DF election in the most optimal
way, e.g., by triggering DF election for all impacted vESes (which
can be very large) among the participating PEs via a single BGP
message as opposed to sending a large number of BGP messages (one per
vES). This section assumes that the MAC flushing mechanism described
in Section 5.4 and route coloring are used.
+-----+
+----+ | | +---+
| CE1|AC1--0=====0--ENNI1| | +-------+
| |AC2--0 | |PE1|--| |
+----+ |\ ==0--ENNI2| | | |
| \/ | +---+ | |
| /\ | |IP/MPLS|
+----+ |/ \ | +---+ |Network| +---+ +---+
| CE2|AC4--0 =0--ENNI3| | | |---|PE4|--|CE4|
| |AC4--0=====0--ENNI3|PE2|--| | +---+ +---+
+----+ | ====0--ENNI3| | | |
|/ | +---+ | |
0 | | |
+----+ /| | +---+ | |
| CE3|AC5- | | |PE3|--| |
| |AC6--0=====0--ENNI4| | +-------+
+----+ | | +---+
+-----+
Figure 4: Fast Convergence Upon ENNI Failure
As discussed in Section 4.2, it is highly desirable to have a mass-
withdraw mechanism similar to the one in [RFC7432]. Although such an
optimization is desirable, it is OPTIONAL. If the optimization is
implemented, the following procedures are used:
1. When a vES is configured, the PE advertises the Ethernet Segment ES route for this
vES with a color that corresponds to the associated physical
port.
2. All receiving PEs within the redundancy group record this color
and compile a list of vESes associated with it.
3. Additionally, the PE advertises a Grouping Ethernet A-D per ES
route for EVPN, and a Grouping B-MAC route for PBB-EVPN, which
corresponds to the color and vES grouping.
4. In the event of a port failure, such as an ENNI failure, the PE
withdraws the previously advertised Grouping Ethernet A-D per ES
route or Grouping B-MAC route associated with the failed port.
The PE should prioritize sending these Grouping route withdrawal
messages over the withdrawal of individual vES routes affected by
the failure. For instance, as depicted in Figure 4, when the
physical port associated with ENNI3 fails on PE2, it withdraws
the previously advertised Grouping Ethernet A-D per ES route.
Upon receiving this withdrawal message, other multi-homing multihoming PEs
(such as PE1 and PE3) recognize that the vESes associated with
CE1 and CE3 are impacted, based on the associated color, and thus
initiate the DF election procedure for these vESes. Furthermore,
upon receiving this withdrawal message, remote PEs (such as PE4)
initiate the failover procedure for the vESes associated with CE1
and CE3 and switch to the other PE for each vES redundancy group.
5. On reception of Grouping Ethernet A-D per ES route or Grouping
B-MAC route withdrawal, other PEs in the redundancy group
initiate DF election procedures across all their affected vESes.
6. The PE with the physical port failure (ENNI failure) sends a vES
route withdrawal for every impacted vES. Upon receiving these
messages, the other PEs clear up their BGP tables. It should be
noted that the vES route withdrawal messages are not used for
executing DF election procedures by the receiving PEs when
Grouping Ethernet A-D per ES route or Grouping B-MAC route
withdrawal has been previously received.
6. Security Considerations
All the security considerations in [RFC7432] and [RFC7623] apply
directly to this document because this document leverages the control
and data plane procedures described in those documents.
This document does not introduce any new security considerations
beyond that of [RFC7432] and [RFC7623] because advertisements and the
processing of Ethernet Segment ES routes for vES in this document follow that of
physical ES in those RFCs.
7. IANA Considerations
This document has no IANA actions.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[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>.
[RFC7623] Sajassi, A., Ed., Salam, S., Bitar, N., Isaac, A., and W.
Henderickx, "Provider Backbone Bridging Combined with
Ethernet VPN (PBB-EVPN)", RFC 7623, DOI 10.17487/RFC7623,
September 2015, <https://www.rfc-editor.org/info/rfc7623>.
[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>.
[RFC8365] Sajassi, A., Ed., Drake, J., Ed., Bitar, N., Shekhar, R.,
Uttaro, J., and W. Henderickx, "A Network Virtualization
Overlay Solution Using Ethernet VPN (EVPN)", RFC 8365,
DOI 10.17487/RFC8365, March 2018,
<https://www.rfc-editor.org/info/rfc8365>.
[RFC9135] Sajassi, A., Salam, S., Thoria, S., Drake, J., and J.
Rabadan, "Integrated Routing and Bridging in Ethernet VPN
(EVPN)", RFC 9135, DOI 10.17487/RFC9135, October 2021,
<https://www.rfc-editor.org/info/rfc9135>.
[RFC9541] Rabadan, J., Ed., Sathappan, S., Nagaraj, K., Miyake, M.,
and T. Matsuda, "Flush Mechanism for Customer MAC
Addresses Based on Service Instance Identifier (I-SID) in
Provider Backbone Bridging EVPN (PBB-EVPN)", RFC 9541,
DOI 10.17487/RFC9541, March 2024,
<https://www.rfc-editor.org/info/rfc9541>.
8.2. Informative References
[MEF63] Metro Ethernet Forum, "Subscriber Ethernet Services
Definitions", MEF Standard, MEF 6.3, November 2019. 2019,
<https://www.mef.net/resources/mef-6-3-subscriber-
ethernet-service-definitions>.
[RFC4377] Nadeau, T., Morrow, M., Swallow, G., Allan, D., and S.
Matsushima, "Operations and Management (OAM) Requirements
for Multi-Protocol Label Switched (MPLS) Networks",
RFC 4377, DOI 10.17487/RFC4377, February 2006,
<https://www.rfc-editor.org/info/rfc4377>.
[RFC6310] Aissaoui, M., Busschbach, P., Martini, L., Morrow, M.,
Nadeau, T., and Y. Stein, "Pseudowire (PW) Operations,
Administration, and Maintenance (OAM) Message Mapping",
RFC 6310, DOI 10.17487/RFC6310, July 2011,
<https://www.rfc-editor.org/info/rfc6310>.
[RFC7023] Mohan, D., Ed., Bitar, N., Ed., Sajassi, A., Ed., DeLord,
S., Niger, P., and R. Qiu, "MPLS and Ethernet Operations,
Administration, and Maintenance (OAM) Interworking",
RFC 7023, DOI 10.17487/RFC7023, October 2013,
<https://www.rfc-editor.org/info/rfc7023>.
[RFC7080] Sajassi, A., Salam, S., Bitar, N., and F. Balus, "Virtual
Private LAN Service (VPLS) Interoperability with Provider
Backbone Bridges", RFC 7080, DOI 10.17487/RFC7080,
December 2013, <https://www.rfc-editor.org/info/rfc7080>.
[RFC7209] Sajassi, A., Aggarwal, R., Uttaro, J., Bitar, N.,
Henderickx, W., and A. Isaac, "Requirements for Ethernet
VPN (EVPN)", RFC 7209, DOI 10.17487/RFC7209, May 2014,
<https://www.rfc-editor.org/info/rfc7209>.
[RFC8584] Rabadan, J., Ed., Mohanty, S., Ed., Sajassi, A., Drake,
J., Nagaraj, K., and S. Sathappan, "Framework for Ethernet
VPN Designated Forwarder Election Extensibility",
RFC 8584, DOI 10.17487/RFC8584, April 2019,
<https://www.rfc-editor.org/info/rfc8584>.
[RFC9252] Dawra, G., Ed., Talaulikar, K., Ed., Raszuk, R., Decraene,
B., Zhuang, S., and J. Rabadan, "BGP Overlay Services
Based on Segment Routing over IPv6 (SRv6)", RFC 9252,
DOI 10.17487/RFC9252, July 2022,
<https://www.rfc-editor.org/info/rfc9252>.
Acknowledgements
The authors would like to thank Mei Zhang, Jose Liste, and Luc André
Burdet for their reviews of this document and their feedback.
Authors' Addresses
Ali Sajassi
Cisco Systems
Email: sajassi@cisco.com
Patrice Brissette
Cisco Systems
Email: pbrisset@cisco.com
Rick Schell
Verizon
Email: richard.schell@verizon.com
John E Drake
Juniper
Email: jdrake@juniper.net
Jorge Rabadan
Nokia
Email: jorge.rabadan@nokia.com