Internet Working Group A. Sajassi
Internet Draft P. Brissette
Category: Standards Track Cisco
R. Schell
Verizon
J. Drake
Juniper
J. Rabadan
Nokia
Expires: July 09, 2019 January 09, 2019
EVPN Virtual Ethernet Segment
draft-ietf-bess-evpn-virtual-eth-segment-03
Abstract
EVPN and PBB-EVPN introduce a family of solutions for multipoint
Ethernet services over MPLS/IP network with many advanced features
among which their multi-homing capabilities. These solutions define
two types of multi-homing for an Ethernet Segment (ES): 1) Single-
Active and 2) All-Active, where an Ethernet Segment is defined as a
set of links between the multi-homed device/network and the set of PE
devices that they are connected to.
Some Service Providers want to extend the concept of the physical
links in an ES to Ethernet Virtual Circuits (EVCs) where many of such
EVCs can be aggregated on a single physical External Network-to-
Network Interface (ENNI). An ES that consists of a set of EVCs
instead of physical links is referred to as a virtual ES (vES). This
draft describes the requirements and the extensions needed to support
vES in EVPN and PBB-EVPN.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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Copyright and License Notice
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Conventions
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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Virtual Ethernet Segments in Access Ethernet Networks . . . 4
1.2 Virtual Ethernet Segments in Access MPLS Networks . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1. Single-Homed & Multi-Homed Virtual Ethernet Segments . . . 8
3.2. Scalability . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3. Local Switching . . . . . . . . . . . . . . . . . . . . . . 9
3.4. EVC Service Types . . . . . . . . . . . . . . . . . . . . . 9
3.5. Designated Forwarder (DF) Election . . . . . . . . . . . . 10
3.6. OAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.7. Failure & Recovery . . . . . . . . . . . . . . . . . . . . 11
3.8. Fast Convergence . . . . . . . . . . . . . . . . . . . . . 11
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4. Solution Overview . . . . . . . . . . . . . . . . . . . . . . . 11
4.1. EVPN DF Election for vES . . . . . . . . . . . . . . . . . 13
5. Failure Handling & Recovery . . . . . . . . . . . . . . . . . . 14
5.1. Failure Handling for Single-Active vES in EVPN . . . . . . 15
5.2. EVC Failure Handling for Single-Active vES in PBB-EVPN . . 16
5.3. Port Failure Handling for Single-Active vES's in EVPN . . . 17
5.4. Port Failure Handling for Single-Active vES's in PBB-EVPN . 18
5.5. Fast Convergence in PBB-EVPN . . . . . . . . . . . . . . . 18
6. BGP Encoding . . . . . . . . . . . . . . . . . . . . . . . . . 20
6.1. I-SID Extended Community . . . . . . . . . . . . . . . . . 21
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21
8. Security Considerations . . . . . . . . . . . . . . . . . . . . 21
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 21
10. Intellectual Property Considerations . . . . . . . . . . . . . 22
11. Normative References . . . . . . . . . . . . . . . . . . . . . 22
12. Informative References . . . . . . . . . . . . . . . . . . . . 22
13. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 22
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1. Introduction
[RFC7432] and [RFC7623] introduce a family of solutions for
multipoint Ethernet services over MPLS/IP network with many advanced
features among which their multi-homing capabilities. These solutions
define two types of multi-homing for an Ethernet Segment (ES): 1)
Single-Active and 2) All-Active, where an Ethernet Segment is defined
as a set of links between the multi-homed device/network and the set
of PE devices that they are connected to.
This document extends the Ethernet Segment concept so that an ES can
be associated to a set of EVCs (e.g., VLANs) or other objects such as
MPLS Label Switch Paths (LSPs) or Pseudowires (PWs).
1.1 Virtual Ethernet Segments in Access Ethernet Networks
Some Service Providers (SPs) want to extend the concept of the
physical links in an ES to Ethernet Virtual Circuits (EVCs) where
many of such EVCs (e.g., VLANs) can be aggregated on a single
physical External Network-to-Network Interface (ENNI). An ES that
consists of a set of EVCs instead of physical links is referred to as
a virtual ES (vES). Figure below depicts two PE devices (PE1 and PE2)
each with an ENNI where a number of vES's are aggregated on - each of
which through its associated EVC.
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Carrier
Ethernet
+-----+ Network
| CE11|EVC1 +---------+ <---- EVPN Network ----->
+-----+ \ | | +---+
Cust. A \-0=========0--ENNI1| |
+-----+ | | ENNI1| | +-------+ +---+
| CE12|EVC2--0=========0--ENNI1|PE1|---| | | |
+-----+ | | ENNI1| | | |---|PE3|-
| ==0--ENNI1| | |IP/MPLS| | | \ +---+
+-----+ | / | +---+ |Network| +---+ \-| |
| CE22|EVC3--0==== / | | | |CE4|
+-----+ | X | | | +---+ | |
| / \ | +---+ | | | | /-| |
+-----+ -0=== ===0--ENNI2| | | |---|PE4|-/ +---+
| CE3 |EVC4/ | | ENNI2|PE2|---| | | |
| |EVC5--0=========0--ENNI2| | +-------+ +---+
+-----+ | | +---+
Cust. C +---------+ /\
/\ ||
|| ENNI
EVCs Interface
<--------802.1Q----------> <-802.1Q->
Figure 1: DHD/DHN (both SA/AA) and SH on same ENNI
E-NNIs are commonly used to reach off-network / out-of-franchise
customer sites via independent Ethernet access networks or third-
party Ethernet Access Providers (EAP) (see Figure 1). E-NNIs can
aggregate traffic from hundreds to thousands of vES's; where, each
vES is represented by its associated EVC on that ENNI. As a result,
ENNIs and their associated EVCs are a key element of SP off-networks
that are carefully designed and closely monitored.
In order to meet customer's Service Level Agreements (SLA), SPs build
redundancy via multiple EVPN PEs and across multiple ENNIs (as shown
in Figure 1) where a given vES can be multi-homed to two or more EVPN
PE devices (on two or more ENNIs) via their associated EVCs. Just
like physical ES's in [RFC7432] and [RFC7623] solutions, these vES's
can be single-homed or multi-homed ES's and when multi-homed, then
can operate in either Single-Active or All-Active redundancy modes.
In a typical SP off-network scenario, an ENNI can be associated with
several thousands of single-homed vES's, several hundreds of Single-
Active vES's and it may also be associated with tens or hundreds of
All-Active vES's.
1.2 Virtual Ethernet Segments in Access MPLS Networks
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Other Service Providers (SPs) want to extend the concept of the
physical links in an ES to individual Pseudowires (PWs) or to MPLS
Label Switched Paths (LSPs) in Access MPLS networks. Figure 2
illustrates this concept.
MPLS Aggregation
Network
+-----+ +----------------+ <---- EVPN Network ----->
| CE11|EVC1 | |
+-----+ \+AG1--+ PW1 +-----+
Cust. A -0----|===========| |
+-----+ | ---+===========| | +-------+ +---+
| CE12|EVC2-0/ | PW2 /\ | PE1 +---+ | | |
+-----+ ++---+ ==||=| | | +---+PE3+-
| //=||=| | |IP/MPLS| | | \ +---+
| // \/ ++----+ |Network| +---+ \-+ |
+-----+EVC3 | PW3// LSP1 | | | |CE4|
| CE13| +AG2--+===/PW4 | | | +---+ | |
+-----+ 0 |=== /\ ++----+ | | | | /-+ |
0 |==PW5===||=| | | +---+PE4+-/ +---+
+-----+ /++---+==PW6===||=| PE2 +---+ | | |
| CE14|EVC4 | \/ | | +-------+ +---+
+-----+ | LSP2+-----+
Cust. C +----------------+
/\
||
EVCs
<--802.1Q---><------MPLS-------> <-802.1Q->
Figure 2: DHN and SH on Access MPLS networks
In some cases, Service Providers use Access MPLS Networks that belong
to separate administrative entities or third parties as a way to get
access to the their own IP/MPLS network infrastructure. This is the
case illustrated in Figure 2.
In such scenarios, a virtual ES (vES) is defined as a set of
individual PWs if they cannot be aggregated into a common LSP. If the
aggregation of PWs is possible, the vES can be associated to an LSP
in a given PE. In the example of 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 a separate VPWS instance on AG2
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that gets connected to an EVI on PE1 and PE2 via PW4 and PW6,
respectively. Since the PWs for the two VPWS instances can be
aggregated into the same LSPs going to the EVPN network, a common
virtual ES can be defined for LSP1 and LSP2. This vES will be shared
by two separate EVIs in the EVPN network.
In some cases, this aggregation of PWs into common LSPs 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 PW on each PE, i.e. PW3 and PW5 would belong to ES-1,
whereas PW4 and PW6 would be associated to ES-2.
For MPLS/IP access networks where a vES represents a set of PWs or
LSPs, this document extended Single-Active multi-homing procedures of
[RFC7432] and [7623] to vES. The vES extension to All-Active multi-
homing is outside of the scope of this document for MPLS/IP access
networks.
This draft describes requirements and the extensions needed to
support vES in [RFC7432] and [RFC7623]. Section 3 lists the set of
requirements for virtual ES's. Section 4 describes the solution for
[RFC7432], [RFC7623], and [RFC8214] to meet these requirements.
Section 5 describes the failure handling and recovery for Virtual
ES's in [RFC7432] and [RFC7623]. Section 6 covers scalability and
fast convergence required for Virtual ES's in [RFC7432] and
[RFC7623].
2. Terminology
AC: Attachment Circuit
BEB: Backbone Edge Bridge
B-MAC: Backbone MAC Address
CE: Customer Edge
CFM: Connectivity Fault Management
C-MAC: Customer/Client MAC Address
DHD: Dual-homed Device
DHN: Dual-homed Network
ENNI: External Network-Network Interface
ES: Ethernet Segment
ESI: Ethernet-Segment Identifier
EVC: Ethernet Virtual Circuit
EVPN: Ethernet VPN
I-SID: Service Instance Identifier (24 bits and global within a PBB
network see [RFC7080])
LACP: Link Aggregation Control Protocol
PBB: Provider Backbone Bridge
PBB-EVPN: Provider Backbone Bridge EVPN
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PE: Provider Edge
SH: Single-Homed
Single-Active Redundancy Mode (SA): When only a single PE, among a
group of PEs attached to an Ethernet-Segment, is allowed to forward
traffic to/from that Ethernet Segment, then the Ethernet segment is
defined to be operating in Single-Active redundancy mode.
All-Active Redundancy Mode (AA): When all PEs attached to an Ethernet
segment are allowed to forward traffic to/from that Ethernet-Segment,
then the Ethernet segment is defined to be operating in All-Active
redundancy mode.
3. Requirements
This section describes the requirements specific to virtual Ethernet
Segment (vES) for (PBB-)EVPN solutions. These requirements are in
addition to the ones described in [RFC7209], [RFC7432], and
[RFC7623].
3.1. Single-Homed & Multi-Homed Virtual Ethernet Segments
A PE needs to support the following types of vES's:
(R1a) A PE MUST handle single-homed vES's on a single physical port
(e.g., single ENNI)
(R1b) A PE MUST handle a mix of Single-Homed vES's and Single-Active
multi-homed vES's simultaneously on a single physical port (e.g.,
single ENNI). Single-Active multi-homed vES's will be simply referred
to as Single-Active vES's through the rest of this document.
(R1c) A PE MAY handle All-Active multi-homed vES's on a single
physical port. All-Active multi-homed vES's will be simply referred
to as All-Active vES's through the rest of this document.
(R1d) A PE MAY handle a mixed of All-Active vES's along with other
types of vES's on a single physical port
(R1e) A Multi-Homed vES (Single-Active or All-Active) can be spread
across any two or more PEs (on two or more ENNIs)
3.2. Scalability
A single physical port (e.g., ENNI) can be associated with many
vES's. The following requirements give a quantitative measure for
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each vES type.
(R2a) A PE SHOULD handle very large number of Single-Homed vES's on a
single physical port (e.g., thousands of vES's on a single ENNI)
(R2b) A PE SHOULD handle large number of Single-Active vES's on a
single physical port (e.g., hundreds of vES's on a single ENNI)
(R2c) A PE MAY handle large number of All-Active Multi-Homed vES's on
a single physical port (e.g., hundreds of vES's on a single ENNI)
(R2d) A PE SHOULD handle the above scale for a mix of Single-homed
vES's and Single-Active vES's simultaneously on a single physical
port (e.g., single ENNI)
(R4e) A PE MAY handle the above sale for a mixed of All-Active Multi-
Homed vES's along with other types of vES's on a single physical port
3.3. Local Switching
Many vES's of different types can be aggregated on a single physical
port on a PE device and some of these vES can belong to the same
service instance (or customer). This translates into the need for
supporting local switching among the vES's of the same service
instance on the same physical port (e.g., ENNI) of the PE.
(R3a) A PE MUST support local switching among different vES's
belonging to the same service instance (or customer) on a single
physical port. For example, in Figure 1, PE1 MUST support local
switching between CE11 and CE12 (both belonging to customer A) that
are mapped to two Single-homed vES's on ENNI1.
In case of Single-Active vES's, the local switching is performed
among active EVCs belonging to the same service instance on the same
ENNI.
3.4. EVC Service Types
A physical port (e.g., ENNI) of a PE can aggregate many EVCs each of
which is associated with a vES. Furthermore, an EVC may carry one or
more VLANs. Typically, an EVC carries a single VLAN and thus it is
associated with a single broadcast domain. However, there is no
restriction on an EVC to carry more than one VLAN.
(R4a) An EVC can be associated with a single broadcast domain - e.g.,
VLAN-based service or VLAN bundle service
(R4b) An EVC MAY be associated with several broadcast domains - e.g.,
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VLAN-aware bundle service
In the same way, a PE can aggregate many LSPs and PWs. In the case of
individual PWs per vES, typically a PW is associated with a single
broadcast domain, but there is no restriction on the PW to carry more
than one VLAN if the PW is defined as vc-type VLAN.
(R4c) A PW can be associated with a single broadcast domain - e.g.,
VLAN-based service or VLAN bundle service.
(R4d) An PW MAY be associated with several broadcast domains - e.g.,
VLAN-aware bundle service."
3.5. Designated Forwarder (DF) Election
Section 8.5 of [RFC7432] describes the default procedure for DF
election in EVPN which is also used in [RFC7623] and [RFC8214]. This
default DF election procedure is performed at the granularity of
<ESI, Ethernet Tag>. In case of a vES, the same EVPN default
procedure for DF election also applies; however, at the granularity
of <vESI, Ethernet Tag>; where vESI is the virtual Ethernet Segment
Identifier. As in [RFC7432], this default procedure for DF election
at the granularity of <vESI, Ethernet Tag> is also referred to as
"service carving"; where, Ethernet Tag is represented by an I-SID in
PBB-EVPN and by a VLAN ID (VID) in EVPN. With service carving, it is
possible to evenly distribute the DFs for different vES's among
different PEs, thus distributing the traffic among different PEs. The
following list the requirements apply to DF election of vES's for
EVPN.
(R5a) A vES with m EVCs can be distributed among n ENNIs belonging to
p PEs in any arbitrary oder; where n >= p >= m. For example, if there
is an 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) Each vES MUST be identified by its own virtual ESI (vESI)
3.6. OAM
In order to detect the failure of individual EVC and perform DF
election for its associated vES as the result of this failure, each
EVC should be monitored independently.
(R6a) Each EVC SHOULD be monitored for its health independently
(R6b) A single EVC failure (among many aggregated on a single
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physical port/ENNI) MUST trigger DF election for its associated vES.
3.7. Failure & Recovery
(R7a) Failure and failure recovery of an EVC for a Single-homed vES
SHALL NOT impact any other EVCs for its own service instance or any
other service instances. In other words, for PBB-EVPN, it SHALL NOT
trigger any MAC flushing both within its own I-SID as well as other
I-SIDs.
(R7b) In case of All-Active Multi-Homed vES, failure and failure
recovery of an EVC for that vES SHALL NOT impact any other EVCs for
its own service instance or any other service instances. In other
words, for PBB-EVPN, it SHALL NOT trigger any MAC flushing both
within its own I-SID as well as other I-SIDs.
(R7c) Failure & failure recovery of an EVC for a Single-Active vES
SHALL only impact 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) Failure & failure recovery of an EVC for a Single-Active vES
MAY only impact C-MACs associated with MHD/MHNs for that service
instance. In other words, MAC flushing SHOULD be limited to single
service instance (I-SID in the case of PBB-EVPN) and only CMACs for
Single-Active MHD/MHNs.
3.8. Fast Convergence
Since large number of EVCs (and their associated vES's) are
aggregated via a single physical port (e.g., ENNI), then the failure
of that physical port impacts large number of vES's and triggers
large number of ES route withdrawals. Formulating, sending,
receiving, and processing such large number 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 the [RFC7432] for withdrawing large number of Ethernet A-D routes.
(R8a) There SHOULD be a mechanism equivalent to EVPN mass-withdraw
such that upon an ENNI failure, only a single BGP message is needed
to indicate to the remote PEs to trigger DF election for all impacted
vES associated with that ENNI.
4. Solution Overview
The solutions described in [RFC7432] and [RFC7623] are leveraged as
is with one simple modification and that is the ESI assignment is
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performed for a group of EVCs or LSPs/PWs instead of a group of
links. In other words, the ESI is associated with a virtual ES (vES)
and that's why it will be referred to as vESI.
For the EVPN solution, everything basically remains the same except
for the handling of physical port failure where many vES's can be
impacted. Section 5.1 and 5.3 below describe the handling of physical
port/link failure for EVPN. In a typical multi-homed operation, MAC
addresses are learned behind a vES are advertised with the ESI
corresponding to the vES (i.e., vESI). EVPN aliasing and mass-
withdraw operations are performed with respect to vES. In other
words, the Ethernet A-D routes for these operations are advertised
with vESI instead of ESI.
For PBB-EVPN solution, the main change is with respect to the BMAC
address assignment which is performed similar to what is described in
section 7.2.1.1 of [RFC7623] with the following refinements:
- One shared BMAC address is used per PE for the single-homed vES's.
In other words, a single BMAC is shared for all single-homed vES's on
that PE.
- One shared BMAC address should be used per PE per physical port
(e.g., ENNI) for the Single-Active vES's. In other words, a single
BMAC is shared for all Single-Active vES's that shared the same ENNI.
- One shared BMAC address can be used for all Single-Active vES's on
that PE.
- One BMAC address is used per EVC per physical port per PE for each
All-Active multi-homed vES. In other words, a single BMAC address is
used per vES for All-Active multi-homing scenarios.
- A single BMAC address may also be used per vES per PE for Single-
Active multi-homing scenarios.
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BEB +--------------+ BEB
|| | | ||
\/ | | \/
+----+ EVC1 +----+ | | +----+ +----+
| CE1|------| | | | | |---| CE2|
+----+\ | PE1| | IP/MPLS | | PE3| +----+
\ +----+ | Network | +----+
\ | |
EVC2\ +----+ | |
\ | | | |
\| PE2| | |
+----+ | |
/\ +--------------+
||
BEB
<--802.1Q--><---------- PBB-EVPN --------><--802.1Q->
Figure 3: PBB-EVPN Network
4.1. EVPN DF Election for vES
The procedure for service carving for virtual Ethernet Segments is
the same as the one outlined in section 8.5 of [RFC7432] except for
the fact that ES is replaced with vES. For the sake of clarity and
completeness, this procedure is repeated below:
1. When a PE discovers the vESI or is configured with the vESI
associated with its attached vES, it advertises an Ethernet Segment
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 routes from other PE nodes
connected to the same vES. This timer value MUST be 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 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.
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It should be noted that using "Originator Router's IP address" field
in the Ethernet Segment route to get the PE IP address needed for the
ordered list, allows for a CE to be multi-homed 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
vES and unblocks multi-destination in egress direction for All-Active
Multi-homed vES. All non-DF PEs block all traffic in both ingress and
egress directions for Single-Active vES and block multi-destination
traffic in the egress direction for All-Active multi-homed vES.
In the case of an EVC failure, the affected PE withdraws its Ethernet
Segment 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 RG. For PE node failure, or upon PE commissioning or
decommissioning, the PEs re-trigger the DF Election Procedure across
all affected vES's. In case of a Single-Active multi-homing, when a
service moves from one PE in the Redundancy Group to another PE as a
result of DF re-election, the PE, which ends up being the elected DF
for the service, SHOULD trigger a MAC address flush notification
towards the associated vES. This can be done, for e.g. using IEEE
802.1ak MVRP 'new' declaration.
For LSP and PW based vES, the non-DF PE SHOULD signal PW-status
'standby' signaling to the AG PE, and the new DF MAY send an 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/BD and the PW.
5. Failure Handling & Recovery
There are a number of 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
[RFC7432], [RFC7623], and [RFC8214] solutions provide protection
against such failures as described in the corresponding references.
In the presence of virtual Ethernet Segments (vES's) in these
solutions, besides the above failure scenarios, there is one more
scenario to consider and that is EVC failure. This implies that
individual EVCs need to be monitored and upon their failure
detection, appropriate DF election procedures and failure recovery
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mechanism need to be executed.
[ETH-OAM] is used for monitoring EVCs and upon failure detection of a
given EVC, 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] in order to meet the above
requirements. These extensions are describe in the next section.
[MPLS-OAM] and [PW-OAM] 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 4: Failure Scenarios A,B,C,D and E
5.1. Failure Handling for Single-Active vES in EVPN
When a PE connected to a Single-Active multi-homed Ethernet Segment
loses connectivity to the segment, due to link or port failure, it
signals the remote PE to flush all CMAC addresses associated with
that Ethernet Segment. This is done by advertising a mass-withdraw
message using Ethernet A-D per-ES route. To be precise, there is no
MAC flush per-se if there is only one backup PE for a given ES -
i.e., only an update of the forwarding entries per backup-path
procedure in [RFC 7432].
In case of an EVC failure that impacts a single vES, the exact same
EVPN procedure is used. In this case, the message using Ethernet A-D
per ES route carries the vESI representing the vES which is in turn
associated with the failed EVC. The remote PEs upon receiving this
message perform the same procedures outlined in section 8.2 of
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[RFC7432].
5.2. EVC Failure Handling for Single-Active vES in PBB-EVPN
When a PE connected to a Single-Active multi-homed Ethernet Segment
loses connectivity to the segment, due to link or port failure, it
signals the remote PE to flush all CMAC addresses associated with
that Ethernet Segment. This is done by advertising a BMAC route along
with MAC Mobility 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 CMAC flushing
because a single physical port can support large number of EVCs (and
their associated vES's) and thus advertising a BMAC corresponding to
the physical port with MAC mobility Extended community will result in
flushing CMAC addresses not just for the impacted EVC but for all
other EVCs on that port.
In order to reduce the scope of CMAC flushing to only the impacted
service instances (the service instance(s) impacted by the EVC
failure), the BGP flush message is sent along with a list of impacted
I-SID(s) represented by the new EVPN I-SID Extended Community as
defined in section 6. Since typically an EVC maps to a single
broadcast domain and thus a single service instance, the list only
contains a single I-SID. However, if the failed EVC carries multiple
VLANs each with its own broadcast domain, then the list contains
several I-SIDs - one for each broadcast domain. This new BGP flush
message basically instructs the remote PE to perform flushing for
CMACs corresponding to the advertised BMAC only across the advertised
list of I-ISIDs.
The new I-SID Extended Community provides a way to encode upto 24 I-
SIDs in each Extended Community if the impacted I-SIDs are sequential
(the base I-SID value plus the next 23 I-SID values). If the number
of I-SIDs associated with a failed EVC is large or if the affected I-
SIDs are not sequential, then multiple I-SID Extended Communities can
be sent along with the flush message. However, if the number of
affected I-SIDs is very large such that the corresponding I-SID
Extended Communities don't fit in a single BGP attribute, then the
EVC failure can be treated as a port failure and the procedures of
section 5.4 can be exercised (i.e., a single BGP flush message
without the I-SID list can be transmitted). When the BGP flush
message is transmitted without the I-SID list, then it instructs the
receiving PEs to flush CMACs associated with that BMAC across all I-
SIDs.
There can be scenarios (although unlikely) where multiple EVCs within
the same physical port can fail within a short time resulting in the
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PE advertising multiple BGP flush messages each with their own list
of I-SIDs; however, the route reflector receiving these messages will
only send the last flush message. This results in PEs receiving such
flush messages not to properly flush all the affected I-SIDs. In
order to address such scenarios, a timer T1 is started upon an EVC1
failure on the advertising PE. If there is another EVC2 failure
within T1, affected I-SIDs are aggregated for both EVC1 and EVC2 to
be sent along the new flush message. Furthermore when EVC2 failure
occurs, another timer T2 (with the same value as T1) is started to
keep track of the affected I-SIDs for EVC2. Such I-SID aggregation
may result in multiple flushing for the same I-SID(s) on the
receiving PEs. The default value for this timer T is 30 seconds.
The I-SID dependent flushing mechanism described in this section is
backward compatible for the PEs only supporting [RFC7623] such that
the PEs that don't understand the I-SID list (i.e., the new I-SID
Extended Community) simply ignore it and default to flushing all the
I-SIDs for the B-MAC - i.e., the PEs default to per-port flushing
described in section 5.4.
The above BMAC route that is advertised with the MAC Mobility
Extended Community, can either represent the MAC address of the
physical port that the failed EVC is associated with, or it can
represent the MAC address of the PE. In the latter case, this is the
dedicated per-PE MAC address used for all Single-Active vES's on that
PE. The former one performs better than the latter one in terms of
reducing the scope of flushing and thus it is the recommended
approach because only CMAC addresses for the impacted service
instances on the failed EVC are flushed.
5.3. Port Failure Handling for Single-Active vES's in EVPN
When a large number of 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 vES's. If the
number of EVCs corresponding to the Single-Active vES's for that
physical port is in thousands, then thousands of service instances
are impacted. Therefore, the BGP flush message need to be inclusive
of all these impacted service instances. In order to achieve this,
the following extensions are added to the baseline EVPN mechanism:
1) When a PE advertises an Ether-AD per ES route for a given vES, it
colors it with the MAC address of the physical port which is
associated with that vES using EVPN Router's MAC Extended Community
per [EVPN-IRB]. The receiving PEs take note of this color and create
a list of vES's for this color.
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2) Upon a port failure (e.g., ENNI failure), the PE advertise a
special mass-withdraw message with the MAC address of the failed port
(i.e., the color of the port) encoded in the ESI field. For this
encoding, type 3 ESI is used with the MAC field set to the MAC
address of the port and the 3-octet local discriminator field set to
0xFFFFFF. This mass-withdraw route is advertised with a list of Route
Targets corresponding to the impacted service instances. If the
number of Route Targets is more than they can fit into a single
attribute, then a set of Ethernet A-D per ES routes are advertised.
The remote PEs upon receiving this message, realize that this is a
special mass-withdraw message and they access the list of the vES's
for the specified color. Next, they initiate mass-withdraw procedure
for each of the vES's in the list.
5.4. Port Failure Handling for Single-Active vES's in PBB-EVPN
When a large number of 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 vES's. If the
number of EVCs corresponding to the Single-Active vES's for that
physical port is in 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 BMAC SA, then upon the port failure, the PE MUST use
the EVPN MAC route withdrawal message to signal the flush
2) If the PE shared MAC address is used for PBB encapsulation as BMAC
SA, then upon the port failure, the PE MUST re-advertise this MAC
route with the MAC Mobility Extended Community to signal the flush
The first method is recommended because it reduces the scope of
flushing the most.
5.5. Fast Convergence in PBB-EVPN
As described above, when a large number of EVCs are aggregated via a
physical port on a PE; where each EVC corresponds to a vES, then the
port failure impacts all the associated EVCs and their corresponding
vES's. Two actions must be taken as the result of such port failure:
- Flushing of all CMACs associated with the BMAC of the failed port
for the impacted I-SIDs
- DF election for all impacted vES's associated with the failed port
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Section 5.4 describes how to flush CMAC address in the most optimum
way - e.g., to flush least number of CMAC addresses for the impacted
I-SIDs. This section describes how to perform DF election in the most
optimum way - e.g., to trigger DF election for all impacted vES's
(which can be in thousands) among the participating PEs via a single
BGP message as opposed to sending thousands of BGP messages - one per
vES.
In order to devise such fast convergence mechanism that can be
triggered via a single BGP message, all vES's associated with a given
physical port (e.g., ENNI) are colored with the same color
representing that physical port. The MAC address of the physical port
is used for this coloring purposes and when the PE advertises an ES
route for a vES associated with that physical port, it advertises it
with an EVPN Router's MAC Extended Community indicating the color of
that port.
The receiving PEs take note of this color and for each such color,
they create a list of vES's associated with this color (with this MAC
address). Now, when a port failure occurs, the impacted PE needs to
notify the other PEs of this color so that these PEs can identify all
the impacted vES's associated with that color (from the above list)
and re-execute DF election procedures for all the impacted vES's.
In PBB-EVPN, there are two ways to convey this color to other PEs
upon a port failure - one corresponding to each method for signaling
flush message as described in section 5.4. If for PBB encapsulation,
the MAC address of the physical port is used as BMAC SA, then upon
the port failure, the PE sends MAC withdrawal message with the MAC
address of the failed port as the color. However, if for PBB
encapsulation, the shared MAC address of the PE (dedicated for all
Single-Active vES's) is used as BMAC SA, then upon the port failure,
the PE re-advertises the MAC route (that carries the shared BMAC)
along with this new EVPN Router's MAC Extended Community to indicate
the color along with MAC Mobility Extended Community.
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+-----+
+----+ | | +---+
| 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 5: Fast Convergence Upon ENNI Failure
The following describes the procedure for coloring vES's and fast
convergence using this color in more details:
1- When a vES is configured, the PE colors the vES with the MAC
address of the corresponding physical port and advertises the
Ethernet Segment route for this vES with this color.
2- All other PEs (in the redundancy group) take note of this color
and add the vES to the list for this color.
3- Upon the occurrence of a port failure (e.g., an ENNI failure), the
PE sends the flush message in one of the two ways described above
indicating this color. The PE should prioritize sending this flush
message over ES route withdrawal messages of impacted vES's.
4- On reception of the flush message, other PEs use this info to
flush their impacted CMACs and to initiate DF election procedures
across all their affected vES's.
5- The PE with the physical port failure (ENNI failure), also sends
ES route withdrawal for every impacted vES's. The other PEs upon
receiving these messages, clear up their BGP tables. It should be
noted the ES route withdrawal messages are not used for executing DF
election procedures by the receiving PEs.
6. BGP Encoding
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This document defines one new BGP Extended Community for EVPN.
6.1. I-SID Extended Community
A new EVPN BGP Extended Community called I-SID is introduced. This
new extended community is a transitive extended community with the
Type field of 0x06 (EVPN) and the Sub-Type of 0x07.
The I-SID Extended Community is encoded as an 8-octet value as
follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=0x06 | Sub-Type=0x07 | Base I-SID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cont. | Bit Map (24 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: I-SID Extended Community
This extended community is used to indicate the list of I-SIDs
associated with a given Ethernet Segment.
24-bit map represents the next 24 I-SID after the base I-SID. For
example based I-SID of 10025 with 24-bit map of zero means, only a
single I-SID of 10025. I-SID of 10025 with bit map of 0x000001 means
there are two I-SIDs, 10025 and 10026.
7. Acknowledgements
The authors would like to thanks Mei Zhang and Jose Liste for their
reviews and feedbacks of this document.
8. 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
processing of Ethernet Segment route for vES in this document follows
that of physical ES in those RFCs.
9. IANA Considerations
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IANA has allocated sub-type value 7 in the "EVPN Extended Community
Sub-Types" registry defined in "https://www.iana.org/assignments/bgp-
extended-communities/bgp-extended-communities.xhtml#evpn" as follows:
SUB-TYPE NAME Reference
---- -------------- -------------
0x07 I-SID Ext Comm [draft-sajassi-bess-evpn-virtual-eth-segment]
It is requested from IANA to update the reference to this document.
10. Intellectual Property Considerations
This document is being submitted for use in IETF standards
discussions.
11. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC2119
Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.
[RFC7432] Sajassi, et al., "BGP MPLS-Based Ethernet VPN", RFC 7432,
February 2015.
[RFC7623] Sajassi, et al., "Provider Backbone Bridging Combined with
Ethernet VPN (PBB-EVPN)", RFC 7623, September 2015.
[RFC8214] Boutrus, et al., "Virtual Private Wire Service Support in
Ethernet VPN", RFC 8214, August 2017.
[EVPN-IRB] Sajassi, et al., "Integrated Routing and Bridging in
EVPN", draft-ietf-bess-evpn-inter-subnet-forwarding-05, July 2018.
12. Informative References
[RFC7209] Sajassi, et al., "Requirements for Ethernet VPN (EVPN)",
RFC 7209, May 2014.
[RFC7080] Sajassi, A., Salam, S., Bitar, N., and F. Balus, "Virtual
Private LAN Service (VPLS) Interoperability with Provider
Backbone Bridges", RFC 7080, December 2013.
13. Authors' Addresses
Ali Sajassi
Cisco Systems
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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
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