Internet DRAFT - draft-ietf-bess-evpn-igmp-mld-proxy
draft-ietf-bess-evpn-igmp-mld-proxy
BESS WorkGroup A. Sajassi
Internet-Draft S. Thoria
Intended status: Standards Track M. Mishra
Expires: September 23, 2022 Cisco Systems
K. Patel
Arrcus
J. Drake
W. Lin
Juniper Networks
March 22, 2022
IGMP and MLD Proxy for EVPN
draft-ietf-bess-evpn-igmp-mld-proxy-21
Abstract
This document describes how to support efficiently endpoints running
IGMP(Internet Group Management Protocol) or MLD (Multicast Listener
Discovery) for the multicast services over an EVPN network by
incorporating IGMP/MLD proxy procedures on EVPN (Ethernet VPN) PEs.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on September 23, 2022.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Specification of Requirements . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. IGMP/MLD Proxy . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Proxy Reporting . . . . . . . . . . . . . . . . . . . . . 6
4.1.1. IGMP/MLD Membership Report Advertisement in BGP . . . 7
4.1.2. IGMP/MLD Leave Group Advertisement in BGP . . . . . . 9
4.2. Proxy Querier . . . . . . . . . . . . . . . . . . . . . . 9
5. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.1. PE with only attached hosts for a given subnet . . . . . 11
5.2. PE with a mix of attached hosts and multicast source . . 12
5.3. PE with a mix of attached hosts, a multicast source and a
router . . . . . . . . . . . . . . . . . . . . . . . . . 12
6. All-Active Multi-Homing . . . . . . . . . . . . . . . . . . . 12
6.1. Local IGMP/MLD Membership Report Synchronization . . . . 12
6.2. Local IGMP/MLD Leave Group Synchronization . . . . . . . 13
6.2.1. Remote Leave Group Synchronization . . . . . . . . . 14
6.2.2. Common Leave Group Synchronization . . . . . . . . . 14
6.3. Mass Withdraw of Multicast Membership Report Sync route
in case of failure . . . . . . . . . . . . . . . . . . . 15
7. Single-Active Multi-Homing . . . . . . . . . . . . . . . . . 15
8. Selective Multicast Procedures for IR tunnels . . . . . . . . 15
9. BGP Encoding . . . . . . . . . . . . . . . . . . . . . . . . 16
9.1. Selective Multicast Ethernet Tag Route . . . . . . . . . 16
9.1.1. Constructing the Selective Multicast Ethernet Tag
route . . . . . . . . . . . . . . . . . . . . . . . . 18
9.1.2. Reconstructing IGMP / MLD Membership Reports from
Selective Multicast Route . . . . . . . . . . . . . . 19
9.1.3. Default Selective Multicast Route . . . . . . . . . . 20
9.2. Multicast Membership Report Synch Route . . . . . . . . . 21
9.2.1. Constructing the Multicast Membership Report Synch
Route . . . . . . . . . . . . . . . . . . . . . . . . 22
9.2.2. Reconstructing IGMP / MLD Membership Reports from
Multicast Membership Report Sync Route . . . . . . . 23
9.3. Multicast Leave Synch Route . . . . . . . . . . . . . . . 24
9.3.1. Constructing the Multicast Leave Synch Route . . . . 26
9.3.2. Reconstructing IGMP / MLD Leave from Multicast Leave
Sync Route . . . . . . . . . . . . . . . . . . . . . 27
9.4. Multicast Flags Extended Community . . . . . . . . . . . 28
9.5. EVI-RT Extended Community . . . . . . . . . . . . . . . . 29
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9.6. Rewriting of RT ECs and EVI-RT ECs by ASBRs . . . . . . . 31
9.7. BGP Error Handling . . . . . . . . . . . . . . . . . . . 32
10. IGMP Version 1 Membership Report . . . . . . . . . . . . . . 32
11. Security Considerations . . . . . . . . . . . . . . . . . . . 32
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32
12.1. EVPN Extended Community Sub-Types Registrations . . . . 32
12.2. EVPN Route Type Registration . . . . . . . . . . . . . . 33
12.3. Multicast Flags Extended Community Registry . . . . . . 33
13. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 33
14. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 34
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 34
15.1. Normative References . . . . . . . . . . . . . . . . . . 34
15.2. Informative References . . . . . . . . . . . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35
1. Introduction
In DC applications, a point of delivery (POD) can consist of a
collection of servers supported by several top of rack (ToR) and
spine switches. This collection of servers and switches are self
contained and may have their own control protocol for intra-POD
communication and orchestration. However, EVPN is used as standard
way of inter-POD communication for both intra-DC and inter-DC. A
subnet can span across multiple PODs and DCs. EVPN provides a robust
multi-tenant solution with extensive multi-homing capabilities to
stretch a subnet (VLAN) across multiple PODs and DCs. There can be
many hosts (several hundreds) attached to a subnet that is stretched
across several PODs and DCs.
These hosts express their interests in multicast groups on a given
subnet/VLAN by sending IGMP/MLD Membership Reports for their
interested multicast group(s). Furthermore, an IGMP/MLD router
periodically sends membership queries to find out if there are hosts
on that subnet that are still interested in receiving multicast
traffic for that group. The IGMP/MLD Proxy solution described in
this document accomplishes three objectives:
1. Reduce flooding of IGMP/MLD messages: just like the ARP/ND
suppression mechanism in EVPN to reduce the flooding of ARP
messages over EVPN, it is also desired to have a mechanism to
reduce the flooding of IGMP/MLD messages (both Queries and
Membership Reports) in EVPN.
2. Distributed anycast multicast proxy: it is desirable for the EVPN
network to act as a distributed anycast multicast router with
respect to IGMP/MLD proxy function for all the hosts attached to
that subnet.
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3. Selective Multicast: to forward multicast traffic over EVPN
network such that it only gets forwarded to the PEs that have
interest in the multicast group(s). This document shows how this
objective may be achieved when Ingress Replication is used to
distribute the multicast traffic among the PEs. Procedures for
supporting selective multicast using P2MP tunnels can be found in
[I-D.ietf-bess-evpn-bum-procedure-updates]
The first two objectives are achieved by using IGMP/MLD proxy on the
PE. The third objective is achieved by setting up a multicast tunnel
only among the PEs that have interest in that multicast group(s)
based on the trigger from IGMP/MLD proxy processes. The proposed
solutions for each of these objectives are discussed in the following
sections.
2. Specification of Requirements
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.
3. Terminology
o AC: Attachment Circuit.
o All-Active Redundancy Mode: When all PEs attached to an Ethernet
segment are allowed to forward known unicast traffic to/from that
Ethernet segment for a given VLAN, then the Ethernet segment is
defined to be operating in All-Active redundancy mode.
o BD: Broadcast Domain. As per [RFC7432], an EVI consists of a
single or multiple BDs. In case of VLAN-bundle and VLAN-aware
bundle service model, an EVI contains multiple BDs. Also, in this
document, BD and subnet are equivalent terms.
o DC: Data Center
o Ethernet Segment (ES): When a customer site (device or network) is
connected to one or more PEs via a set of Ethernet links.
o Ethernet Segment Identifier (ESI): A unique non-zero identifier
that identifies an Ethernet Segment.
o Ethernet Tag: It identifies a particular broadcast domain, e.g., a
VLAN. An EVPN instance consists of one or more broadcast domains.
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o EVI: An EVPN instance spanning the Provider Edge (PE) devices
participating in that EVPN
o EVPN: Ethernet Virtual Private Network
o IGMP: Internet Group Management Protocol
o IR: Ingress Replication
o MLD: Multicast Listener Discovery
o OIF: Outgoing Interface for multicast. It can be physical
interface, virtual interface or tunnel.
o PE: Provider Edge.
o POD: Point of Delivery
o S-PMSI: Selective P-Multicast Service Interface - a conceptual
interface for a PE to send customer multicast traffic to some of
the PEs in the same VPN.
o Single-Active Redundancy Mode: When only a single PE, among all
the PEs attached to an Ethernet segment, is allowed to forward
traffic to/from that Ethernet segment for a given VLAN, then the
Ethernet segment is defined to be operating in Single-Active
redundancy mode.
o SMET: Selective Multicast Ethernet Tag
o ToR: Top of Rack
This document also assumes familiarity with the terminology of
[RFC7432], [RFC3376], [RFC2236] . Though most of the place this
document uses term IGMP Membership Report, the text applies equally
for MLD Membership Report too. Similarly, text for IGMPv2 applies to
MLDv1 and text for IGMPv3 applies to MLDv2. IGMP / MLD version
encoding in BGP update is stated in Section 9
It is important to note when there is text considering whether a PE
indicates support for IGMP proxying, the corresponding behavior has a
natural analogue for indication of support for MLD proxying, and the
analogous requirements apply as well.
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4. IGMP/MLD Proxy
The IGMP Proxy mechanism is used to reduce the flooding of IGMP
messages over an EVPN network similar to ARP proxy used in reducing
the flooding of ARP messages over EVPN. It also provides a
triggering mechanism for the PEs to setup their underlay multicast
tunnels. The IGMP Proxy mechanism consists of two components:
1. Proxy for IGMP Membership Reports.
2. Proxy for IGMP Membership Queries.
The goal of IGMP and MLD proxying is to make the EVPN behave
seamlessly for the tenant systems with respect to multicast
operations, while using a more efficient delivery system for
signaling and delivery across the VPN. Accordingly, group state must
be tracked synchronously among the PEs serving the VPN, with join and
leave events propagated to the peer PEs, and each PE tracking the
state of each of its peer PEs with respect whether there are locally
attached group members (and in some cases, senders), what version(s)
of IGMP/MLD are in use for those locally attached group members, etc.
In order to perform this translation, each PE acts as an IGMP router
for the locally attached domain, and maintains the requisite state on
locally attached nodes, sends periodic membership queries, etc. The
role of EVPN SMET route propagation is to ensure that each PE's local
state is propagated to the other PEs so that they share a consistent
view of the overall IGMP Membership Request and Leave Group state.
It is important to note that the need to keep such local state can be
triggered by either local IGMP traffic or BGP EVPN signaling. In
most cases a local IGMP event will need to be signaled over EVPN,
though state initiated by received EVPN traffic will not always need
to be relayed to the locally attached domain.
4.1. Proxy Reporting
When IGMP protocol is used between hosts and their first hop EVPN
router (EVPN PE), Proxy-reporting is used by the EVPN PE to summarize
(when possible) reports received from downstream hosts and propagate
them in BGP to other PEs that are interested in the information.
This is done by terminating the IGMP Reports in the first hop PE, and
translating and exchanging the relevant information among EVPN BGP
speakers. The information is again translated back to IGMP message
at the recipient EVPN speaker. Thus it helps create an IGMP overlay
subnet using BGP. In order to facilitate such an overlay, this
document also defines a new EVPN route type NLRI, the EVPN Selective
Multicast Ethernet Tag route, along with its procedures to help
exchange and register IGMP multicast groups Section 9.
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4.1.1. IGMP/MLD Membership Report Advertisement in BGP
When a PE wants to advertise an IGMP Membership Report using the BGP
EVPN route, it follows the following rules (BGP encoding stated in
Section 9). Where first four rules are applicable to originator PE
and last three rules are applicable to remote PE processing SMET
routes:
Processing at BGP route originator:
1. When the first hop PE receives IGMP Membership Reports ,
belonging to the same IGMP version, from different attached hosts
for the same (*,G) or (S,G), it SHOULD send a single BGP message
corresponding to the very first IGMP Membership Request (BGP
update as soon as possible) for that (*,G) or (S,G). This is
because BGP is a stateful protocol and no further transmission of
the same report is needed. If the IGMP Membership Request is for
(*,G), then multicast group address MUST be sent along with the
corresponding version flag (v2 or v3) set. In case of IGMPv3,
the exclude flag MUST also be set to indicate that no source IP
address must be excluded (include all sources "*"). If the IGMP
Membership Report is for (S,G), then besides setting multicast
group address along with the version flag v3, the source IP
address and the IE flag MUST be set. It should be noted that
when advertising the EVPN route for (S,G), the only valid version
flag is v3 (v2 flags MUST be set to zero).
2. When the first hop PE receives an IGMPv3 Membership Report for
(S,G) on a given BD, it MUST advertise the corresponding EVPN
Selective Multicast Ethernet Tag (SMET) route regardless of
whether the source (S) is attached to itself or not in order to
facilitate the source move in the future.
3. When the first hop PE receives an IGMP version-X Membership
Report first for (*,G) and then later it receives an IGMP
version-Y Membership Report for the same (*,G), then it MUST re-
advertise the same EVPN SMET route with flag for version-Y set in
addition to any previously-set version flag(s). In other words,
the first hop PE MUST NOT withdraw the EVPN route before sending
the new route because the flag field is not part of BGP route key
processing.
4. When the first hop PE receives an IGMP version-X Membership
Report first for (*,G) and then later it receives an IGMPv3
Membership Report for the same multicast group address but for a
specific source address S, then the PE MUST advertise a new EVPN
SMET route with v3 flag set (and v2 reset). The IE flag also
need to be set accordingly. Since source IP address is used as
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part of BGP route key processing it is considered as a new BGP
route advertisement. When different version of IGMP Membership
Report are received, final state MUST be as per section 5.1 of
[RFC3376]. At the end of route processing local and remote group
record state MUST be as per section 5.1 of [RFC3376].
Processing at BGP route receiver:
1. When a PE receives an EVPN SMET route with more than one version
flag set, it will generate the corresponding IGMP report for
(*,G) for each version specified in the flags field. With
multiple version flags set, there must not be source IP address
in the received EVPN route. If there is, then an error SHOULD be
logged. If the v3 flag is set (in addition to v2), then the IE
flag MUST indicate "exclude". If not, then an error SHOULD be
logged. The PE MUST generate an IGMP Membership Report for that
(*,G) and each IGMP version in the version flag.
2. When a PE receives a list of EVPN SMET NLRIs in its BGP update
message, each with a different source IP address and the same
multicast group address, and the version flag is set to v3, then
the PE generates an IGMPv3 Membership Report with a record
corresponding to the list of source IP addresses and the group
address along with the proper indication of inclusion/exclusion.
3. Upon receiving EVPN SMET route(s) and before generating the
corresponding IGMP Membership Request(s), the PE checks to see
whether it has any CE multicast router for that BD on any of its
ES's . The PE provides such a check by listening for PIM Hello
messages on that AC (i.e, ES,BD). If the PE does have the
router's ACs, then the generated IGMP Membership Request(s) are
sent to those ACs. If it doesn't have any of the router's AC,
then no IGMP Membership Request(s) needs to be generated. This
is because sending IGMP Membership Requests to other hosts can
result in unintentionally preventing a host from joining a
specific multicast group using IGMPv2 - i.e., if the PE does not
receive a Membership Report from the host it will not forward
multicast data to it. Per [RFC4541] , when an IGMPv2 host
receives a Membership Report for a group address that it intends
to join, the host will suppress its own membership report for the
same group, and if the PE does not receive an IGMP Membership
Report from the host it will not forward multicast data to it.
In other words, an IGMPv2 Membership Report MUST NOT be sent on
an AC that does not lead to a CE multicast router. This message
suppression is a requirement for IGMPv2 hosts. This is not a
problem for hosts running IGMPv3 because there is no suppression
of IGMP Membership Reports.
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4.1.2. IGMP/MLD Leave Group Advertisement in BGP
When a PE wants to withdraw an EVPN SMET route corresponding to an
IGMPv2 Leave Group or IGMPv3 "Leave" equivalent message, it follows
the following rules, where first rule defines the procedure at
originator PE and last two rules talk about procedures at remote PE:
Processing at BGP route originator:
1. When a PE receives an IGMPv2 Leave Group or its "Leave"
equivalent message for IGMPv3 from its attached host, it checks
to see if this host is the last host that is interested in this
multicast group by sending a query for the multicast group. If
the host was indeed the last one (i.e. no responses are received
for the query), then the PE MUST re-advertises EVPN SMET
Multicast route with the corresponding version flag reset. If
this is the last version flag to be reset, then instead of re-
advertising the EVPN route with all version flags reset, the PE
MUST withdraw the EVPN route for that (*,G).
Processing at BGP route receiver:
1. When a PE receives an EVPN SMET route for a given (*,G), it
compares the received version flags from the route with its per-
PE stored version flags. If the PE finds that a version flag
associated with the (*,G) for the remote PE is reset, then the PE
MUST generate IGMP Leave for that (*,G) toward its local
interface (if any) attached to the multicast router for that
multicast group. It should be noted that the received EVPN route
MUST at least have one version flag set. If all version flags
are reset, it is an error because the PE should have received an
EVPN route withdraw for the last version flag. Error MUST be
considered as a BGP error and the PE MUST apply the "treat-as-
withdraw" procedure of [RFC7606].
2. When a PE receives an EVPN SMET route withdraw, it removes the
remote PE from its OIF list for that multicast group and if there
are no more OIF entries for that multicast group (either locally
or remotely), then the PE MUST stop responding to Membership
Queries from the locally attached router (if any). If there is a
source for that multicast group, the PE stops sending multicast
traffic for that source.
4.2. Proxy Querier
As mentioned in the previous sections, each PE MUST have proxy
querier functionality for the following reasons:
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1. To enable the collection of EVPN PEs providing L2VPN service to
act as distributed multicast router with Anycast IP address for
all attached hosts in that subnet.
2. To enable suppression of IGMP Membership Reports and Membership
Queries over MPLS/IP core.
5. Operation
Consider the EVPN network of Figure-1, where there is an EVPN
instance configured across the PEs shown in this figure (namely PE1,
PE2, and PE3). Let's consider that this EVPN instance consists of a
single bridge domain (single subnet) with all the hosts, sources, and
the multicast router connected to this subnet. PE1 only has
hosts(host denoted by Hx) connected to it. PE2 has a mix of hosts
and a multicast source. PE3 has a mix of hosts, a multicast source
(source denoted by Sx), and a multicast router (router denoted by
Rx). Furthermore, let's consider that for (S1,G1), R1 is used as the
multicast router. The following subsections describe the IGMP proxy
operation in different PEs with regard to whether the locally
attached devices for that subnet are:
o only hosts
o mix of hosts and multicast source
o mix of hosts, multicast source, and multicast router
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+--------------+
| |
| |
+----+ | | +----+
H1:(*,G1)v2 ---| | | | | |---- H6(*,G1)v2
H2:(*,G1)v2 ---| PE1| | IP/MPLS | | PE2|---- H7(S2,G2)v3
H3:(*,G1)v3 ---| | | Network | | |---- S2
H4:(S2,G2)v3 --| | | | | |
+----+ | | +----+
| |
+----+ | |
H5:(S1,G1)v3 --| | | |
S1 ---| PE3| | |
R1 ---| | | |
+----+ | |
| |
+--------------+
Figure 1: EVPN network
5.1. PE with only attached hosts for a given subnet
When PE1 receives an IGMPv2 Membership Report from H1, it does not
forward this Membership Report to any of its other ports (for this
subnet) because all these local ports are associated with the hosts.
PE1 sends an EVPN Multicast Group route corresponding to this
Membership Report for (*,G1) and setting v2 flag. This EVPN route is
received by PE2 and PE3 that are the members of the same BD (i.e.,
same EVI in case of VLAN-based service or EVI,VLAN in case of VLAN-
aware bundle service). PE3 reconstructs the IGMPv2 Membership Report
from this EVPN BGP route and only sends it to the port(s) with
multicast routers attached to it (for that subnet). In this example,
PE3 sends the reconstructed IGMPv2 Membership Report for (*,G1) only
to R1. Furthermore, even though PE2 receives the EVPN BGP route, it
does not send it to any of its ports for that subnet; viz, ports
associated with H6 and H7.
When PE1 receives the second IGMPv2 Membership Report from H2 for the
same multicast group (*,G1), it only adds that port to its OIF list
but it doesn't send any EVPN BGP route because there is no change in
information. However, when it receives the IGMPv3 Membership Report
from H3 for the same (*,G1). Besides adding the corresponding port
to its OIF list, it re-advertises the previously sent EVPN SMET route
with the v3 and exclude flag set.
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Finally when PE1 receives the IGMPv3 Membership Report from H4 for
(S2,G2), it advertises a new EVPN SMET route corresponding to it.
5.2. PE with a mix of attached hosts and multicast source
The main difference in this case is that when PE2 receives the IGMPv3
Membership Report from H7 for (S2,G2), it does advertise it in BGP to
support source move even though PE2 knows that S2 is attached to its
local AC. PE2 adds the port associated with H7 to its OIF list for
(S2,G2). The processing for IGMPv2 received from H6 is the same as
the IGMPv2 Membership Report described in previous section.
5.3. PE with a mix of attached hosts, a multicast source and a router
The main difference in this case relative to the previous two
sections is that IGMP v2/v3 Membership Report messages received
locally need to be sent to the port associated with router R1.
Furthermore, the Membership Reports received via BGP (SMET) need to
be passed to the R1 port but filtered for all other ports.
6. All-Active Multi-Homing
Because the LAG flow hashing algorithm used by the CE is unknown at
the PE, in an All-Active redundancy mode it must be assumed that the
CE can send a given IGMP message to any one of the multi-homed PEs,
either DF or non-DF; i.e., different IGMP Membership Request messages
can arrive at different PEs in the redundancy group and furthermore
their corresponding Leave messages can arrive at PEs that are
different from the ones that received the Membership Report.
Therefore, all PEs attached to a given ES must coordinate IGMP
Membership Request and Leave Group (x,G) state, where x may be either
'*' or a particular source S, for each BD on that ES. Each PE has a
local copy of that state and the EVPN signaling serves to synchronize
state across PEs. This allows the DF for that (ES,BD) to correctly
advertise or withdraw a Selective Multicast Ethernet Tag (SMET) route
for that (x,G) group in that BD when needed. All-Active multihoming
PEs for a given ES MUST support IGMP synchronization procedures
described in this section if they need to perform IGMP proxy for
hosts connected to that ES.
6.1. Local IGMP/MLD Membership Report Synchronization
When a PE, either DF or non-DF, receives on a given multihomed ES
operating in All-Active redundancy mode, an IGMP Membership Report
for (x,G), it determines the BD to which the IGMP Membership Report
belongs. If the PE doesn't already have local IGMP Membership
Request (x,G) state for that BD on that ES, it MUST instantiate local
IGMP Membership Request (x,G) state and MUST advertise a BGP IGMP
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Membership Report Synch route for that (ES,BD). Local IGMP
Membership Request (x,G) state refers to IGMP Membership Request
(x,G) state that is created as a result of processing an IGMP
Membership Report for (x,G).
The IGMP Membership Report Synch route MUST carry the ES-Import RT
for the ES on which the IGMP Membership Report was received. Thus it
MUST only be imported by the PEs attached to that ES and not any
other PEs.
When a PE, either DF or non-DF, receives an IGMP Membership Report
Synch route it installs that route and if it doesn't already have
IGMP Membership Request (x,G) state for that (ES,BD), it MUST
instantiate that IGMP Membership Request (x,G) state - i.e., IGMP
Membership Request (x,G) state is the union of the local IGMP
Membership Report (x,G) state and the installed IGMP Membership
Report Synch route. If the DF did not already advertise (originate)
a SMET route for that (x,G) group in that BD, it MUST do so now.
When a PE, either DF or non-DF, deletes its local IGMP Membership
Request (x,G) state for that (ES,BD), it MUST withdraw its BGP IGMP
Membership Report Synch route for that (ES,BD).
When a PE, either DF or non-DF, receives the withdrawal of an IGMP
Membership Report Synch route from another PE it MUST remove that
route. When a PE has no local IGMP Membership Request (x,G) state
and it has no installed IGMP Membership Report Synch routes, it MUST
remove IGMP Membership Request (x,G) state for that (ES,BD). If the
DF no longer has IGMP Membership Request (x,G) state for that BD on
any ES for which it is DF, it MUST withdraw its SMET route for that
(x,G) group in that BD.
In other words, a PE advertises an SMET route for that (x,G) group in
that BD when it has IGMP Membership Request (x,G) state in that BD on
at least one ES for which it is DF and it withdraws that SMET route
when it does not have IGMP Membership Request (x,G) state in that BD
on any ES for which it is DF.
6.2. Local IGMP/MLD Leave Group Synchronization
When a PE, either DF or non-DF, receives, on a given multihomed ES
operating in All-Active redundancy mode, an IGMP Leave Group message
for (x,G) from the attached CE, it determines the BD to which the
IGMPv2 Leave Group belongs. Regardless of whether it has IGMP
Membership Request (x,G) state for that (ES,BD), it initiates the
(x,G) leave group synchronization procedure, which consists of the
following steps:
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1. It computes the Maximum Response Time, which is the duration of
(x,G) leave group synchronization procedure. This is the product
of two locally configured values, Last Member Query Count and
Last Member Query Interval (described in Section 3 of [RFC2236]),
plus a delta corresponding to the time it takes for a BGP
advertisement to propagate between the PEs attached to the
multihomed ES (delta is a consistently configured value on all
PEs attached to the multihomed ES).
2. It starts the Maximum Response Time timer. Note that the receipt
of subsequent IGMP Leave Group messages or BGP Leave Synch routes
for (x,G) do not change the value of a currently running Maximum
Response Time timer and are ignored by the PE.
3. It initiates the Last Member Query procedure described in
Section 3 of [RFC2236]; viz, it sends a number of Group-Specific
Query (x,G) messages (Last Member Query Count) at a fixed
interval (Last Member Query Interval) to the attached CE.
4. It advertises an IGMP Leave Synch route for that that (ES,BD).
This route notifies the other multihomed PEs attached to the
given multihomed ES that it has initiated an (x,G) leave group
synchronization procedure; i.e., it carries the ES-Import RT for
the ES on which the IGMP Leave Group was received. It also
contains the Maximum Response Time.
5. When the Maximum Response Timer expires, the PE that has
advertised the IGMP Leave Synch route withdraws it.
6.2.1. Remote Leave Group Synchronization
When a PE, either DF or non-DF, receives an IGMP Leave Synch route it
installs that route and it starts a timer for (x,G) on the specified
(ES,BD) whose value is set to the Maximum Response Time in the
received IGMP Leave Synch route. Note that the receipt of subsequent
IGMPv2 Leave Group messages or BGP Leave Synch routes for (x,G) do
not change the value of a currently running Maximum Response Time
timer and are ignored by the PE.
6.2.2. Common Leave Group Synchronization
If a PE attached to the multihomed ES receives an IGMP Membership
Report for (x,G) before the Maximum Response Time timer expires, it
advertises a BGP IGMP Membership Report Synch route for that (ES,BD).
If it doesn't already have local IGMP Membership Request (x,G) state
for that (ES,BD), it instantiates local IGMP Membership Request (x,G)
state. If the DF is not currently advertising (originating) a SMET
route for that (x,G) group in that BD, it does so now.
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If a PE attached to the multihomed ES receives an IGMP Membership
Report Synch route for (x,G) before the Maximum Response Time timer
expires, it installs that route and if it doesn't already have IGMP
Membership Request (x,G) state for that BD on that ES, it
instantiates that IGMP Membership Request (x,G) state. If the DF has
not already advertised (originated) a SMET route for that (x,G) group
in that BD, it does so now.
When the Maximum Response Timer expires a PE that has advertised an
IGMP Leave Synch route, withdraws it. Any PE attached to the
multihomed ES, that started the Maximum Response Time and has no
local IGMP Membership Request (x,G) state and no installed IGMP
Membership Report Synch routes, it removes IGMP Membership Request
(x,G) state for that (ES,BD). If the DF no longer has IGMP
Membership Request (x,G) state for that BD on any ES for which it is
DF, it withdraws its SMET route for that (x,G) group in that BD.
6.3. Mass Withdraw of Multicast Membership Report Sync route in case of
failure
A PE which has received an IGMP Membership Request would have synced
the IGMP Membership Report by the procedure defined in section 6.1.
If a PE with local Membership Report state goes down or the PE to CE
link goes down, it would lead to a mass withdraw of multicast routes.
Remote PEs (PEs where these routes were remote IGMP Membership
Reports) SHOULD NOT remove the state immediately; instead General
Query SHOULD be generated to refresh the states. There are several
ways to detect failure at a peer, e.g. using IGP next hop tracking or
ES route withdraw.
7. Single-Active Multi-Homing
Note that to facilitate state synchronization after failover, the PEs
attached to a multihomed ES operating in Single-Active redundancy
mode SHOULD also coordinate IGMP Membership Report (x,G) state. In
this case all IGMP Membership Report messages are received by the DF
and distributed to the non-DF PEs using the procedures described
above.
8. Selective Multicast Procedures for IR tunnels
If an ingress PE uses ingress replication, then for a given (x,G)
group in a given BD:
1. It sends (x,G) traffic to the set of PEs not supporting IGMP or
MLD Proxy. This set consists of any PE that has advertised an
IMET route for the BD without a Multicast Flags extended
community or with a Multicast Flags extended community in which
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neither the IGMP Proxy support nor the MLD Proxy support flags
are set.
2. It sends (x,G) traffic to the set of PEs supporting IGMP or MLD
Proxy and having listeners for that (x,G) group in that BD. This
set consists of any PE that has advertised an IMET route for the
BD with a Multicast Flags extended community in which the IGMP
Proxy support and/or the MLD Proxy support flags are set and that
has advertised a SMET route for that (x,G) group in that BD.
9. BGP Encoding
This document defines three new BGP EVPN routes to carry IGMP
Membership Reports. The route types are known as:
+ 6 - Selective Multicast Ethernet Tag Route
+ 7 - Multicast Membership Report Synch Route
+ 8 - Multicast Leave Synch Route
The detailed encoding and procedures for these route types are
described in subsequent sections.
9.1. Selective Multicast Ethernet Tag Route
A Selective Multicast Ethernet Tag route type specific EVPN NLRI
consists of the following:
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+---------------------------------------+
| RD (8 octets) |
+---------------------------------------+
| Ethernet Tag ID (4 octets) |
+---------------------------------------+
| Multicast Source Length (1 octet) |
+---------------------------------------+
| Multicast Source Address (variable) |
+---------------------------------------+
| Multicast Group Length (1 octet) |
+---------------------------------------+
| Multicast Group Address (Variable) |
+---------------------------------------+
| Originator Router Length (1 octet) |
+---------------------------------------+
| Originator Router Address (variable) |
+---------------------------------------+
| Flags (1 octet) |
+---------------------------------------+
For the purpose of BGP route key processing, all the fields are
considered to be part of the prefix in the NLRI except for the one-
octet flag field. The Flags fields are defined as follows:
0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+
| reserved |IE|v3|v2|v1|
+--+--+--+--+--+--+--+--+
o The least significant bit, bit 7 indicates support for IGMP
version 1. Since IGMP V1 is being deprecated sender MUST set it
as 0 for IGMP and receiver MUST ignore it.
o The second least significant bit, bit 6 indicates support for IGMP
version 2.
o The third least significant bit, bit 5 indicates support for IGMP
version 3.
o The fourth least significant bit, bit 4 indicates whether the
(S,G) information carried within the route-type is of an Include
Group type (bit value 0) or an Exclude Group type (bit value 1).
The Exclude Group type bit MUST be ignored if bit 5 is not set.
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o This EVPN route type is used to carry tenant IGMP multicast group
information. The flag field assists in distributing IGMP
Membership Report of a given host for a given multicast route.
The version bits help associate IGMP version of receivers
participating within the EVPN domain.
o The include/exclude (IE) bit helps in creating filters for a given
multicast route.
o If route is used for IPv6 (MLD) then bit 7 indicates support for
MLD version 1. The second least significant bit, bit 6 indicates
support for MLD version 2. Since there is no MLD version 3, in
case of IPv6 route third least significant bit MUST be 0. In case
of IPv6 routes, the fourth least significant bit MUST be ignored
if bit 6 is not set.
o Reserved bits MUST be set to 0 by sender. And receiver MUST
ignore the Reserved bits.
9.1.1. Constructing the Selective Multicast Ethernet Tag route
This section describes the procedures used to construct the Selective
Multicast Ethernet Tag (SMET) route.
The Route Distinguisher (RD) SHOULD be a Type 1 RD [RFC4364]. The
value field comprises an IP address of the PE (typically, the
loopback address) followed by a number unique to the PE.
The Ethernet Tag ID MUST be set as procedure defined in [RFC7432].
The Multicast Source Length MUST be set to length of the multicast
Source address in bits. If the Multicast Source Address field
contains an IPv4 address, then the value of the Multicast Source
Length field is 32. If the Multicast Source Address field contains
an IPv6 address, then the value of the Multicast Source Length field
is 128. In case of a (*,G) Membership Report, the Multicast Source
Length is set to 0.
The Multicast Source Address is the source IP address from the IGMP
Membership Report. In case of a (*,G), this field is not used.
The Multicast Group Length MUST be set to length of multicast group
address in bits. If the Multicast Group Address field contains an
IPv4 address, then the value of the Multicast Group Length field is
32. If the Multicast Group Address field contains an IPv6 address,
then the value of the Multicast Group Length field is 128.
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The Multicast Group Address is the Group address from the IGMP or MLD
Membership Report.
The Originator Router Length is the length of the Originator Router
Address in bits.
The Originator Router Address is the IP address of router originating
this route. The SMET Originator Router IP address MUST match that of
the IMET (or S-PMSI AD) route originated for the same EVI by the same
downstream PE.
The Flags field indicates the version of IGMP protocol from which the
Membership Report was received. It also indicates whether the
multicast group had the INCLUDE or EXCLUDE bit set.
Reserved bits MUST be set to 0. They can be defined in future by
other document.
IGMP is used to receive group membership information from hosts by
TORs. Upon receiving the hosts expression of interest of a
particular group membership, this information is then forwarded using
SMET route. The NLRI also keeps track of receiver's IGMP protocol
version and any source filtering for a given group membership. All
EVPN SMET routes are announced with per- EVI Route Target extended
communities.
9.1.2. Reconstructing IGMP / MLD Membership Reports from Selective
Multicast Route
This section describes the procedures used to reconstruct IGMP / MLD
Membership Reports from SMET route.
o If multicast group length is 32, route would be translated to IGMP
membership request. If multicast group length is 128, route would
be translated to MLD membership request.
o Multicast group address field would be translated to IGMP / MLD
group address.
o If Multicast source length is set to zero it would be translated
to any source (*). If multicast source length is non zero,
Multicast source address field would be translated to IGMP / MLD
source address.
o If flag bit 7 is set, it translates Membership report to be IGMP
V1 or MLD V1.
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o If flag bit 6 is set, it translates Membership report to be IGMP
V2 or MLD V2.
o Flag bit 5 is only valid for IGMP Membership report and if it is
set, it translates to IGMP V3 report.
o If IE flag is set, it translate to IGMP / MLD Exclude mode
membership report. If IE flag is not set (zero), it translates to
Include mode membership report.
9.1.3. Default Selective Multicast Route
If there is multicast router connected behind the EVPN domain, the PE
MAY originate a default SMET (*,*) to get all multicast traffic in
domain.
+--------------+
| |
| |
| | +----+
| | | |---- H1(*,G1)v2
| IP/MPLS | | PE1|---- H2(S2,G2)v3
| Network | | |---- S2
| | | |
| | +----+
| |
+----+ | |
+----+ | | | |
| | S1 ---| PE2| | |
|PIM |----R1 ---| | | |
|ASM | +----+ | |
| | | |
+----+ +--------------+
Figure 2: Multicast Router behind EVPN domain
Consider the EVPN network of Figure-2, where there is an EVPN
instance configured across the PEs. Let's consider that PE2 is
connected to multicast router R1 and there is a network running PIM
ASM behind R1. If there are receivers behind the PIM ASM network the
PIM Join would be forwarded to the PIM RP (Rendezvous Point). If
receivers behind PIM ASM network are interested in a multicast flow
originated by multicast source S2 (behind PE1), it is necessary for
PE2 to receive multicast traffic. In this case PE2 MUST originate a
(*,*) SMET route to receive all of the multicast traffic in the EVPN
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domain. To generate Wildcards (*,*) routes, the procedure from
[RFC6625] MUST be used.
9.2. Multicast Membership Report Synch Route
This EVPN route type is used to coordinate IGMP Membership Report
(x,G) state for a given BD between the PEs attached to a given ES
operating in All- Active (or Single-Active) redundancy mode and it
consists of following:
+--------------------------------------------------+
| RD (8 octets) |
+--------------------------------------------------+
| Ethernet Segment Identifier (10 octets) |
+--------------------------------------------------+
| Ethernet Tag ID (4 octets) |
+--------------------------------------------------+
| Multicast Source Length (1 octet) |
+--------------------------------------------------+
| Multicast Source Address (variable) |
+--------------------------------------------------+
| Multicast Group Length (1 octet) |
+--------------------------------------------------+
| Multicast Group Address (Variable) |
+--------------------------------------------------+
| Originator Router Length (1 octet) |
+--------------------------------------------------+
| Originator Router Address (variable) |
+--------------------------------------------------+
| Flags (1 octet) |
+--------------------------------------------------+
For the purpose of BGP route key processing, all the fields are
considered to be part of the prefix in the NLRI except for the one-
octet Flags field, whose fields are defined as follows:
0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+
| reserved |IE|v3|v2|v1|
+--+--+--+--+--+--+--+--+
o The least significant bit, bit 7 indicates support for IGMP
version 1.
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o The second least significant bit, bit 6 indicates support for IGMP
version 2.
o The third least significant bit, bit 5 indicates support for IGMP
version 3.
o The fourth least significant bit, bit 4 indicates whether the (S,
G) information carried within the route-type is of Include Group
type (bit value 0) or an Exclude Group type (bit value 1). The
Exclude Group type bit MUST be ignored if bit 5 is not set.
o Reserved bits MUST be set to 0.
The Flags field assists in distributing IGMP Membership Report of a
given host for a given multicast route. The version bits help
associate IGMP version of receivers participating within the EVPN
domain. The include/exclude bit helps in creating filters for a
given multicast route.
If route is being prepared for IPv6 (MLD) then bit 7 indicates
support for MLD version 1. The second least significant bit, bit 6
indicates support for MLD version 2. Since there is no MLD version
3, in case of IPv6 route third least significant bit MUST be 0. In
case of IPv6 route, the fourth least significant bit MUST be ignored
if bit 6 is not set.
9.2.1. Constructing the Multicast Membership Report Synch Route
This section describes the procedures used to construct the IGMP
Membership Report Synch route. Support for these route types is
optional. If a PE does not support this route, then it MUST NOT
indicate that it supports 'IGMP proxy' in the Multicast Flag extended
community for the EVIs corresponding to its multi-homed Ethernet
Segments (ESs).
An IGMP Membership Report Synch route MUST carry exactly one ES-
Import Route Target extended community, the one that corresponds to
the ES on which the IGMP Membership Report was received. It MUST
also carry exactly one EVI-RT EC, the one that corresponds to the EVI
on which the IGMP Membership Report was received. See Section 9.5
for details on how to encode and construct the EVI-RT EC.
The Route Distinguisher (RD) SHOULD be a Type 1 RD [RFC4364]. The
value field comprises an IP address of the PE (typically, the
loopback address) followed by a number unique to the PE.
The Ethernet Segment Identifier (ESI) MUST be set to the 10-octet
value defined for the ES.
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The Ethernet Tag ID MUST be set as per procedure defined in
[RFC7432].
The Multicast Source length MUST be set to length of Multicast Source
address in bits. If the Multicast Source field contains an IPv4
address, then the value of the Multicast Source Length field is 32.
If the Multicast Source field contains an IPv6 address, then the
value of the Multicast Source Length field is 128. In case of a
(*,G) Membership Report, the Multicast Source Length is set to 0.
The Multicast Source is the Source IP address of the IGMP Membership
Report. In case of a (*,G) Membership Report, this field does not
exist.
The Multicast Group length MUST be set to length of multicast group
address in bits. If the Multicast Group field contains an IPv4
address, then the value of the Multicast Group Length field is 32.
If the Multicast Group field contains an IPv6 address, then the value
of the Multicast Group Length field is 128.
The Multicast Group is the Group address of the IGMP Membership
Report.
The Originator Router Length is the length of the Originator Router
address in bits.
The Originator Router Address is the IP address of Router Originating
the prefix.
The Flags field indicates the version of IGMP protocol from which the
Membership Report was received. It also indicates whether the
multicast group had INCLUDE or EXCLUDE bit set.
Reserved bits MUST be set to 0.
9.2.2. Reconstructing IGMP / MLD Membership Reports from Multicast
Membership Report Sync Route
This section describes the procedures used to reconstruct IGMP / MLD
Membership Reports from Multicast Membership Report Sync route.
o If multicast group length is 32, route would be translated to IGMP
membership request. If multicast group length is 128, route would
be translated to MLD membership request.
o Multicast group address field would be translated to IGMP / MLD
group address.
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o If Multicast source length is set to zero it would be translated
to any source (*). If multicast source length is non zero,
Multicast source address field would be translated to IGMP / MLD
source address.
o If flag bit 7 is set, it translates Membership report to be IGMP
V1 or MLD V1.
o If flag bit 6 is set, it translates Membership report to be IGMP
V2 or MLD V2.
o Flag bit 5 is only valid for IGMP Membership report and if it is
set, it translates to IGMP V3 report.
o If IE flag is set, it translate to IGMP / MLD Exclude mode
membership report. If IE flag is not set (zero), it translates to
Include mode membership report.
9.3. Multicast Leave Synch Route
This EVPN route type is used to coordinate IGMP Leave Group (x,G)
state for a given BD between the PEs attached to a given ES operating
in All-Active (or Single-Active) redundancy mode and it consists of
following:
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+--------------------------------------------------+
| RD (8 octets) |
+--------------------------------------------------+
| Ethernet Segment Identifier (10 octets) |
+--------------------------------------------------+
| Ethernet Tag ID (4 octets) |
+--------------------------------------------------+
| Multicast Source Length (1 octet) |
+--------------------------------------------------+
| Multicast Source Address (variable) |
+--------------------------------------------------+
| Multicast Group Length (1 octet) |
+--------------------------------------------------+
| Multicast Group Address (Variable) |
+--------------------------------------------------+
| Originator Router Length (1 octet) |
+--------------------------------------------------+
| Originator Router Address (variable) |
+--------------------------------------------------+
| Reserved (4 octet) |
+--------------------------------------------------+
| Maximum Response Time (1 octet) |
+--------------------------------------------------+
| Flags (1 octet) |
+--------------------------------------------------+
For the purpose of BGP route key processing, all the fields are
considered to be part of the prefix in the NLRI except for the
Reserved, Maximum Response Time and the one-octet Flags field, whose
fields are defined as follows:
0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+
| reserved |IE|v3|v2|v1|
+--+--+--+--+--+--+--+--+
o The least significant bit, bit 7 indicates support for IGMP
version 1.
o The second least significant bit, bit 6 indicates support for IGMP
version 2.
o The third least significant bit, bit 5 indicates support for IGMP
version 3.
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o The fourth least significant bit, bit 4 indicates whether the (S,
G) information carried within the route-type is of Include Group
type (bit value 0) or an Exclude Group type (bit value 1). The
Exclude Group type bit MUST be ignored if bit 5 is not set.
o Reserved bits MUST be set to 0. They can be defined in future by
other document.
The Flags field assists in distributing IGMP Membership Report of a
given host for a given multicast route. The version bits help
associate IGMP version of receivers participating within the EVPN
domain. The include/exclude bit helps in creating filters for a
given multicast route.
If route is being prepared for IPv6 (MLD) then bit 7 indicates
support for MLD version 1. The second least significant bit, bit 6
indicates support for MLD version 2. Since there is no MLD version
3, in case of IPv6 route third least significant bit MUST be 0. In
case of IPv6 route, the fourth least significant bit MUST be ignored
if bit 6 is not set.
Reserved bits in flag MUST be set to 0. They can be defined in
future by other document.
9.3.1. Constructing the Multicast Leave Synch Route
This section describes the procedures used to construct the IGMP
Leave Synch route. Support for these route types is optional. If a
PE does not support this route, then it MUST NOT indicate that it
supports 'IGMP proxy' in Multicast Flag extended community for the
EVIs corresponding to its multi-homed Ethernet Segments.
An IGMP Leave Synch route MUST carry exactly one ES-Import Route
Target extended community, the one that corresponds to the ES on
which the IGMP Leave was received. It MUST also carry exactly one
EVI-RT EC, the one that corresponds to the EVI on which the IGMP
Leave was received. See Section 9.5 for details on how to form the
EVI-RT EC.
The Route Distinguisher (RD) SHOULD be a Type 1 RD [RFC4364]. The
value field comprises an IP address of the PE (typically, the
loopback address) followed by a number unique to the PE.
The Ethernet Segment Identifier (ESI) MUST be set to the 10-octet
value defined for the ES.
The Ethernet Tag ID MUST be set as per procedure defined in
[RFC7432].
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The Multicast Source length MUST be set to length of multicast source
address in bits. If the Multicast Source field contains an IPv4
address, then the value of the Multicast Source Length field is 32.
If the Multicast Source field contains an IPv6 address, then the
value of the Multicast Source Length field is 128. In case of a
(*,G) Membership Report, the Multicast Source Length is set to 0.
The Multicast Source is the Source IP address of the IGMP Membership
Report. In case of a (*,G) Membership Report, this field does not
exist.
The Multicast Group length MUST be set to length of multicast group
address in bits. If the Multicast Group field contains an IPv4
address, then the value of the Multicast Group Length field is 32.
If the Multicast Group field contains an IPv6 address, then the value
of the Multicast Group Length field is 128.
The Multicast Group is the Group address of the IGMP Membership
Report.
The Originator Router Length is the length of the Originator Router
address in bits.
The Originator Router Address is the IP address of Router Originating
the prefix.
Reserved field is not part of the route key. The originator MUST set
the reserved field to Zero , the receiver SHOULD ignore it and if it
needs to be propagated, it MUST propagate it unchanged
Maximum Response Time is value to be used while sending query as
defined in [RFC2236]
The Flags field indicates the version of IGMP protocol from which the
Membership Report was received. It also indicates whether the
multicast group had INCLUDE or EXCLUDE bit set.
9.3.2. Reconstructing IGMP / MLD Leave from Multicast Leave Sync Route
This section describes the procedures used to reconstruct IGMP / MLD
Leave from Multicast Leave Sync route.
o If multicast group length is 32, route would be translated to IGMP
Leave. If multicast group length is 128, route would be
translated to MLD Leave.
o Multicast group address field would be translated to IGMP / MLD
group address.
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o If Multicast source length is set to zero it would be translated
to any source (*). If multicast source length is non zero,
Multicast source address field would be translated to IGMP / MLD
source address.
o If flag bit 7 is set, it translates Membership report to be IGMP
V1 or MLD V1.
o If flag bit 6 is set, it translates Membership report to be IGMP
V2 or MLD V2.
o Flag bit 5 is only valid for IGMP Membership report and if it is
set, it translates to IGMP V3 report.
o If IE flag is set, it translate to IGMP / MLD Exclude mode Leave.
If IE flag is not set (zero), it translates to Include mode Leave.
o
9.4. Multicast Flags Extended Community
The 'Multicast Flags' extended community is a new EVPN extended
community. EVPN extended communities are transitive extended
communities with a Type field value of 6. IANA will assign a Sub-
Type from the 'EVPN Extended Community Sub-Types' registry.
A PE that supports IGMP and/or MLD Proxy on a given BD MUST attach
this extended community to the IMET route it advertises advertises
for that BD and it MUST set the IGMP and/or MLD Proxy Support flags
to 1. Note that an [RFC7432] compliant PE will not advertise this
extended community so its absence indicates that the advertising PE
does not support either IGMP or MLD Proxy.
The advertisement of this extended community enables more efficient
multicast tunnel setup from the source PE specially for ingress
replication - i.e., if an egress PE supports IGMP proxy but doesn't
have any interest in a given (x,G), it advertises its IGMP proxy
capability using this extended community but it does not advertise
any SMET route for that (x,G). When the source PE (ingress PE)
receives such advertisements from the egress PE, it does not
replicate the multicast traffic to that egress PE; however, it does
replicate the multicast traffic to the egress PEs that don't
advertise such capability even if they don't have any interests in
that (x,G).
A Multicast Flags extended community is encoded as an 8-octet value,
as follows:
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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=0x09 | Flags (2 Octets) |M|I|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The low-order (lease significant) two bits are defined as the "IGMP
Proxy Support and MLD Proxy Support" bit. The absence of this
extended community also means that the PE does not support IGMP
proxy. where:
o Type is 0x06 as registered with IANA for EVPN Extended
Communities.
o Sub-Type : 0x09
o Flags are two Octets value.
* Bit 15 (shown as I) defines IGMP Proxy Support. Value of 1 for
bit 15 means that PE supports IGMP Proxy. Value of 0 for bit
15 means that PE does not supports IGMP Proxy.
* Bit 14 (shown as M) defines MLD Proxy Support. Value of 1 for
bit 14 means that PE supports MLD Proxy. Value of 0 for bit 14
means that PE does not support MLD proxy.
* Bit 0 to 13 are reserved for future. Sender MUST set it 0 and
receiver MUST ignore it.
o Reserved bits are set to 0. Sender MUST set it to 0 and receiver
MUST ignore it.
If a router does not support this specification, it MUST NOT add
Multicast Flags Extended Community in BGP route. A router receiving
BGP update, if M and I both flag are zero (0), the router MUST treat
this Update as malformed. Receiver of such update MUST ignore the
extended community.
9.5. EVI-RT Extended Community
In EVPN, every EVI is associated with one or more Route Targets
(RTs). These Route Targets serve two functions:
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1. Distribution control: RTs control the distribution of the routes.
If a route carries the RT associated with a particular EVI, it
will be distributed to all the PEs on which that EVI exists.
2. EVI identification: Once a route has been received by a
particular PE, the RT is used to identify the EVI to which it
applies.
An IGMP Membership Report Synch or IGMP Leave Synch route is
associated with a particular combination of ES and EVI. These routes
need to be distributed only to PEs that are attached to the
associated ES. Therefore these routes carry the ES-Import RT for
that ES.
Since an IGMP Membership Report Synch or IGMP Leave Synch route does
not need to be distributed to all the PEs on which the associated EVI
exists, these routes cannot carry the RT associated with that EVI.
Therefore, when such a route arrives at a particular PE, the route's
RTs cannot be used to identify the EVI to which the route applies.
Some other means of associating the route with an EVI must be used.
This document specifies four new Extended Communities (EC) that can
be used to identify the EVI with which a route is associated, but
which do not have any effect on the distribution of the route. These
new ECs are known as the "Type 0 EVI-RT EC", the "Type 1 EVI-RT EC",
the "Type 2 EVI-RT EC", and the "Type 3 EVI-RT EC".
1. A Type 0 EVI-RT EC is an EVPN EC (type 6) of sub-type 0xA.
2. A Type 1 EVI-RT EC is an EVPN EC (type 6) of sub-type 0xB.
3. A Type 2 EVI-RT EC is an EVPN EC (type 6) of sub-type 0xC.
4. A Type 3 EVI-RT EC is an EVPN EC (type 6) of sub-type 0xD
Each IGMP Membership Report Synch or IGMP Leave Synch route MUST
carry exactly one EVI-RT EC. The EVI-RT EC carried by a particular
route is constructed as follows. Each such route is the result of
having received an IGMP Membership Report or an IGMP Leave message
from a particular BD. The route is said to be associated with that
BD. For each BD, there is a corresponding RT that is used to ensure
that routes "about" that BD are distributed to all PEs attached to
that BD. So suppose a given IGMP Membership Report Synch or Leave
Synch route is associated with a given BD, say BD1, and suppose that
the corresponding RT for BD1 is RT1. Then:
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o 0. If RT1 is a Transitive Two-Octet AS-specific EC, then the EVI-
RT EC carried by the route is a Type 0 EVI-RT EC. The value field
of the Type 0 EVI-RT EC is identical to the value field of RT1.
o 1. If RT1 is a Transitive IPv4-Address-specific EC, then the EVI-
RT EC carried by the route is a Type 1 EVI-RT EC. The value field
of the Type 1 EVI-RT EC is identical to the value field of RT1.
o 2. If RT1 is a Transitive Four-Octet-specific EC, then the EVI-RT
EC carried by the route is a Type 2 EVI-RT EC. The value field of
the Type 2 EVI-RT EC is identical to the value field of RT1.
o 3. If RT1 is a Transitive IPv6-Address-specific EC, then the EVI-
RT EC carried by the route is a Type 3 EVI-RT EC. The value field
of the Type 3 EVI-RT EC is identical to the value field of RT1.
An IGMP Membership Report Synch or Leave Synch route MUST carry
exactly one EVI-RT EC.
Suppose a PE receives a particular IGMP Membership Report Synch or
IGMP Leave Synch route, say R1, and suppose that R1 carries an ES-
Import RT that is one of the PE's Import RTs. If R1 has no EVI-RT
EC, or has more than one EVI-RT EC, the PE MUST apply the "treat-as-
withdraw" procedure of [RFC7606].
Note that an EVI-RT EC is not a Route Target Extended Community, is
not visible to the RT Constrain mechanism [RFC4684], and is not
intended to influence the propagation of routes by BGP.
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=n | RT associated with EVI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RT associated with the EVI (cont.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where the value of 'n' is 0x0A, 0x0B, 0x0C, or 0x0D corresponding to
EVI-RT type 0, 1, 2, or 3 respectively.
9.6. Rewriting of RT ECs and EVI-RT ECs by ASBRs
There are certain situations in which an ES is attached to a set of
PEs that are not all in the same AS, or not all operated by the same
provider. In some such situations, the RT that corresponds to a
particular EVI may be different in each AS. If a route is propagated
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from AS1 to AS2, an ASBR at the AS1/AS2 border may be provisioned
with a policy that removes the RTs that are meaningful in AS1 and
replaces them with the corresponding (i.e., RTs corresponding to the
same EVIs) RTs that are meaningful in AS2. This is known as RT-
rewriting.
Note that if a given route's RTs are rewritten, and the route carries
an EVI-RT EC, the EVI-RT EC needs to be rewritten as well.
9.7. BGP Error Handling
If a received BGP update contains Flags not in accordance with IGMP/
MLD version-X expectation, the PE MUST apply the "treat-as-withdraw"
procedure as per [RFC7606]
If a received BGP update is malformed such that BGP route keys cannot
be extracted, then BGP update MUST be considered as invalid.
Receiving PE MUST apply the "Session reset" procedure of [RFC7606].
10. IGMP Version 1 Membership Report
This document does not provide any detail about IGMPv1 processing.
Implementations are expected to only use IGMPv2 and above for IPv4
and MLDv1 and above for IPv6. IGMPv1 routes are considered invalid
and the PE MUST apply the "treat-as-withdraw" procedure as per
[RFC7606].
11. Security Considerations
This document describes a means to efficiently operate IGMP and MLD
on a subnet constructed across multiple PODs or DCs via an EVPN
solution. The security considerations for the operation of the
underlying EVPN and BGP substrate are described in [RFC7432], and
specific multicast considerations are outlined in [RFC6513] and
[RFC6514]. The EVPN and associated IGMP proxy provides a single
broadcast domain so the same security considerations of IGMPv2
[RFC2236], [RFC3376], MLD [RFC2710], or MLDv2 [RFC3810] apply.
12. IANA Considerations
12.1. EVPN Extended Community Sub-Types Registrations
IANA has allocated the following codepoints from the EVPN Extended
Community Sub-Types sub-registry of the BGP Extended Communities
registry.
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0x09 Multicast Flags Extended Community [this document]
0x0A EVI-RT Type 0 [this document]
0x0B EVI-RT Type 1 [this document]
0x0C EVI-RT Type 2 [this document]
IANA is requested to allocate a new codepoint from the EVPN Extended
Community sub-types registry for the following.
0x0D EVI-RT Type 3 [this document]
12.2. EVPN Route Type Registration
IANA has allocated the following EVPN route types from the EVPN Route
Type registry.
6 - Selective Multicast Ethernet Tag Route
7 - Multicast Membership Report Synch Route
8 - Multicast Leave Synch Route
12.3. Multicast Flags Extended Community Registry
The Multicast Flags Extended Community contains a 16-bit Flags field.
The bits are numbered 0-15, from high-order to low-order.
The registry should be initialized as follows:
Bit Name Reference Change Controller
---- -------------- ------------- ------------------
0 - 13 Unassigned
14 MLD Proxy Support This document. IETF
15 IGMP Proxy Support This document IETF
The registration policy should be "First Come First Served".
13. Acknowledgement
The authors would like to thank Stephane Litkowski, Jorge Rabadan,
Anoop Ghanwani, Jeffrey Haas, Krishna Muddenahally Ananthamurthy,
Swadesh Agrawal for reviewing and providing valuable comment.
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14. Contributors
Derek Yeung
Arrcus
Email: derek@arrcus.com
15. References
15.1. 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>.
[RFC2236] Fenner, W., "Internet Group Management Protocol, Version
2", RFC 2236, DOI 10.17487/RFC2236, November 1997,
<https://www.rfc-editor.org/info/rfc2236>.
[RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast
Listener Discovery (MLD) for IPv6", RFC 2710,
DOI 10.17487/RFC2710, October 1999,
<https://www.rfc-editor.org/info/rfc2710>.
[RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version
3", RFC 3376, DOI 10.17487/RFC3376, October 2002,
<https://www.rfc-editor.org/info/rfc3376>.
[RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
DOI 10.17487/RFC3810, June 2004,
<https://www.rfc-editor.org/info/rfc3810>.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <https://www.rfc-editor.org/info/rfc4364>.
[RFC4684] Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk,
R., Patel, K., and J. Guichard, "Constrained Route
Distribution for Border Gateway Protocol/MultiProtocol
Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual
Private Networks (VPNs)", RFC 4684, DOI 10.17487/RFC4684,
November 2006, <https://www.rfc-editor.org/info/rfc4684>.
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[RFC6513] Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February
2012, <https://www.rfc-editor.org/info/rfc6513>.
[RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", RFC 6514, DOI 10.17487/RFC6514, February 2012,
<https://www.rfc-editor.org/info/rfc6514>.
[RFC6625] Rosen, E., Ed., Rekhter, Y., Ed., Hendrickx, W., and R.
Qiu, "Wildcards in Multicast VPN Auto-Discovery Routes",
RFC 6625, DOI 10.17487/RFC6625, May 2012,
<https://www.rfc-editor.org/info/rfc6625>.
[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>.
[RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
Patel, "Revised Error Handling for BGP UPDATE Messages",
RFC 7606, DOI 10.17487/RFC7606, August 2015,
<https://www.rfc-editor.org/info/rfc7606>.
[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>.
15.2. Informative References
[I-D.ietf-bess-evpn-bum-procedure-updates]
Zhang, Z., Lin, W., Rabadan, J., Patel, K., and A.
Sajassi, "Updates on EVPN BUM Procedures", draft-ietf-
bess-evpn-bum-procedure-updates-14 (work in progress),
November 2021.
[RFC4541] Christensen, M., Kimball, K., and F. Solensky,
"Considerations for Internet Group Management Protocol
(IGMP) and Multicast Listener Discovery (MLD) Snooping
Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006,
<https://www.rfc-editor.org/info/rfc4541>.
Authors' Addresses
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Ali Sajassi
Cisco Systems
821 Alder Drive,
MILPITAS, CALIFORNIA 95035
UNITED STATES
Email: sajassi@cisco.com
Samir Thoria
Cisco Systems
821 Alder Drive,
MILPITAS, CALIFORNIA 95035
UNITED STATES
Email: sthoria@cisco.com
Mankamana Mishra
Cisco Systems
821 Alder Drive,
MILPITAS, CALIFORNIA 95035
UNITED STATES
Email: mankamis@cisco.com
Keyur PAtel
Arrcus
UNITED STATES
Email: keyur@arrcus.com
John Drake
Juniper Networks
Email: jdrake@juniper.net
Wen Lin
Juniper Networks
Email: wlin@juniper.net
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