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| author | Thomas Voss <mail@thomasvoss.com> | 2024-11-27 20:54:24 +0100 |
|---|---|---|
| committer | Thomas Voss <mail@thomasvoss.com> | 2024-11-27 20:54:24 +0100 |
| commit | 4bfd864f10b68b71482b35c818559068ef8d5797 (patch) | |
| tree | e3989f47a7994642eb325063d46e8f08ffa681dc /doc/rfc/rfc9251.txt | |
| parent | ea76e11061bda059ae9f9ad130a9895cc85607db (diff) | |
doc: Add RFC documents
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diff --git a/doc/rfc/rfc9251.txt b/doc/rfc/rfc9251.txt new file mode 100644 index 0000000..8a4adc4 --- /dev/null +++ b/doc/rfc/rfc9251.txt @@ -0,0 +1,1648 @@ + + + + +Internet Engineering Task Force (IETF) A. Sajassi +Request for Comments: 9251 S. Thoria +Category: Standards Track M. Mishra +ISSN: 2070-1721 Cisco Systems + K. Patel + Arrcus + J. Drake + W. Lin + Juniper Networks + June 2022 + + + Internet Group Management Protocol (IGMP) and Multicast Listener + Discovery (MLD) Proxies for Ethernet VPN (EVPN) + +Abstract + + This document describes how to support endpoints running the Internet + Group Management Protocol (IGMP) or Multicast Listener Discovery + (MLD) efficiently for the multicast services over an Ethernet VPN + (EVPN) network by incorporating IGMP/MLD Proxy procedures on EVPN + Provider Edges (PEs). + +Status of This Memo + + This is an Internet Standards Track document. + + This document is a product of the Internet Engineering Task Force + (IETF). It represents the consensus of the IETF community. It has + received public review and has been approved for publication by the + Internet Engineering Steering Group (IESG). Further information on + Internet Standards is available in Section 2 of RFC 7841. + + Information about the current status of this document, any errata, + and how to provide feedback on it may be obtained at + https://www.rfc-editor.org/info/rfc9251. + +Copyright Notice + + Copyright (c) 2022 IETF Trust and the persons identified as the + document authors. All rights reserved. + + This document is subject to BCP 78 and the IETF Trust's Legal + Provisions Relating to IETF Documents + (https://trustee.ietf.org/license-info) in effect on the date of + publication of this document. Please review these documents + carefully, as they describe your rights and restrictions with respect + to this document. Code Components extracted from this document must + include Revised BSD License text as described in Section 4.e of the + Trust Legal Provisions and are provided without warranty as described + in the Revised BSD License. + +Table of Contents + + 1. Introduction + 2. Specification of Requirements + 3. Terminology + 4. IGMP/MLD Proxy + 4.1. Proxy Reporting + 4.1.1. IGMP/MLD Membership Report Advertisement in BGP + 4.1.2. IGMP/MLD Leave Group Advertisement in BGP + 4.2. Proxy Querier + 5. Operation + 5.1. PE with Only Attached Hosts for a Given Subnet + 5.2. PE with a Mix of Attached Hosts and a Multicast Source + 5.3. PE with a Mix of Attached Hosts, a Multicast Source, and a + Router + 6. All-Active Multihoming + 6.1. Local IGMP/MLD Membership Report Synchronization + 6.2. Local IGMP/MLD Leave Group Synchronization + 6.2.1. Remote Leave Group Synchronization + 6.2.2. Common Leave Group Synchronization + 6.3. Mass Withdraw of the Multicast Membership Report Synch + Route in Case of Failure + 7. Single-Active Multihoming + 8. Selective Multicast Procedures for IR Tunnels + 9. BGP Encoding + 9.1. Selective Multicast Ethernet Tag Route + 9.1.1. Constructing the Selective Multicast Ethernet Tag Route + 9.1.2. Reconstructing IGMP/MLD Membership Reports from the + Selective Multicast Route + 9.1.3. Default Selective Multicast Route + 9.2. Multicast Membership Report Synch Route + 9.2.1. Constructing the Multicast Membership Report Synch + Route + 9.2.2. Reconstructing IGMP/MLD Membership Reports from a + Multicast Membership Report Synch Route + 9.3. Multicast Leave Synch Route + 9.3.1. Constructing the Multicast Leave Synch Route + 9.3.2. Reconstructing IGMP/MLD Leave from a Multicast Leave + Synch Route + 9.4. Multicast Flags Extended Community + 9.5. EVI-RT Extended Community + 9.6. Rewriting of RT ECs and EVI-RT ECs by ASBRs + 9.7. BGP Error Handling + 10. IGMP Version 1 Membership Report + 11. Security Considerations + 12. IANA Considerations + 12.1. EVPN Extended Community Sub-Types Registration + 12.2. EVPN Route Types Registration + 12.3. Multicast Flags Extended Community Registry + 13. References + 13.1. Normative References + 13.2. Informative References + Acknowledgements + Contributors + Authors' Addresses + +1. Introduction + + In data center (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 a + 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 multihoming 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/Neighbor + Discovery (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. + + 3. Selective multicast: This describes forwarding multicast traffic + over the EVPN network such that it only gets forwarded to the PEs + that have interests 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 Point-to- + Multipoint (P2MP) tunnels can be found in [EVPN-BUM]. + + The first two objectives are achieved by using the IGMP/MLD Proxy on + the PE. The third objective is achieved by setting up a multicast + tunnel among only the PEs that have interest in the 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 + + AC: Attachment Circuit + + 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. + + BD: Broadcast Domain. As per [RFC7432], an EVPN instance (EVI) + consists of a single BD or multiple BDs. In case of a VLAN bundle + and a VLAN-aware bundle service model, an EVI contains multiple + BDs. Also, in this document, BD and subnet are equivalent terms. + + DC: Data Center + + ES: Ethernet segment. This is when a customer site (device or + network) is connected to one or more PEs via a set of Ethernet + links. + + ESI: Ethernet Segment Identifier. This is a unique non-zero + identifier that identifies an Ethernet segment. + + Ethernet Tag: It identifies a particular broadcast domain, e.g., a + VLAN. An EVPN instance consists of one or more broadcast domains. + + EVI: EVPN Instance. This spans the Provider Edge (PE) devices + participating in that EVPN. + + EVPN: Ethernet Virtual Private Network + + IGMP: Internet Group Management Protocol + + IR: Ingress Replication + + MLD: Multicast Listener Discovery + + OIF: Outgoing Interface for multicast. It can be a physical + interface, virtual interface, or tunnel. + + PE: Provider Edge + + POD: Point of Delivery + + S-PMSI: Selective P-Multicast Service Interface. This is a + conceptual interface for a PE to send customer multicast traffic + to some of the PEs in the same VPN. + + 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. + + SMET: Selective Multicast Ethernet Tag + + ToR: Top of Rack + + This document also assumes familiarity with the terminology of + [RFC7432], [RFC3376], and [RFC2236]. When this document uses the + term "IGMP Membership Report", the text equally applies to the MLD + Membership Report. Similarly, text for IGMPv2 applies to MLDv1, and + text for IGMPv3 applies to MLDv2. IGMP/MLD version encoding in the + BGP update is stated in Section 9. + + It is important to note that when there is text considering whether a + PE indicates support for IGMP proxying, the corresponding behavior + has a natural analog for indicating support for MLD proxying, and the + analogous requirements apply as well. + +4. IGMP/MLD Proxy + + The IGMP Proxy mechanism is used to reduce the flooding of IGMP + messages over an EVPN network, similar to the ARP proxy used in + reducing the flooding of ARP messages over EVPN. It also provides a + triggering mechanism for the PEs to set up 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 to 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, maintains the + requisite state on locally attached nodes, sends periodic Membership + Queries, etc. The role of EVPN Selective Multicast Ethernet Tag + (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 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 Membership Reports in the first hop PE + and translating and exchanging the relevant information among EVPN + BGP speakers. The information is again translated back to an 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 Network Layer + Reachability Information (NLRI) and the EVPN SMET route, along with + its procedures to help exchange and register IGMP multicast groups; + see Section 9. + +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 proceeding rules (BGP encoding is stated + in Section 9). The first four rules are applicable to the originator + PE, and the last three rules are applicable to remote PE processing + SMET routes: + + Processing at the 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 the 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 the + Multicast Group Address along with the v3 flag, the source IP + address and the Include/Exclude (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 0). + + 2. When the first hop PE receives an IGMPv3 Membership Report for + (S,G) on a given BD, it MUST advertise the corresponding EVPN + 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 receives an IGMP version-Y + Membership Report for the same (*,G), then it MUST re-advertise + the same EVPN SMET route with the 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 Flags 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 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 the v3 flag set (and v2 reset). The IE flag also + needs to be set accordingly. Since the source IP address is used + as part of BGP route key processing, it is considered to be a new + BGP route advertisement. When different versions of IGMP + Membership Report are received, the final state MUST be as per + Section 5.1 of [RFC3376]. At the end of the route processing, + local and remote group record state MUST be as per Section 5.1 of + [RFC3376]. + + Processing at the 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 a 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 an EVPN SMET route(s) and before generating the + corresponding IGMP Membership Request(s), the PE checks to see + whether it has a Customer Edge (CE) multicast router for that BD + on any of its ESs . 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) is sent to those ACs. If it doesn't have any of the + router's ACs, 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. + +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 rules below. The first rule defines the procedure at the + originator PE, and the last two rules talk about procedures at the + remote PE: + + Processing at the 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-advertise the EVPN SMET 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 the 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), which is attached to the multicast router for + that multicast group. It should be noted that the received EVPN + route MUST have at least 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. An + error MUST be considered as a BGP error, and the PE MUST apply + the "treat-as-withdraw" procedure per [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: + + 1. to enable the collection of EVPN PEs providing Layer 2 Virtual + Private Network (L2VPN) service to act as a distributed multicast + router with an 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 in Figure 1, where there is an EVPN + instance configured across the PEs (namely PE1, PE2, and PE3). Let's + consider that this EVPN instance consists of a single bridge domain + (single subnet) with all the hosts and 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: + + * only hosts, + + * a mix of hosts and a multicast source, or + + * a mix of hosts, a multicast source, and a multicast router. + + +--------------+ + | | + | | + +----+ | | +----+ + 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 SMET route corresponding to this Membership Report + for (*,G1) and sets the v2 flag. This EVPN route is received by PE2 + and PE3, which are the members of the same BD (i.e., same EVI in case + of a VLAN-based service or EVI and VLAN in case of a 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 routes 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. + + 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 a Multicast Source + + The main difference in this case is that when PE2 receives the IGMPv3 + Membership Report from H7 for (S2,G2), it advertises it in BGP to + support the source moving, 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 the 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 IGMPv2/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 Multihoming + + Because the Link Aggregation Group (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 multihomed PEs, either Designated Forwarder (DF) or non-DF, + i.e., different IGMP Membership Request messages can arrive at + different PEs in the redundancy group. 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 Ethernet segment (ES) must coordinate the + 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 that state across PEs. This allows the DF for that + (ES,BD) to correctly advertise or withdraw a 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 an IGMP Membership Report + for (x,G) on a given multihomed ES operating in All-Active redundancy + mode, it determines the BD to which the IGMP Membership Report + belongs. If the PE doesn't already have the local IGMP Membership + Request (x,G) state for that BD on that ES, it MUST instantiate that + local IGMP Membership Request (x,G) state and MUST advertise a BGP + IGMP Membership Report Synch route for that (ES,BD). The local IGMP + Membership Request (x,G) state refers to the 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 Route + Target (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 + the IGMP Membership Request (x,G) state for that (ES,BD), it MUST + instantiate that IGMP Membership Request (x,G) state, i.e., the 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 that IGMP Membership Request (x,G) state for that (ES,BD). If + the DF no longer has the IGMP Membership Request (x,G) state for that + BD on any ES for which it is the DF, it MUST withdraw its SMET route + for that (x,G) group in that BD. + + In other words, a PE advertises a SMET route for that (x,G) group in + that BD when it has the IGMP Membership Request (x,G) state on at + least one ES for which it is the DF, and it withdraws that SMET route + when it does not have an IGMP Membership Request (x,G) state in that + BD on any ES for which it is the DF. + +6.2. Local IGMP/MLD Leave Group Synchronization + + When a PE, either DF or non-DF, receives an IGMP Leave Group message + for (x,G) from the attached CE on a given multihomed ES operating in + All-Active redundancy mode, it determines the BD to which the IGMPv2 + Leave Group belongs. Regardless of whether it has the 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: + + 1. It computes the Maximum Response Time, which is the duration of + the (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 (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 Time 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 the local IGMP Membership Request (x,G) + state for that (ES,BD), it instantiates that 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. + + 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 the + 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 Time timer expires, a PE that has + advertised an IGMP Leave Synch route withdraws it. Any PE attached + to the multihomed ES, which started the Maximum Response Time and has + no local IGMP Membership Request (x,G) state and no installed IGMP + Membership Report Synch routes, removes the IGMP Membership Request + (x,G) state for that (ES,BD). If the DF no longer has the IGMP + Membership Request (x,G) state for that BD on any ES for which it is + the DF, it withdraws its SMET route for that (x,G) group in that BD. + +6.3. Mass Withdraw of the Multicast Membership Report Synch Route in + Case of Failure + + A PE that 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 the 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 Multihoming + + Note that to facilitate state synchronization after failover, the PEs + attached to a multihomed ES operating in Single-Active redundancy + mode SHOULD also coordinate the 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 Proxies. This set consists of any PE that has advertised an + Inclusive Multicast Ethernet Tag (IMET) route for the BD without + a Multicast Flags Extended Community or with a Multicast Flags + Extended Community in which 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 + Proxies and has 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 SMET route-type-specific EVPN NLRI consists of the following: + + +---------------------------------------+ + | 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 + 1-octet Flags field. The Flags fields are defined as follows: + + 0 1 2 3 4 5 6 7 + +--+--+--+--+--+--+--+--+ + | reserved |IE|v3|v2|v1| + +--+--+--+--+--+--+--+--+ + + * The least significant bit (bit 7) indicates support for IGMP + version 1. Since IGMPv1 is being deprecated, the sender MUST set + it to 0 for IGMP and the receiver MUST ignore it. + + * The second least significant bit (bit 6) indicates support for + IGMP version 2. + + * The third least significant bit (bit 5) indicates support for IGMP + version 3. + + * 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. + + * This EVPN route type is used to carry tenant IGMP multicast group + information. The Flags field assists in distributing the IGMP + Membership Report of a given host for a given multicast route. + The version bits help associate the IGMP version of receivers + participating within the EVPN domain. + + * The IE bit helps in creating filters for a given multicast route. + + * If the 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 routes, the 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. + + * Reserved bits MUST be set to 0 by the sender, and the 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 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 per the procedure defined in + [RFC7432]. + + The Multicast Source Length MUST be set to the 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) Membership Report, this field + is not used. + + The Multicast Group Length MUST be set to the length of the 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. + + 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 the router + originating this route. The SMET Originator Router IP address MUST + match that of the IMET (or S-PMSI Authentic Data (AD)) route + originated for the same EVI by the same downstream PE. + + The Flags field indicates the version of IGMP from which the + Membership Report was received. It also indicates whether the + multicast group had the Include/Exclude bit set. + + Reserved bits MUST be set to 0. They can be defined by other + documents in the future. + + IGMP is used to receive group membership information from hosts by + Top-of-the-Rack (ToR) switches. Upon receiving the host's expression + of interest in a particular group membership, this information is + then forwarded using the SMET route. The NLRI also keeps track of + the receiver's IGMP version and any source filtering for a given + group membership. All EVPN SMET routes are announced per EVI Route + Target extended communities (EVI-RT ECs). + +9.1.2. Reconstructing IGMP/MLD Membership Reports from the Selective + Multicast Route + + This section describes the procedures used to reconstruct IGMP/MLD + Membership Reports from the SMET route. + + * If the Multicast Group Length is 32, the route is translated to + the IGMP Membership Request. If the Multicast Group Length is + 128, the route is translated to an MLD Membership Request. + + * The Multicast Group Address field is translated to the IGMP/MLD + group address. + + * If the Multicast Source Length is set to 0, it is translated to + any source (*). If the Multicast Source Length is non-zero, the + Multicast Source Address field is translated to the IGMP/MLD + source address. + + * If flag bit 7 is set, it translates the Membership Report to be + IGMPv1 or MLDv1. + + * If flag bit 6 is set, it translates the Membership Report to be + IGMPv2 or MLDv2. + + * Flag bit 5 is only valid for the IGMP Membership Report; if it is + set, it translates to the IGMPv3 report. + + * If the IE flag is set, it translates to the IGMP/MLD Exclude mode + Membership Report. If the IE flag is not set (0), it translates + to the Include mode Membership Report. + +9.1.3. Default Selective Multicast Route + + If there is a multicast router connected behind the EVPN domain, the + PE MAY originate a default SMET (*,*) to get all multicast traffic in + the domain. + + +--------------+ + | | + | | + | | +----+ + | | | |---- H1(*,G1)v2 + | IP/MPLS | | PE1|---- H2(S2,G2)v3 + | Network | | |---- S2 + | | | | + | | +----+ + | | + +----+ | | + +----+ | | | | + | | S1 ---| PE2| | | + |PIM |----R1 ---| | | | + |ASM | +----+ | | + | | | | + +----+ +--------------+ + + Figure 2: Multicast Router behind the EVPN Domain + + Consider the EVPN network in 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 Rendezvous Point (RP). If + receivers behind the 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 domain. To generate wildcard (*,*) routes, the procedure + from [RFC6625] MUST be used. + +9.2. Multicast Membership Report Synch Route + + This EVPN route type is used to coordinate the 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 the 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 + 1-octet Flags field, whose fields are defined as follows: + + 0 1 2 3 4 5 6 7 + +--+--+--+--+--+--+--+--+ + | reserved |IE|v3|v2|v1| + +--+--+--+--+--+--+--+--+ + + * The least significant bit (bit 7) indicates support for IGMP + version 1. + + * The second least significant bit (bit 6) indicates support for + IGMP version 2. + + * The third least significant bit (bit 5) indicates support for IGMP + version 3. + + * 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. + + * Reserved bits MUST be set to 0. + + The Flags field assists in distributing the IGMP Membership Report of + a given host for a given multicast route. The version bits help + associate the IGMP version of receivers participating within the EVPN + domain. The Include/Exclude bit helps in creating filters for a + given multicast route. + + If the 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 the IPv6 route, the third least significant bit MUST be + 0. In case of the 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 Flags + Extended Community for the EVIs corresponding to its multihomed ESs. + + An IGMP Membership Report Synch route MUST carry exactly one ES- + Import Route Target extended community, i.e., the one that + corresponds to the ES on which the IGMP Membership Report was + received. It MUST also carry exactly one EVI-RT EC, i.e., 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 RD SHOULD be Type 1 [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 the procedure defined in + [RFC7432]. + + The Multicast Source Length MUST be set to the length of the + 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 the length of the 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 the router + originating the prefix. + + The Flags field indicates the version of IGMP from which the + Membership Report was received. It also indicates whether the + multicast group had the Include/Exclude bit set. + + Reserved bits MUST be set to 0. + +9.2.2. Reconstructing IGMP/MLD Membership Reports from a Multicast + Membership Report Synch Route + + This section describes the procedures used to reconstruct IGMP/MLD + Membership Reports from the Multicast Membership Report Synch route. + + * If the Multicast Group Length is 32, the route is translated to + the IGMP Membership Request. If the Multicast Group Length is + 128, the route is translated to an MLD Membership Request. + + * The Multicast Group Address field is translated to the IGMP/MLD + group address. + + * If the Multicast Source Length is set to 0, it is translated to + any source (*). If the Multicast Source Length is non-zero, the + Multicast Source Address field is translated to the IGMP/MLD + source address. + + * If flag bit 7 is set, it translates the Membership Report to be + IGMPv1 or MLDv1. + + * If flag bit 6 is set, it translates the Membership Report to be + IGMPv2 or MLDv2. + + * Flag bit 5 is only valid for the IGMP Membership Report; if it is + set, it translates to the IGMPv3 report. + + * If the IE flag is set, it translates to the IGMP/MLD Exclude mode + Membership Report. If the IE flag is not set (0), it translates + to the Include mode Membership Report. + +9.3. Multicast Leave Synch Route + + This EVPN route type is used to coordinate the IGMP Leave Group (x,G) + state for a given BD between the PEs attached to a given ES operating + in an All-Active (or Single-Active) redundancy mode, and it consists + of the 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) | + +--------------------------------------------------+ + | Reserved (4 octets) | + +--------------------------------------------------+ + | 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 1-octet Flags fields, which are + defined as follows: + + 0 1 2 3 4 5 6 7 + +--+--+--+--+--+--+--+--+ + | reserved |IE|v3|v2|v1| + +--+--+--+--+--+--+--+--+ + + * The least significant bit (bit 7) indicates support for IGMP + version 1. + + * The second least significant bit (bit 6) indicates support for + IGMP version 2. + + * The third least significant bit (bit 5) indicates support for IGMP + version 3. + + * 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. + + * Reserved bits MUST be set to 0. They can be defined by other + documents in the future. + + The Flags field assists in distributing the IGMP Membership Report of + a given host for a given multicast route. The version bits help + associate the IGMP version of the receivers participating within the + EVPN domain. The Include/Exclude bit helps in creating filters for a + given multicast route. + + If the 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 the IPv6 route, the third least significant bit MUST be + 0. In case of the IPv6 route, the fourth least significant bit MUST + be ignored if bit 6 is not set. + + Reserved bits in the flag MUST be set to 0. They can be defined by + other documents in the future. + +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 the Multicast Flags Extended Community for + the EVIs corresponding to its multihomed Ethernet segments. + + An IGMP Leave Synch route MUST carry exactly one ES-Import Route + Target extended community, i.e., the one that corresponds to the ES + on which the IGMP Leave was received. It MUST also carry exactly one + EVI-RT EC, i.e., 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 RD SHOULD be Type 1 [RFC4364]. The value field comprises an IP + address of the PE (typically, the loopback address), followed by a + number unique to the PE. + + The ESI MUST be set to the 10-octet value defined for the ES. + + The Ethernet Tag ID MUST be set, as per the procedure defined in + [RFC7432]. + + The Multicast Source Length MUST be set to the length of the + 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 the length of the 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 the router + originating the prefix. + + The Reserved field is not part of the route key. The originator MUST + set the Reserved field to 0; the receiver SHOULD ignore it, and if it + needs to be propagated, it MUST propagate it unchanged. + + The Maximum Response Time is the value to be used while sending a + query, as defined in [RFC2236]. + + The Flags field indicates the version of IGMP from which the + Membership Report was received. It also indicates whether the + multicast group had an Include/Exclude bit set. + +9.3.2. Reconstructing IGMP/MLD Leave from a Multicast Leave Synch Route + + This section describes the procedures used to reconstruct IGMP/MLD + Leave from the Multicast Leave Synch route. + + * If the Multicast Group Length is 32, the route is translated to + IGMP Leave. If the Multicast Group Length is 128, the route is + translated to MLD Leave. + + * The Multicast Group Address field is translated to an IGMP/MLD + group address. + + * If the Multicast Source Length is set to 0, it is translated to + any source (*). If the Multicast Source Length is non-zero, the + Multicast Source Address field is translated to the IGMP/MLD + source address. + + * If flag bit 7 is set, it translates the Membership Report to be + IGMPv1 or MLDv1. + + * If flag bit 6 is set, it translates the Membership Report to be + IGMPv2 or MLDv2. + + * Flag bit 5 is only valid for the IGMP Membership Report; if it is + set, it translates to the IGMPv3 report. + + * If the IE flag is set, it translates to the IGMP/MLD Exclude mode + Leave. If the IE flag is not set (0), it translates to the + Include mode Leave. + +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 Value of 0x06. IANA has assigned 0x09 to + Multicast Flags Extended Community in the "EVPN Extended Community + Sub-Types" subregistry. + + A PE that supports IGMP and/or the MLD Proxy on a given BD MUST + attach this extended community to the IMET route it advertises for + that BD, and it MUST set the IGMP and/or MLD Proxy Support flags to + 1. Note that a PE compliant with [RFC7432] will not advertise this + extended community, so its absence indicates that the advertising PE + does not support either IGMP or MLD Proxies. + + The advertisement of this extended community enables a more efficient + multicast tunnel setup from the source PE specially for ingress + replication, i.e., if an egress PE supports the 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: + + 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 (least significant) 2 bits are defined as the "IGMP + Proxy Support" and "MLD Proxy Support" bits (see Section 12.3. The + absence of this extended community also means that the PE does not + support the IGMP Proxy, where: + + * The Type is 0x06, as registered with IANA for EVPN Extended + Communities. + + * The Sub-Type is 0x09. + + * Flags are 2-octet values. + + - Bit 15 (shown as I) defines IGMP Proxy Support. The value of 1 + for bit 15 means that the PE supports the IGMP Proxy. The + value of 0 for bit 15 means that the PE does not support the + IGMP Proxy. + + - Bit 14 (shown as M) defines MLD Proxy Support. The value of 1 + for bit 14 means that the PE supports the MLD Proxy. The value + of 0 for bit 14 means that the PE does not support the MLD + Proxy. + + - Bits 0 to 13 are reserved for the future. The sender MUST set + it to 0, and the receiver MUST ignore it. + + * Reserved bits are set to 0. The sender MUST set it to 0, and the + receiver MUST ignore it. + + If a router does not support this specification, it MUST NOT add the + Multicast Flags Extended Community in the BGP route. When a router + receives a BGP update, if both M and I flags are 0, the router MUST + treat this update as malformed. The receiver of such an update MUST + ignore the extended community. + +9.5. EVI-RT Extended Community + + In EVPN, every EVI is associated with one or more Route Targets. + These RTs serve two functions: + + 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 ECs that can be used to identify the + EVI with which a route is associated but do not have any effect on + the distribution of the route. These new ECs are known as "Type 0 + EVI-RT EC", "Type 1 EVI-RT EC", "Type 2 EVI-RT EC", and "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: + + * 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. + + * 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. + + * If RT1 is a Transitive Four-Octet AS-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. + + * 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 per [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.) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + The value of "n" is 0x0A, 0x0B, 0x0C, or 0x0D, corresponding to EVI- + RT types 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 this situation, the RT that corresponds to a particular + EVI may be different in each AS. If a route is propagated from AS1 + to AS2, an ASBR at the AS1/AS2 border may be configured with a policy + that replaces the EVI RTs for AS1 with the corresponding EVI RTs for + AS2. This is known as RT-rewriting. + + If an ASBR is configured to perform RT-rewriting of the EVI RTs in + EVPN routes, it MUST be configured to perform RT-rewriting of the + corresponding EVI-RT extended communities in IGMP Join Synch and IGMP + Leave Synch Routes. + +9.7. BGP Error Handling + + If a received BGP update contains Flags not in accordance with the + IGMP/MLD version-X expectation, the PE MUST apply the "treat-as- + withdraw" procedure per [RFC7606]. + + If a received BGP update is malformed such that BGP route keys cannot + be extracted, then the BGP update MUST be considered invalid. The + receiving PE MUST apply the "session reset" procedure per [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 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 substrates 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], IGMPv3 [RFC3376], MLD [RFC2710], or MLDv2 [RFC3810] apply. + +12. IANA Considerations + +12.1. EVPN Extended Community Sub-Types Registration + + IANA has allocated the following codepoints in the "EVPN Extended + Community Sub-Types" subregistry under the "Border Gateway Protocol + (BGP) Extended Communities" registry. + + +================+====================================+===========+ + | Sub-Type Value | Name | Reference | + +================+====================================+===========+ + | 0x09 | Multicast Flags Extended Community | RFC 9251 | + +----------------+------------------------------------+-----------+ + | 0x0A | EVI-RT Type 0 | RFC 9251 | + +----------------+------------------------------------+-----------+ + | 0x0B | EVI-RT Type 1 | RFC 9251 | + +----------------+------------------------------------+-----------+ + | 0x0C | EVI-RT Type 2 | RFC 9251 | + +----------------+------------------------------------+-----------+ + | 0x0D | EVI-RT Type 3 | RFC 9251 | + +----------------+------------------------------------+-----------+ + + Table 1: EVPN Extended Community Sub-Types Subregistry + Allocated Codepoints + +12.2. EVPN Route Types Registration + + IANA has allocated the following EVPN route types in the "EVPN Route + Types" subregistry. + + 6 - Selective Multicast Ethernet Tag Route + + 7 - Multicast Membership Report Synch Route + + 8 - Multicast Leave Synch Route + +12.3. Multicast Flags Extended Community Registry + + IANA has created and now maintains a new subregistry called + "Multicast Flags Extended Community" under the "Border Gateway + Protocol (BGP) Extended Communities" registry. The registration + procedure is First Come First Served [RFC8126]. For the 16-bit Flags + field, the bits are numbered 0-15, from high order to low order. The + registry was initialized as follows: + + +======+====================+===========+===================+ + | Bit | Name | Reference | Change Controller | + +======+====================+===========+===================+ + | 0-13 | Unassigned | | | + +------+--------------------+-----------+-------------------+ + | 14 | MLD Proxy Support | RFC 9251 | IETF | + +------+--------------------+-----------+-------------------+ + | 15 | IGMP Proxy Support | RFC 9251 | IETF | + +------+--------------------+-----------+-------------------+ + + Table 2: Multicast Flags Extended Community + +13. References + +13.1. 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>. + + [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>. + +13.2. Informative References + + [EVPN-BUM] Zhang, Z., Lin, W., Rabadan, J., Patel, K., and A. + Sajassi, "Updates on EVPN BUM Procedures", Work in + Progress, Internet-Draft, draft-ietf-bess-evpn-bum- + procedure-updates-14, 18 November 2021, + <https://datatracker.ietf.org/doc/html/draft-ietf-bess- + evpn-bum-procedure-updates-14>. + + [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>. + + [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for + Writing an IANA Considerations Section in RFCs", BCP 26, + RFC 8126, DOI 10.17487/RFC8126, June 2017, + <https://www.rfc-editor.org/info/rfc8126>. + +Acknowledgements + + The authors would like to thank Stephane Litkowski, Jorge Rabadan, + Anoop Ghanwani, Jeffrey Haas, Krishna Muddenahally Ananthamurthy, and + Swadesh Agrawal for their reviews and valuable comments. + +Contributors + + Derek Yeung + Arrcus + Email: derek@arrcus.com + + +Authors' Addresses + + Ali Sajassi + Cisco Systems + 821 Alder Drive + Milpitas, CA 95035 + United States of America + Email: sajassi@cisco.com + + + Samir Thoria + Cisco Systems + 821 Alder Drive + Milpitas, CA 95035 + United States of America + Email: sthoria@cisco.com + + + Mankamana Mishra + Cisco Systems + 821 Alder Drive + Milpitas, CA 95035 + United States of America + Email: mankamis@cisco.com + + + Keyur Patel + Arrcus + United States of America + Email: keyur@arrcus.com + + + John Drake + Juniper Networks + Email: jdrake@juniper.net + + + Wen Lin + Juniper Networks + Email: wlin@juniper.net |