Signal-Free Locator/ID Separation Protocol (LISP) Multicast
draft-ietf-lisp-rfc8378bis-05

Network Working Group V. Moreno
Internet-Draft Google LLC
Obsoletes: 8378 (if approved) D. Farinacci
Intended status: Standards Track lispers.net
Expires: 4 June 2026 V. Govindan
 Cisco
 1 December 2025
 Signal-Free Locator/ID Separation Protocol (LISP) Multicast
 draft-ietf-lisp-rfc8378bis-05
Abstract
 This document describes the design for inter-domain multicast
 overlays using the Locator/ID Separation Protocol (LISP). The
 document specifies how LISP multicast overlays operate over a unicast
 underlays.
 When multicast sources and receivers are active at Locator/ID
 Separation Protocol (LISP) sites, the core network is required to use
 native multicast so packets can be delivered from sources to group
 members. When multicast is not available to connect the multicast
 sites together, a signal-free mechanism can be used to allow traffic
 to flow between sites. The mechanism within here uses unicast
 replication and encapsulation over the core network for the data
 plane and uses the LISP mapping database system so encapsulators at
 the source LISP multicast site can find decapsulators at the receiver
 LISP multicast sites.
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
 Task Force (IETF). Note that other groups may also distribute
 working documents as Internet-Drafts. The list of current Internet-
 Drafts is at https://datatracker.ietf.org/drafts/current/.
 Internet-Drafts are draft documents valid for a maximum of six months
 and may be updated, replaced, or obsoleted by other documents at any
 time. It is inappropriate to use Internet-Drafts as reference
 material or to cite them other than as "work in progress."
 This Internet-Draft will expire on 4 June 2026.
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Copyright Notice
 Copyright (c) 2025 IETF Trust and the persons identified as the
 document authors. All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 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
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Table of Contents
 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
 2.1. Definition of Terms . . . . . . . . . . . . . . . . . . . 4
 2.2. Requirements Language . . . . . . . . . . . . . . . . . . 6
 3. Reference Model . . . . . . . . . . . . . . . . . . . . . . . 6
 4. General Procedures . . . . . . . . . . . . . . . . . . . . . 7
 4.1. General Receiver-Site Procedures . . . . . . . . . . . . 8
 4.1.1. Multicast Receiver Detection . . . . . . . . . . . . 8
 4.1.2. Receiver-Site Registration . . . . . . . . . . . . . 9
 4.1.3. Consolidation of the Replication List . . . . . . . . 10
 4.2. General Source-Site Procedures . . . . . . . . . . . . . 10
 4.2.1. Multicast Tree Building at the Source Site . . . . . 10
 4.2.2. Multicast Destination Resolution . . . . . . . . . . 11
 4.3. General LISP Notification Procedures . . . . . . . . . . 11
 5. Source-Specific Multicast Trees . . . . . . . . . . . . . . . 12
 5.1. Source Directly Connected to Source-ITRs . . . . . . . . 12
 5.2. Source Not Directly Connected to Source-ITRs . . . . . . 12
 6. Multihoming Considerations . . . . . . . . . . . . . . . . . 12
 6.1. Multiple ITRs at a Source Site . . . . . . . . . . . . . 13
 6.2. Multiple ETRs at a Receiver Site . . . . . . . . . . . . 13
 6.3. Multiple RLOCs for an ETR at a Receiver Site . . . . . . 14
 6.4. Multicast RLOCs for an ETR at a Receiver Site . . . . . . 14
 7. PIM Any-Source Multicast Trees . . . . . . . . . . . . . . . 15
 8. Signal-Free Multicast for Replication Engineering . . . . . . 16
 9. Security Considerations . . . . . . . . . . . . . . . . . . . 18
 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
 11.1. Normative References . . . . . . . . . . . . . . . . . . 19
 11.2. Informative References . . . . . . . . . . . . . . . . . 20
 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 21
 Appendix B. Document Change Log . . . . . . . . . . . . . . . . 21
 B.1. Changes to draft-ietf-lisp-rfc8378bis-05 . . . . . . . . 21
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 B.2. Changes to draft-ietf-lisp-rfc8378bis-04 . . . . . . . . 21
 B.3. Changes to draft-ietf-lisp-rfc8378bis-03 . . . . . . . . 21
 B.4. Changes to draft-ietf-lisp-rfc8378bis-00/01/02 . . . . . 22
 B.5. Changes to draft-ietf-lisp-rfc8378bis-00 . . . . . . . . 22
 B.6. Changes to draft-farinacci-lisp-rfc8378bis-00 . . . . . . 23
 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction
 When multicast sources and receivers are active at LISP sites, and
 the core network between the sites does not provide multicast
 support, a signal-free mechanism can be used to create an overlay
 that will allow multicast traffic to flow between sites and connect
 the multicast trees at the different sites.
 The signal-free mechanism proposed here does not extend PIM [RFC7761]
 over the overlay as proposed in [I-D.ietf-lisp-rfc6831bis], nor does
 the mechanism utilize direct signaling between the Receiver-ETRs and
 Sender-ITRs as described in [LISP-MULTI-SIGNALING]. The signal-free
 mechanism proposed reduces the amount of signaling required between
 sites to a minimum and is centered around the registration of
 receiver sites for a particular multicast group or multicast channel
 with the LISP mapping system.
 Registrations from the different receiver sites will be merged at the
 mapping system to assemble a multicast-replication-list inclusive of
 all Routing Locators (RLOCs) that lead to receivers for a particular
 multicast group or multicast channel. The replication list for each
 specific multicast entry is maintained as a database mapping entry in
 the LISP mapping system.
 When the Ingress Tunnel Router (ITR) at the source site receives
 multicast traffic from sources at its site, the ITR can query the
 mapping system by issuing Map-Request messages for the (S,G) source
 and destination addresses in the packets received. The mapping
 system will return the RLOC replication list to the ITR, which the
 ITR will cache as per standard LISP procedure. Since the core is
 assumed to not support multicast, the ITR will replicate the
 multicast traffic for each RLOC on the replication list and will
 unicast encapsulate the traffic to each RLOC. The combined function
 or replicating and encapsulating the traffic to the RLOCs in the
 replication list is referred to as "rep-encapsulation" in this
 document.
 The document describes general procedures (Section 4) and information
 encoding that are required at the receiver sites and source sites to
 achieve signal-free multicast interconnectivity. The general
 procedures for mapping system notifications to different sites are
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 also described. A section dedicated to the specific case of Source-
 Specific Multicast (SSM) trees discusses the implications to the
 general procedures for SSM multicast trees over different topological
 scenarios. A section on Any-Source Multicast (ASM) support is
 included to identify the constraints that come along with supporting
 it using LISP signal-free multicast.
 There is a section dedicated to Replication Engineering, which is a
 mechanism to reduce the impact of head-end replication. The mapping
 system, via LISP signal-free mechanisms, can be used to build a layer
 of Re-encapsulating Tunnel Routers (RTRs).
2. Terminology
2.1. Definition of Terms
 LISP-related terms, notably Map-Request, Map-Reply, Ingress Tunnel
 Router (ITR), Egress Tunnel Router (ETR), Map-Server (MS), and
 Map-Resolver (MR) are defined in the LISP specification [RFC9300].
 Extensions to the definitions in [RFC9300] for their application to
 multicast routing are documented in [I-D.ietf-lisp-rfc6831bis].
 Terms defining interactions with the LISP mapping system are defined
 in [RFC9301].
 The following terms are consistent with the definitions in [RFC9300]
 and [I-D.ietf-lisp-rfc6831bis]. The terms are specific cases of the
 general terms and are defined here to facilitate the descriptions and
 discussions within this particular document.
 Source: Multicast source endpoint. The host that originates
 multicast packets.
 Receiver: Multicast group member endpoint. The host joins a
 multicast group as a receiver of multicast packets sent to the group.
 Receiver site: LISP site where multicast receivers are located.
 Source site: LISP site where multicast sources are located.
 RP site: LISP site where an ASM PIM Rendezvous Point (RP) [RFC7761]
 is located. The RP site and the source site MAY be the same in some
 deployments.
 Receiver-ETR: LISP decapsulating the Tunnel Router (xTR) at the
 receiver site. This is a multicast ETR.
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 Source-ITR: LISP encapsulating xTR at the source site. This is a
 multicast ITR.
 RP-xTR: LISP xTR at the RP site. This is typically a multicast ITR.
 Replication List (RL): Mapping-entry containing the list of RLOCs
 that have registered receivers for a particular multicast entry.
 Replication List Entry (RLE): A LISP Canonical Address Format (LCAF)
 Type detailed in [RFC8060] that describes an overlay distribution
 tree as a list of xTRs with associated level values. Each entry in
 the replication list contains an address of an xTR and an RTR level
 value.
 Overlay Distribution Tree: A degree-constrained spanning tree that
 represents the path followed by unicast and/or multicast encapsulated
 multicast packets from the root (ITR) to the leaves (ETRs) through
 intermediary nodes (RTRs). The ITR and RTRs unicast and/or multicast
 replicate packets to their tree children.
 Multicast entry: A tuple identifying a multicast tree. Multicast
 entries are in the form of (S-prefix, G-prefix).
 Rep-encapsulation: The process of replicating and then encapsulating
 traffic to multiple RLOCs.
 Re-encapsulating Tunnel Router (RTR): An RTR is a router that
 implements the re-encapsulating tunnel function detailed in Section 8
 of the main LISP specification [RFC9300].
 RTR Level: An RTR level is encoded in a Replication List Entry (RLE)
 LISP Canonical Address Format (LCAF) Type detailed in [RFC8060].
 Each entry in the replication list contains an address of an xTR and
 a level value. Level values are used to create a replication
 hierarchy so that ITRs at source LISP sites replicate to the lowest
 (smaller value) level number RTRs in an RLE. And then RTRs at a
 given level replicate to the next higher level of RTRs. The number
 of RTRs at each level are engineered to control the fan-out or
 replication factor, so a trade-off between the width of the level
 versus the number of levels can be selected.
 ASM: Any-Source Multicast as defined in [RFC3569] where multicast
 distribution trees are built with a Rendezvous Point [RFC7761].
 SSM: Source-Specific Multicast as defined in [RFC3569] where
 multicast distribution trees are built and rooted at the multicast
 router(s) directly connected to the multicast source.
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2.2. Requirements Language
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
 "OPTIONAL" in this document are to be interpreted as described in BCP
 14 [RFC2119] [RFC8174] when, and only when, they appear in all
 capitals, as shown here.
3. Reference Model
 The reference model that will be used for the discussion of the
 signal-free multicast tree interconnection is illustrated in
 Figure 1.
 +-----+
 |MS/MR|
 +---+ +---+ +-----+ +---+ +---+
 Src-1 ----| R1|-----|ITR| | |ETR|------| R2|----- Rcv-2
 +---+ +---+ | +---+ +---+
 \ | /
 Source-site-1 \ | / Receiver-site-2
 \ | /
 \ | /
 \ | /
 Core
 / \
 / \
 / \
 / \
 / \
 +---+ +---+
 Src-3 --------------|ITR| |ETR|---------------- Rcv-4
 +---+ +---+
 Source-site-3 Receiver-site-4
 Figure 1: LISP Multicast Generic Reference Model
 Sites 1 and 3 are source sites.
 Source-site-3 presents a source (Src-3) that is directly connected to
 the Source-ITR.
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 Source-site-1 presents a source (Src-1) that is one hop or more away
 from the Source-ITR.
 Receiver-site-2 and -4 are receiver sites with not-directly connected
 and directly connected receiver endpoints, respectively.
 R1 is a multicast router in Source-site-1.
 R2 is a multicast router at the Receiver-site-2.
 Map-Servers and Map-Resolvers are reachable in the RLOC space in the
 core; only one is shown for illustration purposes, but these can be
 many or even part of a distributed mapping system, such as a
 Delegated Database Tree (DDT) [RFC8111].
 The procedures for interconnecting multicast trees over an overlay
 can be broken down into three functional areas:
 * Receiver-site procedures
 * Source-site procedures
 * LISP notification procedures
 The receiver-site procedures will be common for most tree types and
 topologies.
 The procedures at the source site can vary depending on the type of
 trees being interconnected as well as the topological relation
 between sources and source-site xTRs. For ASM trees, a special case
 of the source site is the RP site for which a variation of the
 source-site procedures may be necessary if ASM trees are to be
 supported in future specifications of LISP signal-free multicast.
 The LISP notification procedures between sites are normalized for the
 different possible scenarios. Certain scenarios may benefit from a
 simplified notification mechanism or no notification requirement at
 all.
4. General Procedures
 The interconnection of multicast trees across different LISP sites
 involves the following procedures to build the necessary multicast
 distribution trees across sites.
 1. The presence of multicast receiver endpoints is detected by the
 Receiver-ETRs at the receiver sites.
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 2. Receiver-ETRs register their RLOCs as part of the replication
 list for the multicast entry the detected receivers subscribe to.
 3. The mapping system merges all Receiver-ETR or delivery-group
 RLOCs to build a comprehensive replication list inclusive of all
 receiver sites for each multicast entry.
 4. LISP Map-Notify messages MUST be sent to the Source-ITR informing
 of any changes in the replication list.
 5. Multicast tree building at the source site is initiated when the
 Source-ITR receives the LISP notification.
 Once the multicast distribution trees are built, the following
 forwarding procedures may take place:
 1. The source sends multicast packets to the multicast group
 destination address.
 2. Multicast traffic follows the multicast tree built at the source
 site and makes its way to the Source-ITRs.
 3. The Source-ITR will issue a Map-Request to resolve the
 replication list for the multicast entry.
 4. The mapping system responds to the Source-ITR with a Map-Reply
 containing the replication list for the multicast group
 requested.
 5. The Source-ITR caches the replication list received in the
 map-reply for the multicast entry.
 6. Multicast traffic is rep-encapsulated. That is, the packet is
 replicated for each RLOC in the replication list and then
 encapsulated to each one.
4.1. General Receiver-Site Procedures
4.1.1. Multicast Receiver Detection
 When the Receiver-ETRs are directly connected to the receivers (e.g.,
 Receiver-site-4 in Figure 1), the Receiver-ETRs will receive IGMP
 reports from the receivers indicating which group the receivers wish
 to subscribe to. Based on these IGMP reports, the Receiver-ETR is
 made aware of the presence of receivers as well as which group they
 are interested in.
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 When the Receiver-ETRs are several hops away from the receivers
 (e.g., Receiver-site-2 in Figure 1), the Receiver-ETRs will receive
 PIM join messages, which will allow the Receiver-ETR to know that
 there are multicast receivers at the site and also to learn which
 multicast group the receivers are for.
4.1.2. Receiver-Site Registration
 Once the Receiver-ETRs detect the presence of receivers at the
 receiver site, the Receiver-ETRs MUST issue Map-Register messages to
 include the Receiver-ETR RLOCs in the replication list for the
 multicast entry the receivers joined.
 The Map-Register message MUST use the multicast entry (Source, Group)
 tuple as its Endpoint ID (EID) record type with the Receiver-ETR
 RLOCs conforming the locator set.
 The EID in the Map-Register message MUST be encoded using the
 Multicast Info LCAF Type defined in [RFC8060].
 The RLOC in the Map-Register message MUST be encoded using the RLE
 LCAF Type defined in [RFC8060] with the Level Value fields for all
 entries set to 128 (decimal).
 The encoding described above MUST be used consistently for Map-
 Register messages, entries in the mapping system, Map-Reply messages,
 as well as the EID-to-RLOC Map-Cache at the Source-ITRs.
 The Map-Register messages [RFC9301] sent by the Receiver-ETRs MUST
 have the following bits set as specified here:
 1. merge-request bit set to 1. The Map-Register messages are sent
 with "Merge Semantics". The Map-Server will receive
 registrations from a multitude of Receiver-ETRs. The Map-Server
 will merge the registrations for common EIDs and maintain a
 consolidated replication list for each multicast entry.
 2. want-map-notify bit (M) set to 0. This tells the mapping system
 that the Receiver-ETR does not expect to receive Map-Notify
 messages as it does not need to be notified of all changes to the
 replication list.
 3. proxy-reply bit (P) set to 1. The merged replication list is
 kept in the Map-Servers. By setting the proxy-reply bit, the
 Receiver-ETRs instruct the mapping system to proxy reply to Map-
 Requests issued for the multicast entries.
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 Map-Register messages for a particular multicast entry MAY be sent
 for every receiver detected, even if previous receivers have been
 detected for the particular multicast entry. This allows the
 replication list to remain up to date.
 Receiver-ETRs MUST be configured to know what Map-Servers Map-
 Register messages are sent to. The configuration is likely to be
 associated with an S-prefix that multiple (S,G) entries match to and
 are more specific for. Therefore, the S-prefix determines the Map-
 Server set in the least number of configuration statements.
4.1.3. Consolidation of the Replication List
 The Map-Server will receive registrations from a multitude of
 Receiver-ETRs. The Map-Server will merge the registrations for
 common EIDs and consolidate a replication list for each multicast
 entry.
 When an ETR sends an RLE RLOC-record in a Map-Register and the RLE
 already exists in the Map-Server's RLE-merged list, the Map-Server
 will replace the single RLE with the information from the Map-
 Register RLOC-record. The Map-Server MUST NOT merge duplicate RLOCs
 in the consolidated replication list.
4.2. General Source-Site Procedures
 Source-ITRs MUST register the unicast EIDs of any sources or
 Rendezvous Points that may be present on the source site. In other
 words, it is assumed that the sources and RPs are LISP EIDs.
 The registration of the unicast EIDs for the sources or Rendezvous
 Points allows the Map-Server to know where to send Map-Notify
 messages to. Therefore, the Source-ITR MUST register the unicast
 S-prefix EID with the want-map-notify bit set in order to receive
 Map-Notify messages whenever there is a change in the replication
 list.
4.2.1. Multicast Tree Building at the Source Site
 When the source site receives the Map-Notify messages from the
 mapping system as described in Section 4.3, it will initiate the
 process of building a multicast distribution tree that will allow the
 multicast packets from the source to reach the Source-ITR.
 The Source-ITR MUST issue a PIM join for the multicast entry for
 which it received the Map-Notify message. The join will be issued in
 the direction of the source or in the direction of the RP for the SSM
 and ASM cases, respectively.
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4.2.2. Multicast Destination Resolution
 On reception of multicast packets, the Source-ITR obtains the
 replication list for the (S,G) addresses in the packets.
 In order to obtain the replication list, the Source-ITR MUST issue a
 Map-Request message in which the EID is the (S,G) multicast tuple,
 which is encoded using the Multicast Info LCAF Type defined in
 [RFC8060].
 The mapping system (most likely the Map-Server) will Map-Reply with
 the merged replication list maintained in the mapping system. The
 Map-Reply message MUST follow the format defined in [RFC9301]; its
 EID is encoded using the Multicast Info LCAF Type, and the
 corresponding RLOC-records are encoded using the RLE LCAF Type. Both
 LCAF Types are defined in [RFC8060].
4.3. General LISP Notification Procedures
 The Map-Server will issue LISP Map-Notify messages to inform the
 source site of the presence of receivers for a particular multicast
 group over the overlay.
 Updated Map-Notify messages SHOULD be issued every time a new
 registration is received from a receiver site. This guarantees that
 the source sites are aware of any potential changes in the multicast-
 distribution-list membership.
 The Map-Notify messages carry (S,G) multicast EIDs encoded using the
 Multicast Info LCAF Type defined in [RFC8060].
 Map-Notify messages will be sent by the Map-Server to the RLOCs with
 which the unicast S-prefix EID was registered. In the case when
 sources are discovered dynamically [LISP-EID-MOBILITY], xTRs MUST
 register sources explicitly with the want-map-notify bit set. This
 is so the ITR in the site the source has moved to can get the most
 current replication list.
 When both the receiver sites and the source sites register to the
 same Map-Server, the Map-Server has all the necessary information to
 send the Map-Notify messages to the source site.
 When the Map-Servers are distributed (when using LISP-DDT [RFC8111]),
 the receiver sites may register to one Map-Server while the source
 site registers to a different Map-Server. In this scenario, the Map-
 Server for the receiver sites MUST resolve the unicast S-prefix EID
 across a distributed mapping transport system, per standard LISP
 lookup procedures, and obtain the necessary information to send the
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 Map-Notify messages to the source site. The Map-Notify messages are
 sent with an authentication length of 0 as they would not be
 authenticated.
 When the Map-Servers are distributed, different receiver sites may
 register to different Map-Servers. However, this is not supported
 with the currently defined mechanisms.
5. Source-Specific Multicast Trees
 The interconnection of SSM trees across sites will follow the general
 receiver-site procedures described in Section 4.1 on the receiver
 sites.
 The source-site procedures will vary depending on the topological
 location of the source within the source site as described in
 Sections 5.1 and 5.2.
5.1. Source Directly Connected to Source-ITRs
 When the source is directly connected to the Source-ITR, it is not
 necessary to trigger signaling to build a local multicast tree at the
 source site. Therefore Map-Notify messages are not required to
 initiate building of the multicast tree at the source site.
 Map-Notify messages are still required to ensure that any changes to
 the replication list are communicated to the source site so that the
 map-cache at the Source-ITRs is kept updated.
5.2. Source Not Directly Connected to Source-ITRs
 The general LISP notification procedures described in Section 4.3
 MUST be followed when the source is not directly connected to the
 Source-ITR. On reception of Map-Notify messages, local multicast
 signaling MUST be initiated at the source site per the general
 source-site procedures for multicast tree building described in
 Section 4.2.1.
 In the SSM case, the IP address of the source is known, and it is
 also registered with the LISP mapping system. Thus, the mapping
 system MAY resolve the mapping for the source address in order to
 send Map-Notify messages to the correct Source-ITR.
6. Multihoming Considerations
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6.1. Multiple ITRs at a Source Site
 When multiple ITRs exist at a source multicast site, care MUST be
 taken that more than one ITR does not head-end replicate packets;
 otherwise, receiver multicast sites will receive duplicate packets.
 The following procedures will be used for each topology scenario:
 * When more than one ITR is directly connected to the source host,
 either the PIM Designated Router (DR) or the IGMP querier (when
 PIM is not enabled on the ITRs) is responsible for packet
 replication. All other ITRs silently drop the packet. In the
 IGMP querier case, one or more ITRs on the source LAN MUST be IGMP
 querier candidates. Therefore, it is REQUIRED that they be
 configured as such.
 * When more than one ITR is multiple hops away from the source host
 and one of the ITRs is the PIM Rendezvous Point, then the PIM RP
 is responsible for packet replication.
 * When more than one ITR is multiple hops away from the source host
 and the PIM Rendezvous Point is not one of the ITRs, then one of
 the ITRs MUST join to the RP. When a Map-Notify is received from
 the Map-Server by an ITR, only the highest RLOC addressed ITR will
 join toward the PIM RP or toward the source.
6.2. Multiple ETRs at a Receiver Site
 When multiple ETRs exist in a receiver multicast site and each one
 creates a multicast join state, each Map-Registers its RLOC address
 to the mapping system. In this scenario, the replication happens on
 the overlay causing multiple ETR entry points to replicate to all
 receivers instead of a single ETR entry point replicating to all
 receivers. If an ETR does not create join state, because it has not
 received PIM joins or IGMP reports, it will not Map-Register its RLOC
 addresses to the mapping system. The same procedures in Section 4.1
 are followed.
 When multiple ETRs exist on the same LAN as a receiver host, then the
 PIM DR (when PIM is enabled) or the IGMP querier is responsible for
 sending a Map-Register for its RLOC. In the IGMP case, one or more
 ETRs on a LAN MUST be IGMP querier candidates. Therefore, it is
 REQUIRED that they be configured as such.
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6.3. Multiple RLOCs for an ETR at a Receiver Site
 It may be desirable to have multiple underlay paths to an ETR for
 multicast packet delivery. This can be done by having multiple RLOCs
 assigned to an ETR and having the ETR send Map-Registers for all its
 RLOCs. By doing this, an ITR can choose a specific path based on
 underlay performance and/or RLOC reachability.
 It is recommended that an ETR send a Map-Register with a single RLOC-
 record that uses the Explicit Locator Path (ELP) LCAF Type [RFC8060]
 that is nested inside the RLE LCAF. For example, say ETR1 has
 assigned RLOC1 and RLOC2 for a LISP receiver site. Also, there is
 ETR2 in another LISP receiver site that has RLOC3. The two receiver
 sites have the same (S,G) being joined. Here is how the RLOC-record
 is encoded on each ETR:
 ETR1: EID-record: (S,G)
 RLOC-record: RLE[ ELP{ (RLOC1,s,p), (RLOC2,s,p) } ]
 ETR2: EID-record: (S,G)
 RLOC-record: RLE[ RLOC3 ]
 And here is how the entry is merged and stored on the Map-Server
 since the Map-Registers have an RLE-encoded RLOC-record:
 MS: EID-record: (S,G)
 RLOC-record: RLE[ RLOC3, ELP{ (RLOC1,s,p), (RLOC2,s,p) } ]
 When the ITR receives a packet from a multicast source S for group G,
 it uses the merged RLOC-record returned from the Map-Server. The ITR
 replicates the packet to (RLOC3 and RLOC1) or (RLOC3 and RLOC2).
 Since it is required for the S-bit to be set for RLOC1, the ITR MUST
 replicate to RLOC1 if it is reachable. When the required P-bit is
 also set, the RLOC-reachability mechanisms from [RFC9300] are
 followed. If the ITR determines that RLOC1 is unreachable, it uses
 RLOC2, as long as RLOC2 is reachable.
6.4. Multicast RLOCs for an ETR at a Receiver Site
 This specification is focused on underlays without multicast support,
 but it does not preclude the use of multicast RLOCs in RLEs. ETRs
 MAY register multicast EID entries using multicast RLOCs. In such
 cases, the ETRs will be joined to underlay multicast distribution
 trees by using IGMP as a multicast host using mechanisms in [RFC2236]
 and [RFC3376].
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7. PIM Any-Source Multicast Trees
 LISP signal-free multicast can support ASM trees in limited but
 acceptable topologies. It is RECOMMENDED, for the simplification of
 building ASM trees across the LISP overlay, to have PIM-ASM run
 independently in each LISP site. What this means is that a PIM RP is
 configured in each LISP site so PIM Register procedures and (*,G)
 state maintenance is contained within the LISP site.
 The following procedure will be used to support ASM in each LISP
 site:
 1. In a receiver site, the RP is co-located with the ETR. RPs for
 different groups can be spread across each ETR, but is not
 required.
 2. When (*,G) state is created in an ETR, the procedures in
 Section 4.1.2 are followed. In addition, the ETR registers
 (S-prefix,G), where S-prefix is 0/0 (the respective unicast
 default route for the address-family) to the mapping system.
 3. In a source site, the RP is co-located with the ITR. RPs for
 different groups can be spread across each ITR, but is not
 required.
 4. When a multicast source sends a packet, a PIM Register message is
 delivered to the ITR, and the procedures in Section 4.2 are
 followed.
 5. When the ITR sends a Map-Request for (S,G) and no receiver site
 has registered for (S,G), the mapping system will return the
 (0/0,G) entry to the ITR so it has a replication list of all the
 ETRs that have received (*,G) state.
 6. The ITR stores the replication list in its map-cache for (S,G).
 It replicates packets to all ETRs in the list.
 7. ETRs decapsulate packets and forward based on (*,G) state in
 their site.
 8. When last-hop PIM routers join the newly discovered (S,G), the
 ETR will store the state and follow the procedures in
 Section 4.1.2.
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8. Signal-Free Multicast for Replication Engineering
 The mechanisms in this specification can be applied to the "LISP
 Replication Engineering" [LISP-RE] design. Rather than have the
 layered LISP-RE RTR hierarchy use signaling mechanisms, the RTRs can
 register their availability for multicast tree replication via the
 mapping database system.
 As stated in [LISP-RE], the RTR-layered hierarchy is used to avoid
 head-end replication in replicating nodes closest to a multicast
 source. Rather than have multicast ITRs replicate to each ETR in an
 RLE of an (S,G) mapping database entry, it could replicate to one or
 more layer 0 RTRs in the LISP-RE hierarchy.
 This document specifies how the RTR hierarchy is determined but not
 the optimal layers of RTRs to be used. Methods for determining
 optimal paths or RTR topological closeness are out of scope for this
 document.
 There are two formats an (S,G) mapping database entry could have.
 One format is a 'complete-format', and the other is a 'filtered-
 format'. A 'complete-format' entails an (S,G) entry having multiple
 RLOC-records that contain both ETRs that have registered as well as
 the RTRs at the first level of the LISP-RE hierarchy for the ITR to
 replicate to. When using 'complete-format', the ITR has the ability
 to select if it replicates to RTRs or to the registered ETRs at the
 receiver sites. A 'filtered-format' (S,G) entry is one where the
 Map-Server returns the RLOC-records that it decides the ITR SHOULD
 use. So replication policy is shifted from the ITRs to the mapping
 system. The Map-Servers can also decide for a given ITR if it uses a
 different set of replication targets per (S,G) entry for which the
 ITR is replicating for.
 The procedure for the LISP-RE RTRs to make themselves available for
 replication can occur before or after any receivers join an (S,G)
 entry or any sources send for a particular (S,G) entry. Therefore,
 newly configured RTR state will be used to create new (S,G) state and
 will be inherited into existing (S,G) state. A set of RTRs can
 register themselves to the mapping system or a third party can do so
 on their behalf. When RTR registration occurs, it is done with an
 (S-prefix, G-prefix) entry so it can advertise its replication
 services for a wide range of source/group combinations.
 When a Map-Server receives (S,G) registrations from ETRs and
 (S-prefix, G-prefix) registrations from RTRs, it has the option of
 merging the RTR RLOC-records for each (S,G) that is more specific for
 the (S-prefix, G-prefix) entry or keeping them separate. When
 merging, a Map-Server is ready to return a 'complete-format' Map-
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 Reply. When keeping the entries separate, the Map-Server can decide
 what to include in a Map-Reply when a Map-Request is received. It
 can include a combination of RLOC-records from each entry or decide
 to use one or the other depending on policy configured.
 +---+ +----+
 Src-1 --------------|ITR| |ETR1|--------------- Rcv-1
 +---+ +----+
 \ /
 Source-site-1 \ / Receiver-site-1
 \ /
 \ /
 +----+ \ / +----+
 |RTR1| \ / |RTR2| Level-0
 +----+ \ / +----+
 \ <^^^^^^^^^^^^^^> /
 \ < > /
 < Core Network >
 < >
 <vvvvvvvvvvvvvv>
 / / \ \
 / / \ \
 +----+ / / \ \ +----+
 |RTR3| / \ |RTR4| Level-1
 +----+ / \ +----+
 / \
 / \
 +----+ +----+
 Rcv-2 --------------|ETR2| |ETR3|--------------- Rcv-3
 +----+ +----+
 Receiver-site-2 Receiver-site-3
 Figure 2: LISP-RE Reference Model
 Here is a specific example, illustrated in Figure 2, of (S,G) and
 (S-prefix, G-prefix) mapping database entries when a source S is
 behind an ITR, and there are receiver sites joined to (S,G) via ETR1,
 ETR2, and ETR3. And there exists a LISP-RE hierarchy of RTR1 and
 RTR2 at level-0 and RTR3 and RTR4 at level-1:
 EID-record: (S,G)
 RLOC-record: RLE: (ETR1, ETR2, ETR3), p1
 EID-record: (S-prefix, G-prefix)
 RLOC-record: RLE: (RTR1(L0), RTR2(L0), RTR3(L1), RTR4(L1)), p1
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 The above entries are in the form in which they were registered and
 are stored in a Map-Server. When a Map-Server uses 'complete-
 format', the Map-Reply it originates has the mapping record encoded
 as:
 EID-record: (S,G)
 RLOC-record: RLE: (RTR1(L0), RTR3(L1)), p1
 RLOC-record: RLE: (ETR1, ETR2, ETR3), p1
 The above Map-Reply allows the ITR to decide if it replicates to the
 ETRs or if it SHOULD replicate only to level-0 RTR1. This decision
 is left to the ITR since both RLOC-records have priority 1. If the
 Map-Server wanted to force the ITR to replicate to RTR1, it would set
 the ETRs RLOC-record to a priority greater than 1.
 When a Map_server uses "filtered-format', the Map-Reply it originates
 has the mapping record encoded as:
 EID-record: (S,G)
 RLOC-record: RLE: (RTR1(L0), RTR3(L1)), p1
 An (S,G) entry can contain alternate RTRs. So rather than
 replicating to multiple RTRs, one RTR set MAY be used based on the
 RTR reachability status. An ITR can test reachability status to any
 layer 0 RTR using RLOC-probing, so it can choose one RTR from a set
 to replicate to. When this is done, the RTRs are encoded in
 different RLOC-records instead of together in one RLE RLOC-record.
 This moves the replication load off the ITRs at the source site to
 the RTRs inside the network infrastructure. This mechanism can also
 be used by level-n RTRs to level-n+1 RTRs.
 The following mapping would be encoded in a Map-Reply sent by a Map-
 Server and stored in the ITR. The ITR would use RTR1 until it went
 unreachable and then switch to use RTR2:
 EID-record: (S,G)
 RLOC-record: RTR1, p1
 RLOC-record: RTR2, p2
9. Security Considerations
 The security concerns for LISP-Multicast are mainly the same as for
 the base LISP specification [RFC9300] and [RFC9301]. LISP-SEC
 [RFC9303] defines a set of security mechanisms that provide origin
 authentication, integrity, and anti-replay protection to LISP's EID-
 to-RLOC mapping data conveyed via the mapping lookup process. LISP-
 SEC also enables verification of authorization on EID-prefix claims
 in Map-Reply messages.
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 The security of the mapping system infrastructure depends on the
 particular mapping database used. As an example, [RFC8111] defines a
 public-key-based mechanism that provides origin authentication and
 integrity protection to the LISP DDT protocol.
 Map-Replies received by the Source-ITR can be signed (by the Map-
 Server), so the ITR knows the replication list is from a legitimate
 source.
 Data-plane encryption can be used when doing unicast rep-
 encapsulation as described in [RFC8061].
10. IANA Considerations
 This document has no IANA actions.
11. References
11.1. Normative References
 [I-D.ietf-lisp-rfc6831bis]
 Farinacci, D., Meyer, D., Zwiebel, J., Venaas, S., and V.
 P. Govindan, "The Locator/ID Separation Protocol (LISP)
 for Multicast Environments", Work in Progress, Internet-
 Draft, draft-ietf-lisp-rfc6831bis-05, 18 November 2025,
 <https://datatracker.ietf.org/doc/html/draft-ietf-lisp-
 rfc6831bis-05>.
 [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>.
 [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>.
 [RFC3569] Bhattacharyya, S., Ed., "An Overview of Source-Specific
 Multicast (SSM)", RFC 3569, DOI 10.17487/RFC3569, July
 2003, <https://www.rfc-editor.org/info/rfc3569>.
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 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
 Multicast - Sparse Mode (PIM-SM): Protocol Specification
 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
 2016, <https://www.rfc-editor.org/info/rfc7761>.
 [RFC8060] Farinacci, D., Meyer, D., and J. Snijders, "LISP Canonical
 Address Format (LCAF)", RFC 8060, DOI 10.17487/RFC8060,
 February 2017, <https://www.rfc-editor.org/info/rfc8060>.
 [RFC8111] Fuller, V., Lewis, D., Ermagan, V., Jain, A., and A.
 Smirnov, "Locator/ID Separation Protocol Delegated
 Database Tree (LISP-DDT)", RFC 8111, DOI 10.17487/RFC8111,
 May 2017, <https://www.rfc-editor.org/info/rfc8111>.
 [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>.
 [RFC8378] Moreno, V. and D. Farinacci, "Signal-Free Locator/ID
 Separation Protocol (LISP) Multicast", RFC 8378,
 DOI 10.17487/RFC8378, May 2018,
 <https://www.rfc-editor.org/info/rfc8378>.
 [RFC9300] Farinacci, D., Fuller, V., Meyer, D., Lewis, D., and A.
 Cabellos, Ed., "The Locator/ID Separation Protocol
 (LISP)", RFC 9300, DOI 10.17487/RFC9300, October 2022,
 <https://www.rfc-editor.org/info/rfc9300>.
 [RFC9301] Farinacci, D., Maino, F., Fuller, V., and A. Cabellos,
 Ed., "Locator/ID Separation Protocol (LISP) Control
 Plane", RFC 9301, DOI 10.17487/RFC9301, October 2022,
 <https://www.rfc-editor.org/info/rfc9301>.
 [RFC9303] Maino, F., Ermagan, V., Cabellos, A., and D. Saucez,
 "Locator/ID Separation Protocol Security (LISP-SEC)",
 RFC 9303, DOI 10.17487/RFC9303, October 2022,
 <https://www.rfc-editor.org/info/rfc9303>.
11.2. Informative References
 [LISP-EID-MOBILITY]
 Portoles-Comeras, M., Ashtaputre, V., Moreno, V., Maino,
 F., and D. Farinacci, "LISP L2/L3 EID Mobility Using a
 Unified Control Plane", Work in Progress, draft-ietf-lisp-
 eid-mobility-01, November 2017.
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 [LISP-MULTI-SIGNALING]
 Farinacci, D. and M. Napierala, "LISP Control-Plane
 Multicast Signaling", Work in Progress, draft-farinacci-
 lisp-mr-signaling-06, February 2015.
 [LISP-RE] Coras, F., Cabellos-Aparicio, A., Domingo-Pascual, J.,
 Maino, F., and D. Farinacci, "LISP Replication
 Engineering", Work in Progress, draft-coras-lisp-re-08,
 November 2015.
 [RFC8061] Farinacci, D. and B. Weis, "Locator/ID Separation Protocol
 (LISP) Data-Plane Confidentiality", RFC 8061,
 DOI 10.17487/RFC8061, February 2017,
 <https://www.rfc-editor.org/info/rfc8061>.
Appendix A. Acknowledgements
 The authors want to thank Greg Shepherd, Joel Halpern, and Sharon
 Barkai for their insightful contribution to shaping the ideas in this
 document. A special thanks to Luigi Iannone, LISP WG co-chair, for
 shepherding this working group document. Thanks also goes to Jimmy
 Kyriannis, Paul Vinciguerra, Florin Coras, and Yan Filyurin for
 testing an implementation of this document.
Appendix B. Document Change Log
 [RFC Editor: Please delete this section on publication as RFC.]
B.1. Changes to draft-ietf-lisp-rfc8378bis-05
 * Posted December 2025 (Dino).
 * Update document timer and references.
 * Add Prasad as co-author as he will be editor as we move forward
 with this document.
B.2. Changes to draft-ietf-lisp-rfc8378bis-04
 * Posted August 2025 (Dino).
 * Update document timer and references.
B.3. Changes to draft-ietf-lisp-rfc8378bis-03
 * Posted February 2025 (Mike McBride).
 * Modified the definition of RLE
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 * Added a definition for Overlay Distribution Tree
B.4. Changes to draft-ietf-lisp-rfc8378bis-00/01/02
 * Posted February 2025 (Mike McBride).
 * Dropped "architecture and protocols" from Abstract.
 * Replaced "situations" with "deployments".
 * Added definition for Replication List Entry (RLE).
 * Dropped "architecture and protocols" from Abstract.
 * Removed unnecessary sentences.
 * Reorg'd Table of Contents to include Terminology, Definitions, and
 Requirements Language.
 * Cleaned up Figure 1.
 * Replaced "receiver site" with "Receiver-site 2"
 * Added a reference to RFC 8111.
 * Changed a few MAYs to may.
 * Corrected Map-Register and Map-Reply RFC from 9300 to 9301.
 * Replaced PIM DR with PIM Designated Router (DR).
 * Changed a couple of "required" to "REQUIRED".
 * Replaced "p-bit" with "P-bit".
 * Replaced "suggested" with "RECOMMENDED".
 * Added a new first sentence to the security section and dropped
 another sentence.
 * Replaced references to LISP-SEC with RFC9303 normative reference.
B.5. Changes to draft-ietf-lisp-rfc8378bis-00
 * Posted August 2024.
 * Make draft-farinacci-lisp-rfc8378bis-00 working group document
 draft-ietf-lisp-rfc8378bis-00.
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B.6. Changes to draft-farinacci-lisp-rfc8378bis-00
 * Posted May 2024.
 * Starting with [RFC8378] to move it to a bis document for standards
 track.
 * Changed references to standards track RFCs.
Authors' Addresses
 Victor Moreno
 Google LLC
 1600 Amphitheatre Pkwy
 Mountain View, CA 94043
 United States of America
 Email: vimoreno@google.com
 Dino Farinacci
 lispers.net
 San Jose, CA 95120
 United States of America
 Email: farinacci@gmail.com
 Vengada Prasad Govindan
 Cisco
 San Jose, CA
 United States of America
 Email: venggovi@cisco.com
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