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Multicast Lessons Learned from Decades of Deployment Experience
draft-mcbride-mboned-lessons-learned-01

Document Type Active Internet-Draft (individual)
Authors Dino Farinacci , Lenny Giuliano , Mike McBride
Last updated 2022-10-24
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draft-mcbride-mboned-lessons-learned-01
Network Working Group                                       D. Farinacci
Internet-Draft                                               lispers.net
Intended status: Informational                               L. Giuliano
Expires: 27 April 2023                                           Juniper
                                                              M. McBride
                                                               Futurewei
                                                         24 October 2022

    Multicast Lessons Learned from Decades of Deployment Experience
                draft-mcbride-mboned-lessons-learned-01

Abstract

   This document gives a historical perspective about the design and
   deployment of multicast routing protocols.  The document describes
   the technical challenges discovered from building these protocols.
   Even though multicast has enjoyed success of deployment in special
   use-cases, we discuss what were, and are, the obstacles for mass
   deployment across the Internet.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 27 April 2023.

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   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
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   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components

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   extracted from this document must include Revised BSD License text as
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Glossary  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Lessons learned about IP Multicast over the last 30 years . .   4
     3.1.  DVMRP . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Shared vs Source Trees  . . . . . . . . . . . . . . . . .   4
     3.3.  Data Driven State Creation and RPF  . . . . . . . . . . .   6
     3.4.  MPLS MVPNs  . . . . . . . . . . . . . . . . . . . . . . .   6
     3.5.  SD and SDR  . . . . . . . . . . . . . . . . . . . . . . .   7
     3.6.  All or Nothing Problem  . . . . . . . . . . . . . . . . .   8
     3.7.  Network Based Source Discovery  . . . . . . . . . . . . .   9
     3.8.  Premature Optimization  . . . . . . . . . . . . . . . . .   9
     3.9.  Kernel vs User Space  . . . . . . . . . . . . . . . . . .  10
     3.10. IGMP  . . . . . . . . . . . . . . . . . . . . . . . . . .  10
     3.11. 802.11  . . . . . . . . . . . . . . . . . . . . . . . . .  10
   4.  Conclusions . . . . . . . . . . . . . . . . . . . . . . . . .  11
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   7.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .  11
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   There are many multicast related drafts and RFC's around IPv4, IPv6,
   tunnel and label based solutions.  These protocols include DVMRP
   [RFC1075], PIM-DM [RFC3973], PIM-SM [RFC7761], PIM-BIDIR [RFC5015],
   PIM-SSM [RFC4607], MSDP [RFC3618], MBGP [RFC2858], MVPN [RFC6513],
   P2MP RSVP-TE [RFC4875], MLDP [RFC6388], BIER [RFC8279], LISP
   [RFC6830], MOSPF [RFC1584] IGMP [RFC2236], MLD [RFC3810] and several
   others.  Perhaps due to these many multicast protocols, and their
   perceived complexity over unicast, there has been much angst over
   deploying IP Multicast over the last 30 years.  It is not uncommon,
   with technical topics on multicast routing, for the discussion to
   evolve into what makes up a multicast address, whether that address
   identifies the source content or the set of receivers, does multicast
   create too much state on the network, why hasn't it captured the
   heart of the internet, why is it so complicated, what's the best
   multicast protocol to use, amongst many other questions.  Despite the
   existence of multicast related BCPs, the authors felt it important to
   have a draft which helps answer some of these questions through
   identifying the lessons learned from multicast development and

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   deployment over the last 30 years.  We attempt to better understand
   the current, and future, state of multicast affairs by reviewing the
   distractions, hype and innovation over the years and what we've
   learned from the evolution of IP Multicast.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Glossary

   PIM: Protocol Independent Multicast

   PIM-DM: PIM Dense Mode

   PIM-SM: PIM Sparse Mode

   PIM-BIDIR: PIM Bi-Directional

   PIM-SSM: PIM Source Specific Multicast

   DVMRP: Distance Vector Multicast Routing Protocol

   MVPN: Multicast Virtual Private Network

   MSDP: Multicast Source Discovery Protocol

   MBGP: Multi-protocol Border Gateway Protocol

   BIER: Bit Indexed Explicit Routing

   IGMP: Internet Group Management Protocol

   MLD: Multicast Listener Discovery

   P2MP RSVP-TE: Point-to-Multipoint TE Label Switched Paths

   MLDP: Multicast Label Distribution Protocol

   MOSPF: Multicast OSPF

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3.  Lessons learned about IP Multicast over the last 30 years

   We will address various topics, in this section, which are relevant
   enough to warrant a discussion around what we've learned since their
   development.  We will start with one of the original multicast
   routing protocols called Distance Vector Multicast Routing Protocol
   (DVMRP).

3.1.  DVMRP

   DVMRP computes its own routing table to determine the best path back
   to the source.  DVMRP uses a distance-vector routing algorithm.  This
   algorithm requires that each router periodically inform its neighbors
   of its routing table.  DVMRP was a unicast routing algorithm but it
   had tree building messages which formed distribution trees which
   could be pruned.  There are no join messages in DVMRP because the
   RPF-tree is the default distribution tree.  The flooding and pruning
   of DVMRP was a good initial solution but we quickly realized that it
   wouldn't scale when using increasingly higher bit rates for multicast
   content.  Using the network to discover sources was also something
   originally thought to be a good idea but later discovered to be
   resource and state intensive.  DVMRP is a flood and prune distance
   vector protocol, similar to RIP, that relied on a hop count and
   depended upon itself as a routing protocol to build the RPF table
   rather than using existing unicast routing tables to build the rpf
   table as, the later developed, PIM-SM does.  DVMRP worked good for
   small scale deployments but began to suffer when deployed in larger
   multicast environments so we needed better solutions.

3.2.  Shared vs Source Trees

   With PIM shared trees, all sources send to a root of a shared
   distribution tree called the Rendezvous Point (RP).  When multicast
   group members join a group, they cause branches of the distribution
   tree to be appended to the existing shared tree.  New sources that
   send to the multicast group, send their traffic to the RP so existing
   receivers can receive packets.  The path multicast packets take, are
   from the source encapsulated to the RP and then natively sent on the
   shared-tree branches.  When a better/shorter path is desired, the
   source tree can be built.  A source-tree is a multicast distribution
   tree routed at the source.  As receivers on the shared-tree discover
   new sources, they join those sources on the source tree.  The path on
   the source tree is determined by the unicast routing table and is
   also known as the "RPF path".  With source trees, on the other hand,
   multicast traffic bypasses the RP and instead flows from the
   multicast source down the tree towards the receivers using the
   multicast forwarding table and the shortest available path.  There is
   machinery to allow the multicast data to switch from the shared tree

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   to a source tree once the source is discovered.  Shared trees were
   designed to reduce state at a time when memory was scarce and
   expensive, while shortest path trees were simpler, and more optimal,
   but consumed more state.

   Utilizing the network to provide the discovery of sources and
   receivers, and the machinery necessary to provide it, was an
   important development at the time.  But there was no way to discover
   sources when adhering to this Deering model, The Deering model was
   like an ethernet and sources could just send and receivers would just
   receive the packets.  When Deering augmented multicast routing, the
   receivers then needed to be discovered, so he added IGMP.  But then
   he decided to not have source discovery and as he continued
   developing the model, he added DVMRP where the sources still didn't
   need to be discovered because their packets would flow down a default
   distribution tree and then later pruned the per-group tree so packets
   wouldn't flow where there were no receivers.  When PIM was built, we
   wanted to change the default behavior to where the multicast packets
   would go nowhere and hence explicit joins built a tree.  We had to
   fix the flood-and-prune problem that DVMRP had.  We fixed that
   problem but didn't provide any explicit signaling from the source to
   discover them.  So the multicast routing protocol discovered the
   sources (via the PIM shared-tree).

   Having two types of trees was the hard part.  Switching from one tree
   (shared) to the other (source) was a difficult routing distribution
   problem.  Because as you joined the source-tree, you had to prune
   that source from the shared-tree so duplicates wouldn't continue for
   a long time.  As protocol designers and implementors, that was a
   challenge to get right.  What we then later realized was that we
   needed source trees which discover the multicast source outside of
   the network thus removing the source discovery burden from the
   network.  Source-discovery originally had to be performed in the
   network because the multicast service model did not have a signaling
   mechanism like we now have with SSM and IGMPv3.

   During this process we also learned that PIM-SM (or more generally
   ASM (Any Source Multicast)) is more susceptible to DoS attacks by
   unwanted sources than is PIM-SSM.  And address allocation with ASM is
   much more restrictive than it is with PIM-SSM.

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3.3.  Data Driven State Creation and RPF

   When a router, with a directly connected source (First Hop Router),
   receives the first multicast packet of a stream, it selects an
   optimal route from the unicast routing table based on the source
   address of the packet.  The outbound interface of the unicast route,
   towards the source, is the RPF interface, and the next hop of the
   route is the RPF neighbor.  The router compares the inbound interface
   of the packet with the RPF interface of the selected RPF route.  If
   the inbound interface is the same as the RPF interface, the router
   considers that the packet has arrived on the correct path from the
   source and forwards the packet downstream.  If a router does a lookup
   in the unicast routing table to perform an RPF check on every
   multicast data packet received, system resources would be
   overwhelmed.  To save system resources, a router first performs a
   lookup for the matching (S, G) entry after receiving a data packet
   sent from a source to a group.  If no matching (S, G) entry is found,
   the router performs an RPF check to find the RPF interface for the
   packet.  The router then creates a multicast route with the RPF
   interface as the upstream interface towards the source and delivers
   the route to the multicast forwarding information base (MFIB).  If
   the RPF check succeeds, the inbound interface of the packet is the
   RPF interface, and the router forwards the packet to all the
   downstream interfaces in the forwarding entry.  If the RPF check
   fails, the packet has been forwarded along an incorrect path, so the
   router drops the packet.  The RPF is a security feature but it has
   caused some problems.  When there are RPF changes, inconsistencies in
   the MFIB are created which can cause forwarding failures.  Problems
   may occur when hosts (not ip forwarders) are also configured with RPF
   check.  It is important to note that SSM doesn't have the data-driven
   state creation described above.  It's also important to note the
   subtle difference between a "state problem" and a "state problem on a
   particular platform from a particular vendor".

   PIM runs on a control-plane processor where the multicast routing
   table is maintained, and (S,G) state is downloaded to data-plane
   hardware forwarders.  Whenever there is an RPF change, all routes
   that had changed in the multicast routing table have to get updated
   to the hardware forwarders.

3.4.  MPLS MVPNs

   Multicast was not originally supported with MPLS.  That is a lesson
   learned in and of itself.  The workaround was point-to-point GRE
   tunnels from CE to CE which was not scalable when having many CE
   routers.  MVPN solutions were complicated at times in the ietf.  The
   MVPN complexity was organic because PE based unicast VPNs were
   already deployed.  So it didn't allow for simpler multicast designs.

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   The architecture was already built, multicast functionality was an
   incremental add-on, which made it easier to deploy but the cost of
   running the service was the same, or worse, than running unicast
   VPNs.  We had years of debate about PIM based draft-rosen mvpn vs bgp
   based mvpn using P2MP RSVP-TE.  Cisco wound up progressing an
   independent submission with [RFC6037] because it defined procedures
   which predated the publication of IETF mvpn standards, and these
   procedures differ in some respects from a fully standards-compliant
   implementation.  Eventually the pim and bgp based mvpn solutions were
   progressed together in Multicast in MPLS/BGP IP VPNs in [RFC6513].
   Perhaps one lesson learned here is that there will often be a
   conflict between providing timely implementations for customer needs
   vs waiting for the untimeliness of standards to work themselves out.
   A combined draft from the beginning, providing multiple multicast vpn
   solutions, would have been helpful in preventing years of conflict
   and non standard compliant solutions.  Another lesson is that it was
   good to decouple the control plane from the data plane so that the
   control plane could scale better and the dataplane could have more
   options.  Tunnels may now be built by PIM (any flavor), Multicast LDP
   (p2mp or mp2mp), RSVP-TE p2mp and we can map multiple provider
   multicast service interface's (PMSI) onto one aggregated tunnel.

3.5.  SD and SDR

   SD and SDR were good initial applications but we didn't go far enough
   with them to help source discovery since the app layer is indeed a
   better place to handle source discovery (than the network).  SDR is a
   session directory tool designed to allow the advertisement and
   joining of multicast streams particularly targeted for the Mbone.
   The Mbone (multicast backbone) was an experimental backbone and
   virtual network built on top of the Internet for carrying IP
   multicast traffic.  The Session Directory Revised tool (SDR) was
   developed to help discover the group and port used for a multicast
   multimedia session.  The original Session Directory (SD) tool was
   written by Lawrence Berkley Labs and was replaced by SDR.  SDR is a
   multicast application that listens for SAP packets on a well known
   multicast group.  These SAP packets contain a session description,
   the time the session is active, its IP multicast group addresses,
   media format, contact person and other information about the
   advertised multimedia session.  In hindsight we should have continued
   developing SDR to more fully help with source discovery perhaps by
   utilizing http.  That would have been better than focusing on the
   network to provide multicast source discovery.

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3.6.  All or Nothing Problem

   For multicast to function, every layer 3 hop between the sourcing and
   receiving end hosts must support a multicast routing protocol.  This
   may not be a difficult challenge for enterprises and walled-garden
   networks where the benefits of multicast are perceived to be much
   greater than the costs to deploy (eg, financial, video distribution,
   MVPN SPs, etc).  However, on the global Internet, where the cost/
   benefits of multicast (or any service, for that matter) are not
   likely to ever be universally agreed upon, this "all or nothing"
   requirement tends to create an insurmountable barrier.  It should be
   noted that IPv6 suffers the same challenge, which explains why IPv6
   has not been ubiquitously deployed across the Internet to the same
   degree as IPv4, despite decades of trying.  Simply put, any
   technology that requires new protocols to be enabled on every
   interface on every router and firewall on the Internet is not likely
   to succeed.  One approach to address this challenge is to develop
   solutions that facilitate incremental deployment and minimize/
   eliminate the need for coordination of multiple parties.  Overlay
   networking is one such approach and allows the service to work for
   end users without requiring every underlay hop to support multicast-
   only the layer 3 hops in the overlay topology require multicast
   support.  For example, AMT [RFC7450] allows end users on unicast-only
   networks to receive multicast content by dynamically tunneling to
   devices (AMT Relays) on multicast-enabled networks.  This empowers
   interested end users to enjoy the service while also enabling content
   providers and operators who have deployed multicast to realize the
   benefits of more efficient delivery while tunneling over the parts of
   the network (last/middle/first mile) that haven't deployed multicast.
   Further, this incremental approach can provide the necessary
   incentive for operators who haven't deployed multicast natively to do
   so in order to avoid carrying duplicate tunneled traffic.  Another
   example is Locator/ID Separation Protocol (LISP) [RFC8378], where
   multicast sources and receivers can be on the overlay and work with a
   any combination of unicast and/or native multicast delivery from the
   underlay.  Endpoint identifiers (EIDs) are assigned to end hosts.
   Routing locators (RLOCs) are assigned to devices (primarily routers)
   that make up the global routing system.The LISP overlay nodes can
   roam while keeping their same EID address, can be multi-homed to
   load-split packets across multiple interfaces, and can encrypt
   packets at the overlay layer (freeing applications from dealing with
   security).

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3.7.  Network Based Source Discovery

   In ASM, the network is responsible for discovering all multicast
   sources.  This responsibility leads to massive protocol complexity,
   which imposes a huge operational cost for designing, operating and
   troubleshooting multicast.  In SSM, source discovery is moved out of
   network and is handled by some sort of out-of-band mechanism,
   typically in the application layer.  By eliminating network-based
   source discovery in SSM, we eliminate the need for shared trees, PIM
   register message encap/decap, RPs, SPT-switchover, data-driven state
   creation and MSDP, and the resulting protocol, PIM-SSM, is
   dramatically simpler than previous ASM routing protocols.  Indeed,
   PIM-SSM is merely a small subset of PIM-SM functionality.  The key
   insight is that source discovery is not a function the network should
   provide.  One would never expect ISIS/OSPF and BGP to discover and
   maintain a globally synchronized database of all active websites on
   the Internet, yet that is precisely what is required of PIM-SM and
   MSDP for ASM.  This insight can apply more generally to other
   functions, like accounting, access control, transport reliability,
   etc.  One simple heuristic for whether a function should exist in the
   multicast routing protocol is to simply ask what would unicast do
   (WWUD)?  If unicast routing protocols like OSPF, ISIS or BGP do not
   provide such a function, then multicast routing protocols like PIM
   should not be expected to provide that function either.  Further,
   moving functionality to the application layer, rather than in the
   network layer, allows allows faster innovation and greater levels of
   creativity, as these two layers tend to have vastly different
   requirements, expectations (and, therefore upgrade cycles) for
   stability, scale, functionality and innovation.

3.8.  Premature Optimization

   Premature optimization can saddle the protocols with complexity
   burdens long after the optimizations are no longer relevant or even
   before the optimizations can be used.  Typically those optimizations
   are implemented for scale even though you don't need or see a need
   for them in early deployments.  But they must be thought ahead of
   time and planned for (that means designed and implemented up front).
   Shared trees were born in the 1990s out of a (well-founded at the
   time) concern for state exhaustion when memory was a scarce resource.
   As memory got cheaper and more abundant, these concerns were reduced,
   but the complexity remained.  It was once ironically noted that we
   eliminated the state problem by making the protocols so complex that
   no one deployed them.  Although, to be fair, other protocols also
   have had state problems and private enterprises have successfully
   used multicast in their wall-gardens without state problems.

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3.9.  Kernel vs User Space

   In hindsight, what we should have done with multicast is the same
   thing QUIC did which is implemented as a library rather than in the
   kernel.  If we had done that, then when the app is deployed that
   needs a network function, it comes at the same time (inside the app).
   This is similar to what we have done with AMT in VLC which was a
   practical decision to get apps access to a native multicast cloud.

   By packaging the protocol stack in the application, it allows a
   developer to add features and fix bugs quickly.  And get the updates
   deployed quickly by having users download and update the app.  This
   rather modern way of distributing new code has proved successful in
   may mobile and cloud based environments.  With respect to multicast,
   we could have made faster deployed changes to IGMP as well as any
   tunneling technology we felt useful.

3.10.  IGMP

   IGMPv1 was the first protocol to allow end hosts to indicate their
   interest in receiving a multicast stream.  There was no message to
   indicate the receiver has left receiving the multicast stream so the
   router had to eventually figure it out.  This caused bandwidth
   problems especially when quickly changing channels.  IGMPv2 provided
   a leave message to prevent wasted bandwidth.  And IGMPv3 provided
   support for source specific multicast.  IGMPv1 and IGMPv2 do not have
   the capability to specify a particular sender of multicast traffic.
   This capability is provided in IGMPv3.

   In hindsight we could have easily developed SSM with IGMPv2 from the
   start.  All an (S,G) is, is a longer group address.  So if we changed
   IGMPv2 to have a more general encoding, we would have created IPv6
   groups, IPv6 (S,G), and IPv4 (S,G) encoding all at the same time.
   And, if we had made it a library, it would have likely been deployed
   faster.  Additionally, because we were working on "Integrated IS-IS"
   and "IPv6" all at the same time, we could have developed one protocol
   - similar to how we do it for BGP today.  PIM was integrated but it
   was developed as "ships in the night" with other protocols.

3.11.  802.11

   We've learned many things over the years about the problems (such as
   high packet error rates, no acknowledgements and low data rates) with
   deploying multicast in 802.11 (Wi-Fi) networks.  We even created
   [RFC9119] specifically to address all the many ways multicast is
   problematic over Wi-Fi.  Performance issues, for instance, have been
   observed over the years, when multicast packets transmit over IEEE
   802 wireless media, so much so that that it is often disallowed over

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   Wi-Fi networks.  Various workarounds have been developed including
   converting multicast to unicast at layer 2 (aka, ingress replication)
   in order to more successfully transit the wireless medium.  There are
   various optimizations that can be implemented to mitigate some of the
   many issues involving multicast over Wi-Fi.  The lesson we've learned
   now is that we (vendors, IETF) should have worked closely with the
   IEEE many years ago on detailing the problems in order to improve the
   performance of multicast transmissions at Layer 2.  The IEEE is now
   designing features to improve multicast performance over Wi-Fi but
   it's expensive to do so and will take time.

4.  Conclusions

5.  IANA Considerations

   N/A

6.  Security Considerations

7.  Acknowledgement

   Beau Williamson's publications helped with some of the history of the
   protocols discussed.

8.  Normative References

   [RFC1075]  Waitzman, D., Partridge, C., and S. Deering, "Distance
              Vector Multicast Routing Protocol", RFC 1075,
              DOI 10.17487/RFC1075, November 1988,
              <https://www.rfc-editor.org/info/rfc1075>.

   [RFC1584]  Moy, J., "Multicast Extensions to OSPF", RFC 1584,
              DOI 10.17487/RFC1584, March 1994,
              <https://www.rfc-editor.org/info/rfc1584>.

   [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>.

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   [RFC2858]  Bates, T., Rekhter, Y., Chandra, R., and D. Katz,
              "Multiprotocol Extensions for BGP-4", RFC 2858,
              DOI 10.17487/RFC2858, June 2000,
              <https://www.rfc-editor.org/info/rfc2858>.

   [RFC3618]  Fenner, B., Ed. and D. Meyer, Ed., "Multicast Source
              Discovery Protocol (MSDP)", RFC 3618,
              DOI 10.17487/RFC3618, October 2003,
              <https://www.rfc-editor.org/info/rfc3618>.

   [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>.

   [RFC3973]  Adams, A., Nicholas, J., and W. Siadak, "Protocol
              Independent Multicast - Dense Mode (PIM-DM): Protocol
              Specification (Revised)", RFC 3973, DOI 10.17487/RFC3973,
              January 2005, <https://www.rfc-editor.org/info/rfc3973>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <https://www.rfc-editor.org/info/rfc4271>.

   [RFC4607]  Holbrook, H. and B. Cain, "Source-Specific Multicast for
              IP", RFC 4607, DOI 10.17487/RFC4607, August 2006,
              <https://www.rfc-editor.org/info/rfc4607>.

   [RFC4875]  Aggarwal, R., Ed., Papadimitriou, D., Ed., and S.
              Yasukawa, Ed., "Extensions to Resource Reservation
              Protocol - Traffic Engineering (RSVP-TE) for Point-to-
              Multipoint TE Label Switched Paths (LSPs)", RFC 4875,
              DOI 10.17487/RFC4875, May 2007,
              <https://www.rfc-editor.org/info/rfc4875>.

   [RFC5015]  Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
              "Bidirectional Protocol Independent Multicast (BIDIR-
              PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007,
              <https://www.rfc-editor.org/info/rfc5015>.

   [RFC6037]  Rosen, E., Ed., Cai, Y., Ed., and IJ. Wijnands, "Cisco
              Systems' Solution for Multicast in BGP/MPLS IP VPNs",
              RFC 6037, DOI 10.17487/RFC6037, October 2010,
              <https://www.rfc-editor.org/info/rfc6037>.

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   [RFC6388]  Wijnands, IJ., Ed., Minei, I., Ed., Kompella, K., and B.
              Thomas, "Label Distribution Protocol Extensions for Point-
              to-Multipoint and Multipoint-to-Multipoint Label Switched
              Paths", RFC 6388, DOI 10.17487/RFC6388, November 2011,
              <https://www.rfc-editor.org/info/rfc6388>.

   [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>.

   [RFC6830]  Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
              Locator/ID Separation Protocol (LISP)", RFC 6830,
              DOI 10.17487/RFC6830, January 2013,
              <https://www.rfc-editor.org/info/rfc6830>.

   [RFC7450]  Bumgardner, G., "Automatic Multicast Tunneling", RFC 7450,
              DOI 10.17487/RFC7450, February 2015,
              <https://www.rfc-editor.org/info/rfc7450>.

   [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>.

   [RFC8279]  Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
              Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
              Explicit Replication (BIER)", RFC 8279,
              DOI 10.17487/RFC8279, November 2017,
              <https://www.rfc-editor.org/info/rfc8279>.

   [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>.

   [RFC9119]  Perkins, C., McBride, M., Stanley, D., Kumari, W., and JC.
              Zúñiga, "Multicast Considerations over IEEE 802 Wireless
              Media", RFC 9119, DOI 10.17487/RFC9119, October 2021,
              <https://www.rfc-editor.org/info/rfc9119>.

Authors' Addresses

   Dino Farinacci
   lispers.net
   Email: farinacci@gmail.com

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   Lenny Giuliano
   Juniper
   Email: lenny@juniper.net

   Mike McBride
   Futurewei
   Email: michael.mcbride@futurewei.com

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