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Versions: (draft-acg-mboned-multicast-models) 00 01 02

Mboned                                                    M. Abrahamsson
Internet-Draft                                                 T-Systems
Intended status: Best Current Practice                          T. Chown
Expires: January 3, 2019                                            Jisc
                                                             L. Giuliano
                                                  Juniper Networks, Inc.
                                                               T. Eckert
                                                            July 2, 2018

               Deprecating ASM for Interdomain Multicast


   This document recommends deprecation of the use of Any-Source
   Multicast (ASM) for interdomain multicast.  It recommends the use of
   Source-Specific Multicast (SSM) for interdomain multicast
   applications, and that hosts and routers that are expected to handle
   such applications fully support SSM.  The recommendations in this
   document do not preclude the continued use of ASM within a single
   organisation or domain, and are especially easy to adopt when already
   using the preferred ASM protocol options there (PIM-SM).

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in "Key words for use in
   RFCs to Indicate Requirement Levels" [RFC2119].

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 January 3, 2019.

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Copyright Notice

   Copyright (c) 2018 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 Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Multicast routing protocols . . . . . . . . . . . . . . . . .   3
     2.1.  ASM routing protocols . . . . . . . . . . . . . . . . . .   4
     2.2.  SSM Routing protocols . . . . . . . . . . . . . . . . . .   5
   3.  Discussion  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Observations on ASM and SSM deployments . . . . . . . . .   5
     3.2.  Advantages of SSM for interdomain multicast . . . . . . .   6
   4.  Recommendations . . . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  Deprecating use of ASM for interdomain multicast  . . . .   7
     4.2.  Including network support for IGMPv3 / MLDv2  . . . . . .   8
     4.3.  Building application support for SSM  . . . . . . . . . .   8
     4.4.  Preferring SSM applications intradomain . . . . . . . . .   9
     4.5.  Documenting common practices for SSM support in
           applications. . . . . . . . . . . . . . . . . . . . . . .   9
     4.6.  Documenting an ASM/SSM protocol mapping mechanism . . . .  10
     4.7.  Not filtering ASM addressing between domains  . . . . . .  10
     4.8.  Not precluding Intradomain ASM  . . . . . . . . . . . . .  10
   5.  Congestion Control Considerations . . . . . . . . . . . . . .  11
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  11
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   IP Multicast has been deployed in various forms, within private
   networks, the wider Internet, and federated networks such as national
   or regional research networks.  While a number of service models have

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   been published, and in many cases revised over time, there has been
   no strong recommendation made by the IETF on the appropriateness of
   those models to certain scenarios, even though vendors and
   federations have often made such recommendations.

   This document addresses this gap by making a BCP-level recommendation
   to deprecate the use of ASM for interdomain multicast, leaving SSM as
   the remaining interdomain mode of multicast.  This recommendation
   thus also implicitly states that all hosts and routers that are
   expected to support interdomain multicast applications fully support

   This document does not make any statement on the use of ASM within a
   single domain or organisation, and therefore does not preclude its
   use.  Indeed, there are application contexts for which ASM is
   currently still widely considered well-suited within a single domain.

   The main issue in most cases with moving to SSM is application
   support.  Many applications will first get used intradomain but only
   later interdomain.  Therefore, this document recommends making
   applications support SSM, even when they are initially meant to be
   just used intradomain.  As explained below, SSM applications are
   readily compatible with existing intradomain ASM deployments that
   follow the current IETF standard protocol recommendations.

2.  Multicast routing protocols

   The general IP multicast service model [RFC1112] is that sender(s)
   send to a multicast group address, receivers express an interest in
   traffic sent to a given multicast group address, and that routers use
   multicast routing protocols to determine how to deliver traffic from
   the sender(s) to the receivers.

   Two high-level flavours of this service model have evolved over time.
   In Any-Source Multicast (ASM), any number of sources may transmit
   multicast packets, and those sources may come and go over the course
   of a multicast session without being known a priori.  In ASM,
   receivers express interest only in a given multicast group address,
   and the multicast routing protocol facilitates source discovery at
   the network layer.  ASM is simply the name given to the 1989 RFC1112
   IP Multicast model when in around 2000 the idea for the alternative
   SSM model was taking shape: In Source-Specific Multicast (SSM) the
   specific source(s) that may send traffic to the group are known in
   advance by the receivers, or may be determined during a session,
   typically through an out-of-band protocol sitting above the network
   layer.  Thus in SSM, receivers express interest in both a multicast
   group address and specific associated source address(es).

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   IANA has reserved specific ranges of IPv4 and IPv6 address space for
   multicast addressing.  Guidelines for IPv4 multicast address
   assignments can be found in [RFC5771], while guidelines for IPv6
   multicast address assignments can be found in [RFC2375] and
   [RFC3307].  The IPv6 multicast address format is described in

2.1.  ASM routing protocols

   The most commonly deployed ASM routing protocol is Protocol
   Independent Multicast - Sparse Mode, or PIM-SM, as detailed in
   [RFC7761].  PIM-SM, as the name suggests, was designed to be used in
   scenarios where the subnets with receivers are sparsely distributed
   throughout the network.  Because it does not know sender addresses in
   advance, PIM-SM uses the concept of a Rendezvous Point (RP) to 'marry
   up' senders and receivers, and all routers in a PIM-SM domain are
   configured to use specific RP(s), either explicitly or through
   dynamic RP discovery protocols.

   To enable PIM-SM to work between multiple domains, i.e., to allow an
   RP in one domain to learn the existence of a source in another
   domain, an inter-RP signalling protocol known as Multicast Source
   Discovery Protocol (MSDP) [RFC3618] is used.  Deployment scenarios
   for MSDP are given in [RFC4611].  MSDP has remained an Experimental
   protocol since its publication in 2003.  One core reason for this is
   the need to flood information about all active sources for all active
   applications to the RPs in all the domains in an MSDP peering mesh -
   even if there is no receiver for a given application in a domain.
   This is the key scalability and security issue with MSDP and also the
   reason why it was not extended to support IPv6.

   To this day, there is no IETF Proposed Standard level interdomain
   solution for IPv4 ASM multicast because MSDP was the "best" component
   for the interdomain discovery problem, and it stayed Experimental.
   Other protocol options where investigated at the same time but did
   achieve at most achieve IETF informational status and are now
   historic (e.g: [RFC3913]).

   Due to the availability of more bits in an IPv6 address than in IPv4,
   an IPv6-specific mechanism was able to be designed in support of
   interdomain ASM with PIM-SM.  Embedded-RP [RFC3956] allows routers
   supporting the protocol to determine the RP for the group without any
   prior configuration or discovery protocols, simply by observing the
   unicast RP address that is embedded (included) in the IPv6 multicast
   group address.  Embedded-RP allows PIM-SM operation across any IPv6
   network (intradomain but especially interdomain) in which there is an
   end-to-end path of routers supporting the mechanism.

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2.2.  SSM Routing protocols

   SSM is detailed in [RFC4607].  It is in effect a subset of PIM-SM
   where no RP is used.  Note that there is no separate document for
   PIM-SSM, it just leverages a subset of [RFC7761].

   PIM-SSM expects that sender source address(es) are known in advance
   by receivers; i.e., a given source's IP address is known (by some out
   of band mechanism), and thus the receiver's router can send a PIM
   JOIN directly towards the sender, without needing to use an RP.

   IPv4 addresses in the 232/8 ( to range are
   designated as source-specific multicast (SSM) destination addresses
   and are reserved for use by source-specific applications and
   protocols.  See [RFC4607].  For IPv6, the address prefix FF3x::/32 is
   reserved for source-specific multicast use.

3.  Discussion

3.1.  Observations on ASM and SSM deployments

   In enterprise and campus scenarios, ASM in the form of PIM-SM is
   likely the most commonly deployed multicast protocol and has
   generally replaced PIM-DM [RFC3973], which is an IETF Experimental
   category RFC, while PIM-SM is full Internet Standard.  The
   configuration and management of an RP (even with RP redundancy)
   within a single domain is well understood operational practice.
   However, if interworking with external PIM domains is needed in IPv4
   multicast deployments, interdomain MSDP is required to exchange
   information about sources between domain RPs.  The problems with this
   use of MSDP are as explained above.  They are the problems that make
   MSDP an Experimental protocol, and that make it (in these
   deployments) a complex and fragile protocol to administer and
   troubleshoot (flooding RPF rules, state attack protection, undesired
   source filtering, ...).

   PIM-SM is a general purpose protocol that can handle all use cases.
   In particular, it was designed for cases such as videoconferencing
   where multiple sources may come and go during a multicast session.
   But for cases where a single, persistent source for a group is used,
   and receivers can be configured to know of that source, PIM-SM has
   unnecessary complexity.  In these applications it is typically only
   necessary to extend the configuration or signaling for the IP
   multicast group to be used with the additional information on the IP
   multicast source to be used.  There are also various techniques to
   use a single logical "anycast" source address supported by two or
   more redundant senders to give additional reliability for SSM, and to

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   offer simpler deployment by using that address as a "static"/"well-
   known" address.

   As explained above, MSDP was not taken forward to IPv6.  Instead, the
   proposed interdomain ASM solution for PIM-SM with IPv6 is Embedded-
   RP, which allows the RP address for a multicast group to be embedded
   in the group address, making RP discovery automatic, if all routers
   on the path between a receiver and a sender support the protocol.
   Embedded-RP can support lightweight ad-hoc deployments.  However, it
   relies on a single RP for an entire group that could only be made
   resilient within one domain.  While this approach solves the MSDP
   issues, it does not solve the problem of unauthorised sources sending
   traffic to ASM multicast groups; this security issues is one of
   biggest problem of interdomain multicast.  Embedded-RP was run
   successfully between European and US academic networks during the
   6NET project in 2004/05.  Its usage generally remains constrained to
   academic networks.

   As stated in RFC 4607, SSM is particularly well-suited to
   dissemination-style applications with one or more senders whose
   identities are known (by some mechanism) before the application
   starts running - or applications that have some existing signaling
   indicating multicast groups, where the additional source address can
   easily be added - for example electronic programming guide signalling
   in IPTV applications.  PIM-SSM is therefore very well-suited to
   applications such as classic linear broadcast TV over IP.

   SSM requires applications, host operating systems and their subnet
   routers using it to support the new(er) IGMPv3 [RFC3376] and MLDv2
   [RFC3810] protocols.  While delayed delivery of support in some OSes
   has meant that adoption of SSM has been slower than might have been
   expected, or hoped, and was a historical reason to use ASM rather
   than SSM, support for IGMPv3 and MLDv2 has become widespread in
   common OSes for several years (Windows, MacOS, Linux/Android).

3.2.  Advantages of SSM for interdomain multicast

   A significant benefit of SSM is its reduced complexity through
   eliminating the network-based source discovery required in ASM.  This
   means there are no RPs, shared trees, Shortest Path Tree (SPT)
   switchovers, PIM registers, MSDP, or data-driven state creation
   elements to support, or any requirement to run dynamic RP discovery
   and redundancy signaling protocols such as BSR.  SSM is really just a
   small subset of PIM-SM, alongside the integration with IGMPv3 / MLDv2
   where the source address signaled from the receiver is immediately
   used to create (S,G) state.  Eliminating network-based source
   discovery for interdomain multicast means the vast majority of the
   complexity issues go away.

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   This reduced complexity makes SSM radically simpler to manage,
   troubleshoot and operate, particularly for network backbone
   operators, and this is the main operator motivation for the
   recommendation to deprecate the use of ASM in interdomain scenarios.
   Note that SSM operation is all standardised in PIM-SM (RFC7761).
   There is no separate specification for PIM-SSM.

   RFC 4607 details many benefits of SSM, including:

      "Elimination of cross-delivery of traffic when two sources
      simultaneously use the same source-specific destination address;

      Avoidance of the need for inter-host coordination when choosing
      source-specific addresses, as a consequence of the above;

      Avoidance of many of the router protocols and algorithms that are
      needed to provide the ASM service model."

   Further discussion can also be found in [RFC3569].

   SSM is considered more secure in that it supports access control,
   i.e. you only get packets from the sources you explicitly ask for, as
   opposed to ASM where anyone can decide to send traffic to a PIM-SM
   group address.  This topic is expanded upon in [RFC4609].

4.  Recommendations

4.1.  Deprecating use of ASM for interdomain multicast

   This document recommends that the use of ASM is deprecated for
   interdomain multicast, and thus implicitly that hosts and routers
   that are expected to support such interdomain applications fully
   support SSM and its associated protocols.  Best current practices for
   deploying interdomain multicast using SSM are documented in

   The recommendation applies to the use of ASM between domains where
   either MSDP (IPv4) or Embedded-RP (IPv6) is used for sharing
   knowledge of remote sources (MSDP) or RPs (Embedded-RP).

   This document also recommends against the interdomain use of PIM-SM
   with a (potentially redundant) RP, where multicast tunnels are used
   between domains.

   An interdomain use of ASM multicast in the context of this document
   is primarily one where PIM-SM for ASM, e.g., with RPs/MSDP/Embedded-
   RP, is run on routers operated by two or more separate operational
   entities (domains, organisations).

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   The more inclusive interpretation of this recommendation is that it
   also extends to the case where PIM may only be operated in a single
   operator domain, but where user hosts or non-PIM network edge devices
   are under different operator control.  A typical example of this case
   is an SP providing IPTV (single operator domain for PIM) to
   subscribers operating an IGMP proxy home gateway and IGMPv3/MLDv2
   hosts (computer, tablets, set-top boxes).

   While MSDP is an Experimental category IETF standard, this document
   does not propose making MSDP Historic, given its use may be desirable
   for intradomain multicast use cases (e.g., RP redundancy
   intradomain).  This may change in future documents should a successor
   to MSDP for intradomain RP redundancy ([RFC4610]) be defined to add
   better support for some currently missing operational requirements.

4.2.  Including network support for IGMPv3 / MLDv2

   This document recommends that all host and router platforms
   supporting multicast, and any security appliances that may handle
   multicast traffic, support IGMPv3 [RFC3376] and MLDv2 [RFC3810]
   (based on the version IP they intend to support).  The updated IPv6
   Node Requirements RFC [I-D.ietf-6man-rfc6434-bis] states that MLDv2
   support is a MUST in all implementations.  Such support is already
   widespread in common host and router platforms.

   Further guidance on IGMPv3 and MLDv2 is given in [RFC4604].

   It is sometimes desirable to limit the propagation of multicast
   messages in a layer 2 network, typically through a layer 2 switch
   device.  In such cases multicast snooping can be used, by which the
   switch device observes the IGMP/MLD traffic passing through it, and
   then attempts to make intelligent decisions about on which physical
   ports it should forward multicast.  Typically, ports that have not
   expressed an interest in receiving multicast for a given group would
   not have traffic for that group forwarded through them.  Such
   snooping capability should therefore support IGMPv3 and MLDv2.  There
   is further discussion in [RFC4541].

4.3.  Building application support for SSM

   There is a wide range of applications today that only support ASM
   (mostly for historic reasons), whether as software packages, or code
   embedded in devices such as set-top boxes.

   The recommendation to use SSM for interdomain multicast means that
   applications should use SSM, and operate correctly in an SSM
   environment, triggering IGMPv3/MLDv2 messages to signal use of SSM.

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   It is often thought that ASM is required for multicast applications
   where there are multiple sources.  However, RFC 4607 also describes
   how SSM can be used instead of PIM-SM for multi-party applications:

      "SSM can be used to build multi-source applications where all
      participants' identities are not known in advance, but the multi-
      source "rendezvous" functionality does not occur in the network
      layer in this case.  Just like in an application that uses unicast
      as the underlying transport, this functionality can be implemented
      by the application or by an application-layer library."

   Given all common OSes support SSM, it is then down to the programming
   language and APIs used as to whether the necessary SSM APIs are
   available.  SSM support became first ubiquitous for C/C++/Python, and
   key exceptions today include websockets used in web-browser based
   applications (see e.g.: https://github.com/nodejs/node/pull/15735/
   files introducing SSM support there in 2017).

   Some useful considerations for multicast applications can still be
   found in the relatively old [RFC3170].

4.4.  Preferring SSM applications intradomain

   If feasible, it is recommended to make applications use SSM, even if
   they are initially only meant to be used in intradomain environments
   supporting ASM.  Because PIM-SSM is a subset of PIM-SM, it should be
   possible to readily make existing intradomain PIM-SM networks
   compatible with SSM application receivers, therefore allowing
   continued use of an existing ASM PIM-SM deployment in a network with
   no or very little changes.  SSM's benefits of simplified address
   management and significantly reduced operational complexity apply
   equally to intradomain use.

   However, for some applications it may be prohibitively difficult to
   add support for signaling of source IP addresses into the

4.5.  Documenting common practices for SSM support in applications.

   Currently, there is no good document summarising best current
   practices to convert ASM applications into SSM applications, or how
   to most easily support SSM in greenfield application designs.  This
   would be useful guidance for the IETF to work on.

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4.6.  Documenting an ASM/SSM protocol mapping mechanism

   In the case of existing ASM applications that cannot readily be
   ported to SSM, it may be possible to use some form of protocol
   mapping, i.e., to have a mechanism to translate a (*,G) join or leave
   to a (S,G) join or leave, for a specific source, S.  The general
   challenge in performing such mapping is determining where the
   configured source address, S, comes from.

   There are existing vendor-specific mechanisms deployed that achieve
   this function, but none are documented in IETF documents.  This
   appears to be a useful area for the IETF to work on, but it should be
   noted that any such effort would only be an interim transition
   mechanism, and such mappings do not remove the requirement for
   applications to be allocated ASM group addresses for the

   The reason why these mechanisms should not be considered a long-term
   solution is because they introduce network operator management work,
   and need some form of address management, both of which are not
   required in SSM.

4.7.  Not filtering ASM addressing between domains

   A key benefit of SSM is that a multicast application does not need to
   be allocated a specific multicast group by the network, rather as SSM
   is inherently source-specific, it can use any group address, G, in
   the reserved range of IPv4 or IPv6 SSM addresses for its own source
   address, S.

   In principle, if interdomain ASM is deprecated, backbone operators
   could begin filtering the ranges of group addresses used by ASM.  In
   practice, this is not recommended given there will be a transition
   period from ASM to SSM, where some form of ASM-SSM mappings may be
   used, and filtering may preclude such operations.

4.8.  Not precluding Intradomain ASM

   The use of ASM within a single multicast domain, such as a campus or
   enterprise, with an RP for the site, is still relatively common
   today.  There are even global enterprise networks that have
   successfully been using PIM-SM for many years.  The operators of such
   networks most often use Anycast-RP [RFC4610] or MSDP for RP
   resilience, at the expense of the extra complexity in managing that
   configuration.  These existing practices are unaffected by this

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   This document does not preclude continued use of ASM in the
   intradomain scenario.  If an organisation, or AS, wishes to use
   multiple multicast domains within its own network border, that is a
   choice for that organisation to make, and it may then use MSDP or
   Embedded-RP internally within its own network.

5.  Congestion Control Considerations

   Traffic over non-controlled networks, which most interdomain paths
   are, must support congestion control.  This is achievable with rate
   adaptation, layered codecs, circuit breakers and/or other appropriate
   mechanisms.  See [RFC8085].

6.  Security Considerations

   This document adds no new security considerations.  It instead
   removes security issues incurred by interdomain ASM with PIM-SM/MSDP:
   infrastructure control plane attacks and application and bandwidth/
   congestion attacks from unauthorised sources sending to ASM multicast
   groups.  RFC 4609 describes the additional security benefits of using
   SSM instead of ASM.

7.  IANA Considerations

   This document makes no request of IANA.

   Note to RFC Editor: this section may be removed upon publication as
   an RFC.

8.  Acknowledgments

   The authors would like to thank members of the IETF mboned WG for
   discussions on the content of this document, with specific thanks to
   the following people for their contributions to the document: Hitoshi
   Asaeda, Dale Carder, Jake Holland, Albert Manfredi, Mike McBride, Per
   Nihlen, Greg Shepherd, James Stevens, Stig Venaas, Nils Warnke, and
   Sandy Zhang.

9.  References

9.1.  Normative References

   [RFC1112]  Deering, S., "Host extensions for IP multicasting", STD 5,
              RFC 1112, DOI 10.17487/RFC1112, August 1989,

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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC3307]  Haberman, B., "Allocation Guidelines for IPv6 Multicast
              Addresses", RFC 3307, DOI 10.17487/RFC3307, August 2002,

   [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,

   [RFC3810]  Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
              Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
              DOI 10.17487/RFC3810, June 2004,

   [RFC3956]  Savola, P. and B. Haberman, "Embedding the Rendezvous
              Point (RP) Address in an IPv6 Multicast Address",
              RFC 3956, DOI 10.17487/RFC3956, November 2004,

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <https://www.rfc-editor.org/info/rfc4291>.

   [RFC4607]  Holbrook, H. and B. Cain, "Source-Specific Multicast for
              IP", RFC 4607, DOI 10.17487/RFC4607, August 2006,

   [RFC4610]  Farinacci, D. and Y. Cai, "Anycast-RP Using Protocol
              Independent Multicast (PIM)", RFC 4610,
              DOI 10.17487/RFC4610, August 2006,

   [RFC5771]  Cotton, M., Vegoda, L., and D. Meyer, "IANA Guidelines for
              IPv4 Multicast Address Assignments", BCP 51, RFC 5771,
              DOI 10.17487/RFC5771, March 2010,

   [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>.

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9.2.  Informative References

   [RFC2375]  Hinden, R. and S. Deering, "IPv6 Multicast Address
              Assignments", RFC 2375, DOI 10.17487/RFC2375, July 1998,

   [RFC3170]  Quinn, B. and K. Almeroth, "IP Multicast Applications:
              Challenges and Solutions", RFC 3170, DOI 10.17487/RFC3170,
              September 2001, <https://www.rfc-editor.org/info/rfc3170>.

   [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>.

   [RFC3618]  Fenner, B., Ed. and D. Meyer, Ed., "Multicast Source
              Discovery Protocol (MSDP)", RFC 3618,
              DOI 10.17487/RFC3618, October 2003,

   [RFC3913]  Thaler, D., "Border Gateway Multicast Protocol (BGMP):
              Protocol Specification", RFC 3913, DOI 10.17487/RFC3913,
              September 2004, <https://www.rfc-editor.org/info/rfc3913>.

   [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>.

   [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,

   [RFC4604]  Holbrook, H., Cain, B., and B. Haberman, "Using Internet
              Group Management Protocol Version 3 (IGMPv3) and Multicast
              Listener Discovery Protocol Version 2 (MLDv2) for Source-
              Specific Multicast", RFC 4604, DOI 10.17487/RFC4604,
              August 2006, <https://www.rfc-editor.org/info/rfc4604>.

   [RFC4609]  Savola, P., Lehtonen, R., and D. Meyer, "Protocol
              Independent Multicast - Sparse Mode (PIM-SM) Multicast
              Routing Security Issues and Enhancements", RFC 4609,
              DOI 10.17487/RFC4609, October 2006,

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   [RFC4611]  McBride, M., Meylor, J., and D. Meyer, "Multicast Source
              Discovery Protocol (MSDP) Deployment Scenarios", BCP 121,
              RFC 4611, DOI 10.17487/RFC4611, August 2006,

   [RFC8085]  Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
              Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
              March 2017, <https://www.rfc-editor.org/info/rfc8085>.

   [RFC8313]  Tarapore, P., Ed., Sayko, R., Shepherd, G., Eckert, T.,
              Ed., and R. Krishnan, "Use of Multicast across Inter-
              domain Peering Points", BCP 213, RFC 8313,
              DOI 10.17487/RFC8313, January 2018,

              Chown, T., Loughney, J., and T. Winters, "IPv6 Node
              Requirements", draft-ietf-6man-rfc6434-bis-08 (work in
              progress), March 2018.

Authors' Addresses

   Mikael Abrahamsson

   Email: mikael.abrahamsson@t-systems.se

   Tim Chown
   Lumen House, Library Avenue
   Harwell Oxford, Didcot  OX11 0SG
   United Kingdom

   Email: tim.chown@jisc.ac.uk

   Lenny Giuliano
   Juniper Networks, Inc.
   2251 Corporate Park Drive
   Hemdon, Virginia  20171
   United States

   Email: lenny@juniper.net

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   Toerless Eckert
   Futurewei Technologies Inc.
   2330 Central Expy
   Santa Clara  95050

   Email: tte+ietf@cs.fau.de

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