Mboned M. Abrahamsson
Internet-Draft T-Systems
Intended status: Best Current Practice T. Chown
Expires: April 25, 2019 Jisc
L. Giuliano
Juniper Networks, Inc.
T. Eckert
Huawei
October 22, 2018
Deprecating ASM for Interdomain Multicast
draft-ietf-mboned-deprecate-interdomain-asm-01
Abstract
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 in these deployments 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 in these existing intradomain ASM
deployments.
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 "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 April 25, 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
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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 . . . . . . . . . . . . . . . . . . 4
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 . . . . . . 7
4.3. Building application support for SSM . . . . . . . . . . 8
4.4. Preferring SSM applications intradomain . . . . . . . . . 8
4.5. Documenting an ASM/SSM protocol mapping mechanism . . . . 8
4.6. Not filtering ASM addressing between domains . . . . . . 9
4.7. Not precluding Intradomain ASM . . . . . . . . . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1. Normative References . . . . . . . . . . . . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
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
been published, and in many cases revised over time, there has been
no strong recommendation made by the IETF on the appropriateness of
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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 recommended 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
SSM.
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 are initially deployed for intradomain
use and are later deployed interdomain. Therefore, this document
recommends applications support SSM, even when they are initially
intended for intradomain use. As explained below, SSM applications
are readily compatible with existing intradomain ASM deployments as
SSM is merely a subset of ASM.
2. Multicast routing protocols
Any-Source Multicast (ASM) and Source-Specific Multicast (SSM) are
the two multicast service models in use today. In ASM, as originally
described in [RFC1112], receivers express interest in joining a
multicast group address and routers use multicast routing protocols
to deliver traffic from the sender(s) to the receivers. If there are
multiple senders for a given group, traffic from all senders will be
delivered to the receiver. Since receivers specify only the group
address, the network, and therefore the multicast routing protocols,
are responsible for source discovery. In SSM, by contrast, receivers
specify both group and source when expressing interest in joining a
multicast stream. Source discovery in SSM is handled by some out-of-
band mechanism (ie, the application layer), which drastically
simplifies the network and how the multicast routing protocols
operate.
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
[RFC4291].
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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) as a
'meeting point' for sources 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, an inter-RP
signalling protocol known as Multicast Source Discovery Protocol
(MSDP) [RFC3618] is used to allow an RP in one domain to learn the
existence of a source in another domain. Deployment scenarios for
MSDP are given in [RFC4611]. MSDP floods information about all
active sources for all multicast streams to all RPs in all the
domains - even if there is no receiver for a given application in a
domain. As a result of this key scalability and security issue,
along with other deployment challenges with the protocol, MSDP was
never extended to support IPv6 and remains an Experimental protocol.
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 source discovery problem, and it is Experimental.
Other protocol options where investigated at the same time but were
never implemented or deployed 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 in which there is an end-to-end path of routers supporting
the mechanism.
2.2. SSM Routing protocols
SSM is detailed in [RFC4607]. Note that there is no separate
document for PIM-SSM as it merely leverages a subset of [RFC7761].
PIM-SSM expects that the sender's source address(es) is known in
advance by receivers by some out-of-band mechanism (typically in the
application layer), and thus the receiver's designated router can
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send a PIM JOIN directly towards the source without needing to use an
RP.
IPv4 addresses in the 232/8 (232.0.0.0 to 232.255.255.255) 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. The
configuration and management of an RP (including RP redundancy)
within a single domain is a 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. Deployment experience
has shown MSDP to be a complex and fragile protocol to manage and
troubleshoot (complex flooding RPF rules, state attack protection,
filtering of undesired sources, ...).
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. Therefore, SSM eliminates the most
components of PIM-SM.
As explained above, MSDP was not extended to support 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 for
all routers on the path between a receiver and a sender. 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.
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 oob mechanism) before the application
starts running or applications that utilize some signaling to
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indicate the source address of the multicast stream (eg, electronic
programming guide 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 the designated
routers connected to receiving hosts to support IGMPv3 [RFC3376] and
MLDv2 [RFC3810]. Support for IGMPv3 and MLDv2 has become widespread
in common OSes for several years (Windows, MacOS, Linux/Android) and
is no longer an impediment to SSM deployment.
3.2. Advantages of SSM for interdomain multicast
A significant benefit of SSM is the reduced complexity that comes
through eliminating the network-based source discovery required in
ASM. Specifically, SSM eliminates the need for RPs, shared trees,
Shortest Path Tree (SPT) switchovers, PIM registers, MSDP, dynamic RP
discovery mechanisms (BSR/AutoRP) and data-driven state creation.
SSM simply utilizes 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 of multicast goes away.
This reduced complexity makes SSM radically simpler to manage,
troubleshoot and operate, particularly for backbone network
operators. This is the main motivation for the recommendation to
deprecate the use of ASM in interdomain scenarios. Note that SSM
operation is 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 inherently supports access
control. That is, receivers only get packets from the sources they
explicitly specify, as opposed to ASM where any host can send traffic
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to a group address and have it transmitted to all receivers. 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 support such interdomain applications fully support SSM and its
associated protocols. Best current practices for deploying
interdomain multicast using SSM are documented in [RFC8313].
The recommendation applies to the use of ASM between domains where
either MSDP (IPv4) or Embedded-RP (IPv6) is used.
An interdomain use of ASM multicast in the context of this document
is one where PIM-SM with RPs/MSDP/Embedded-RP is run on routers
operated by two or more separate administrative entities (domains,
organisations).
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).
4.2. Including network support for IGMPv3 / MLDv2
This document recommends that all hosts, router platforms and
security appliances supporting multicast 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].
Multicast snooping is often used limit the flooding of multicast
traffic in a layer 2 network. With snooping, a L2 switch will
monitor IGMP/MLD messages and only forward multicast traffic out host
ports that have interested receivers connected. Such snooping
capability should therefore support IGMPv3 and MLDv2. There is
further discussion in [RFC4541].
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4.3. Building application support for SSM
The recommendation to use SSM for interdomain multicast means that
applications should properly trigger the sending of IGMPv3/MLDv2
messages. It should be noted, however, there is a wide range of
applications today that only support ASM. In many cases this is due
to application developers being unaware of the operational concerns
of networks. This document serves to provide clear direction for
application developers to support SSM.
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."
Some useful considerations for multicast applications can be found in
[RFC3170].
4.4. Preferring SSM applications intradomain
If feasible, it is recommended for applications to 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, existing
intradomain PIM-SM networks are automatically compatible with SSM
applications. Thus, SSM applications can operate alongside existing
ASM applications. 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 source discovery, so intradomain ASM may still be
appropriate.
4.5. 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.
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There are existing vendor-specific mechanisms deployed that achieve
this function, but none are documented in IETF documents. This may
be a useful area for the IETF to work on as an interim transition
mechanism. However, these mechanisms would introduce additional
administrative burdens, along with the need for some form of address
management, neither of which are required in SSM. Hence, this should
not be considered a a long-term solution.
4.6. Not filtering ASM addressing between domains
A key benefit of SSM is that the receiver specifies the source-group
tuple when signaling interest in a multicast stream. Hence, the
group address need not be globally unique, so there is no need for
multicast address allocation as long the reserved SSM range is used.
Despite the deprecation of interdomain ASM, it is recommended that
operators should not filter ASM group ranges at domain boundaries, as
some form of ASM-SSM mappings may continue to be used for some time.
4.7. Not precluding Intradomain ASM
The use of ASM within a single multicast domain such as a campus or
enterprise 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
operational complexity. These existing practices are unaffected by
this document.
This document does not preclude continued use of ASM in the
intradomain scenario. If an organisation chooses to operate multiple
multicast domains within its own administrative borders, it may then
use MSDP or Embedded-RP internally within its own network.
5. Security Considerations
This document adds no new security considerations. It instead
removes security issues incurred by interdomain ASM with PIM-SM/MSDP
such as 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.
6. IANA Considerations
This document makes no request of IANA.
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Note to RFC Editor: this section may be removed upon publication as
an RFC.
7. 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.
8. References
8.1. Normative References
[RFC1112] Deering, S., "Host extensions for IP multicasting", STD 5,
RFC 1112, DOI 10.17487/RFC1112, August 1989,
<https://www.rfc-editor.org/info/rfc1112>.
[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>.
[RFC3307] Haberman, B., "Allocation Guidelines for IPv6 Multicast
Addresses", RFC 3307, DOI 10.17487/RFC3307, August 2002,
<https://www.rfc-editor.org/info/rfc3307>.
[RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version
3", RFC 3376, DOI 10.17487/RFC3376, October 2002,
<https://www.rfc-editor.org/info/rfc3376>.
[RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
DOI 10.17487/RFC3810, June 2004,
<https://www.rfc-editor.org/info/rfc3810>.
[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,
<https://www.rfc-editor.org/info/rfc3956>.
[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>.
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[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>.
[RFC4610] Farinacci, D. and Y. Cai, "Anycast-RP Using Protocol
Independent Multicast (PIM)", RFC 4610,
DOI 10.17487/RFC4610, August 2006,
<https://www.rfc-editor.org/info/rfc4610>.
[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,
<https://www.rfc-editor.org/info/rfc5771>.
[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>.
8.2. Informative References
[RFC2375] Hinden, R. and S. Deering, "IPv6 Multicast Address
Assignments", RFC 2375, DOI 10.17487/RFC2375, July 1998,
<https://www.rfc-editor.org/info/rfc2375>.
[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,
<https://www.rfc-editor.org/info/rfc3618>.
[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>.
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[RFC4541] Christensen, M., Kimball, K., and F. Solensky,
"Considerations for Internet Group Management Protocol
(IGMP) and Multicast Listener Discovery (MLD) Snooping
Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006,
<https://www.rfc-editor.org/info/rfc4541>.
[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,
<https://www.rfc-editor.org/info/rfc4609>.
[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,
<https://www.rfc-editor.org/info/rfc4611>.
[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,
<https://www.rfc-editor.org/info/rfc8313>.
[I-D.ietf-6man-rfc6434-bis]
Chown, T., Loughney, J., and T. Winters, "IPv6 Node
Requirements", draft-ietf-6man-rfc6434-bis-09 (work in
progress), July 2018.
Authors' Addresses
Mikael Abrahamsson
T-Systems
Stockholm
Sweden
Email: mikael.abrahamsson@t-systems.se
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Tim Chown
Jisc
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
Herndon, Virginia 20171
United States
Email: lenny@juniper.net
Toerless Eckert
Futurewei Technologies Inc.
2330 Central Expy
Santa Clara 95050
USA
Email: tte+ietf@cs.fau.de
Abrahamsson, et al. Expires April 25, 2019 [Page 13]