draft-ietf-mboned-deprecate-interdomain-asm-04.txt   draft-ietf-mboned-deprecate-interdomain-asm-05.txt 
Mboned M. Abrahamsson Mboned M. Abrahamsson
Internet-Draft T-Systems Internet-Draft T-Systems
Intended status: Best Current Practice T. Chown Intended status: Best Current Practice T. Chown
Expires: March 1, 2020 Jisc Expires: March 7, 2020 Jisc
L. Giuliano L. Giuliano
Juniper Networks, Inc. Juniper Networks, Inc.
T. Eckert T. Eckert
Huawei Huawei
August 29, 2019 September 4, 2019
Deprecating ASM for Interdomain Multicast Deprecating ASM for Interdomain Multicast
draft-ietf-mboned-deprecate-interdomain-asm-04 draft-ietf-mboned-deprecate-interdomain-asm-05
Abstract Abstract
This document recommends deprecation of the use of Any-Source This document recommends deprecation of the use of Any-Source
Multicast (ASM) for interdomain multicast. It recommends the use of Multicast (ASM) for interdomain multicast. It recommends the use of
Source-Specific Multicast (SSM) for interdomain multicast Source-Specific Multicast (SSM) for interdomain multicast
applications and that hosts and routers in these deployments fully applications and that hosts and routers in these deployments fully
support SSM. The recommendations in this document do not preclude support SSM. The recommendations in this document do not preclude
the continued use of ASM within a single organisation or domain and the continued use of ASM within a single organisation or domain and
are especially easy to adopt in existing intradomain ASM/PIM-SM are especially easy to adopt in existing intradomain ASM/PIM-SM
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 1, 2020. This Internet-Draft will expire on March 7, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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Bidir-PIM [RFC5015] is another protocol to support ASM. There is no Bidir-PIM [RFC5015] is another protocol to support ASM. There is no
standardized option to operate Bidir-PIM interdomain. It is deployed standardized option to operate Bidir-PIM interdomain. It is deployed
intradomain for applications where many sources send traffic to the intradomain for applications where many sources send traffic to the
same IP multicast groups because unlike PIM-SM it does not create same IP multicast groups because unlike PIM-SM it does not create
per-source state. Bidir-PIM is one of the important reasons for this per-source state. Bidir-PIM is one of the important reasons for this
document to not deprecate intradomain ASM. document to not deprecate intradomain ASM.
2.3. SSM Routing protocols 2.3. SSM Routing protocols
SSM is detailed in [RFC4607]. It mandates the use of PIM-SSM for SSM is detailed in [RFC4607]. It mandates the use of PIM-SSM for
routing of SSM. PIM-SSM as merely a subset of PIM-SM ([RFC7761]). routing of SSM. PIM-SSM is merely a subset of PIM-SM ([RFC7761]).
PIM-SSM expects that the sender's source address(es) is known in PIM-SSM expects that the sender's source address(es) is known in
advance by receivers through some out-of-band mechanism (typically in advance by receivers through some out-of-band mechanism (typically in
the application layer), and thus the receiver's designated router can the application layer), and thus the receiver's designated router can
send a PIM JOIN directly towards the source without needing to use an send a PIM JOIN directly towards the source without needing to use an
RP. RP.
IPv4 addresses in the 232/8 (232.0.0.0 to 232.255.255.255) range are 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 designated as source-specific multicast (SSM) destination addresses
and are reserved for use by source-specific applications and and are reserved for use by source-specific applications and
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This reduced complexity makes SSM radically simpler to manage, This reduced complexity makes SSM radically simpler to manage,
troubleshoot and operate, particularly for backbone network troubleshoot and operate, particularly for backbone network
operators. This is the main operator motivation for the operators. This is the main operator motivation for the
recommendation to deprecate the use of ASM in interdomain scenarios. recommendation to deprecate the use of ASM in interdomain scenarios.
Note that this discussion does not apply to Bidir-PIM, and there is Note that this discussion does not apply to Bidir-PIM, and there is
(as mentioned above) no standardized interdomain solution for Bidir- (as mentioned above) no standardized interdomain solution for Bidir-
PIM. In Bidir-PIM, traffic is forwarded to the RP instead of PIM. In Bidir-PIM, traffic is forwarded to the RP instead of
building state as in PIM-SM. This occurs even in the absence of building state as in PIM-SM. This occurs even in the absence of
receivers. Bidir-PIM therefore trades state complexity with receivers. Bidir-PIM therefore trades state complexity with
(potentially large amounts) of unnecessary traffic. unnecessary traffic (potentially a large amount).
3.2.2. No network wide IP multicast group-address management 3.2.2. No network wide IP multicast group-address management
In ASM, IP multicast group addresses need to be assigned to In ASM, IP multicast group addresses need to be assigned to
applications and instances thereof, so that two simultaneously active applications and instances thereof, so that two simultaneously active
application instances will not share the same group address and application instances will not share the same group address and
receive each others IP multicast traffic. receive each others IP multicast traffic.
In SSM, no such IP multicast group management is necessary. Instead, In SSM, no such IP multicast group management is necessary. Instead,
the IP multicast group address simply needs to be assigned locally on the IP multicast group address simply needs to be assigned locally on
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enterprise is still relatively common today. There are even global enterprise is still relatively common today. There are even global
enterprise networks that have successfully been using PIM-SM for many enterprise networks that have successfully been using PIM-SM for many
years. The operators of such networks most often use Anycast-RP years. The operators of such networks most often use Anycast-RP
[RFC4610] or MSDP (with IPv4) for RP resilience, at the expense of [RFC4610] or MSDP (with IPv4) for RP resilience, at the expense of
the extra operational complexity. These existing practices are the extra operational complexity. These existing practices are
unaffected by this document. unaffected by this document.
In the past decade, Bidir-PIM too has seen deployments to scale In the past decade, Bidir-PIM too has seen deployments to scale
interdomain ASM deployments beyond the capabilities of PIM-SM. This interdomain ASM deployments beyond the capabilities of PIM-SM. This
too is unaffected by this document, instead it is encouraged where too is unaffected by this document, instead it is encouraged where
necessary due to application requirements (see Section 4.4. necessary due to application requirements (see Section 4.4).
This document also does not preclude continued use of ASM with This document also does not preclude continued use of ASM with
multiple PIM-SM domains inside organisations, such as with IPv4 MSDP multiple PIM-SM domains inside organisations, such as with IPv4 MSDP
or IPv6 Embedded-RP. This includes organizations that are or IPv6 Embedded-RP. This includes organizations that are
federations and have appropriate, non-standardized mechanisms to deal federations and have appropriate, non-standardized mechanisms to deal
with the interdomain ASM issues explained in Section 3.2. with the interdomain ASM issues explained in Section 3.2.
4.9. Evolving PIM deployments for SSM 4.9. Evolving PIM deployments for SSM
Existing PIM-SM deployments can usually be used to run SSM Existing PIM-SM deployments can usually be used to run SSM
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Note that these migration recommendations do not include the Note that these migration recommendations do not include the
considerations when or how to evolve those intradomain applications considerations when or how to evolve those intradomain applications
best served by ASM/Bidir-PIM from PIM-SM to Bidir-PIM. This may also best served by ASM/Bidir-PIM from PIM-SM to Bidir-PIM. This may also
be important but is outside the scope of this document. be important but is outside the scope of this document.
5. Future interdomain ASM work 5. Future interdomain ASM work
Future work may attempt to overcome current limitations of ASM Future work may attempt to overcome current limitations of ASM
solutions, such as interdomain deployment solutions for Bidir-PIM, or solutions, such as interdomain deployment solutions for Bidir-PIM, or
source access control mechaisms for IPv6 PIM-SM with embedded-RP. source access control mechanisms for IPv6 PIM-SM with embedded-RP.
Such work could modify or amend the recommendations of this document Such work could modify or amend the recommendations of this document
(like any future IETF standards/BCP work). (like any future IETF standards/BCP work).
Nevertheless, it is very unlikely that any ASM solution, even with Nevertheless, it is very unlikely that any ASM solution, even with
such future work, can ever provide the same intrinsic security and such future work, can ever provide the same intrinsic security and
network and address management simplicity as SSM (see Section 3.2). network and address management simplicity as SSM (see Section 3.2).
Accordingly, this document recommends that future work for general Accordingly, this document recommends that future work for general
purpose interdomain IP multicast focus on SSM items listed in purpose interdomain IP multicast focus on SSM items listed in
Section 4. Section 4.
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