[ssm] Comments draft-ietf-magma-snoop-11.txt (SSM)
Toerless Eckert <eckert@cisco.com> Mon, 17 May 2004 17:50 UTC
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Date: Mon, 17 May 2004 10:32:05 -0700
From: Toerless Eckert <eckert@cisco.com>
To: magma@ietf.org, ssm@ietf.org, mboned@ietf.org
Cc: mjc@tt.dk, karen.kimball@hp.com, fsolensky@WestRidgeNetworks.com
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Subject: [ssm] Comments draft-ietf-magma-snoop-11.txt (SSM)
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I would hereby like to express my opinion that subject draft MUST mentioned SSM explicitly (and provide appropriate detail) before progressing any further. Without mentioning ASM and SSM service model support explicitly, we will solely get yet another document that will not support SSM sufficiently anmore and given that SSM is recognized by mboned to be the one service model the IETF should focus further work on, it is unacceptable to over and over get the excuse of "oh well, the SSM support side can be done later in a different document". [ Cc'ed ssm and mboned working groups to alert them about this lack of right focus of that draft. Please keep replies to the Reply-To: magma@ietf.org, to avoid flooding three mailing lists with this. ] Specifically this is what i think is needed: SSM can be used in varying IPv4 address ranges, a decision as to limit it to specific address ranges (like only the default 232.0.0.0/8 ) has not been made (i would also oppose that). IGMP snooping switches on the other hand should be zero-config simply deployable devices that do not necessarily need to be configured to know L3 specifics like an SSM range. For this reason i would recommend that a default mode of operations of IGMPv3 switches is mandated which provides for SM-safe-reporting, meaning that receiver systems expecting to use SSM will not be impacted by (erroneous) receiver systems using ASM style membership reports on any addresses. Problem: Reporter 1 on port 1 sending an INCLUDE({S},G) IGMPv3 report, reporter 2 on port 2 sending an EXCLUDE({},G) IGMPv3 report. IGMP snooping switch builds aggregate state for G to report to upstream router(s). This aggregate state is (according to IGMPv3 specs) EXCLUDE({},G). If only this is reported, reporter 1 SSM application will fail because the router never receives any INCLUDE({S},G) reports. Solution: Define SSM-safe-reporting to be a condition for an IGMP snooping switch in which it ensures that all include({S},G) membership state will be reported correctly to router ports irrespective of exclude({..},G) reports. There are lots of alternatives on how a switch can do this, the most simple one is to pass on _all_ membership reports from hosts without suppressing any of them on ports connected to routers. That way in above example both the INCLUDE and EXCLUDE mode report would be seen by the router and if G is SSM, the router can correctly ignore the EXCLUDE mode report. There are alternatives on how to do SSM-safe-reporting which are more complex but provide more membership report suppression/aggregation towards router ports, but i think details of those should be left up for individual implementations. I would simply mandate that the default operations of an IGMP snooping switch must provide for SSM-safe-reporting without explicit manual configuration of the SSM range and without expecting SSM to be only operated on a well known SSM-range (IPv4). Obviously, this is only a problem for IPv4, as in IPv6 the SSM-range is well defined, MLD-snooping routers can thus rely on that range definition. And yes, i understand that this is only an informational document, but that's all we have. Hugh also does not mentiones snooping in draft-holbrook-idmr-igmpv3-ssm-06.txt. Thanks Toerless _______________________________________________ ssm mailing list ssm@ietf.org https://www1.ietf.org/mailman/listinfo/ssm
- [ssm] Comments draft-ietf-magma-snoop-11.txt (SSM) Toerless Eckert