From: MBONED < mboned-bounces@xxxxxxxx> On Behalf Of James A. (Jim) Stevens
Some background to Tim Chown's comment about "pushback in earlier discussions"
Section 4.4 is on Developing application guidance: SSM, ASM, service discovery
Section 4.5 is on Preferring SSM applications intradomain
We have intradomain applications with up to hundreds of nodes doing many to many multicast IP packet exchanges where the nodes can dynamically come and go. (Although most networks only contain 20 to 100 nodes, I believe the largest such network had >250 nodes
doing many to many multicast.
SSM is not feasible (and neither is ASM with PIM-SM due to the high overhead and dynamics as nodes come and go). So our applications use ASM with BIDIR-PIM.
We want to ensure that operating system and router developers continue to support ASM and BIDIR-PIM over the long term for our intradomain applications. I.e., we do NOT want to deprecate intradomain use of ASM.
Thus, we pushed back against the recommendation in 4.4 to develop new applications using SSM and in 4.5 to prefer SSM for future intradomain applications. In response, the draft-ietf-mboned-deprecate-interdomain-asm document was updated to put in the phrase
"if feasible" in sections 4.4. and 4.5 so that SSM is not recommended if not feasible.
Note that we do not object to deprecating interdomain use of ASM.
I would like to emphatically post a +1 here. On all points, except perhaps the use of PIM (for security reasons primarily).
As long as we're talking interdomain, no objections. But intradomain, the fact that the source of a given multicast might vary, without mandating that each destination join all possible source-specific multicasts individually, is a "feature" that we exploit.
The model is much the same as telephone conference calls. You send out the conference call number to all possible participants, but then you want to avoid the extra complication of requiring each one dialing in having to dial the number of each participant.
That would be quite laborious and unnecessary.
Just to confirm this is indeed the thrust of the draft, as per the 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 existing intradomain ASM/PIM-SM
deployments.“
And in 4.5:
"4.5. 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."
This wording was the result of comments received from those using ASM within their own networks.
Tim
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