Deprecating ASM for Interdomain Multicast
Summary: Has enough positions to pass.
Warren Kumari Yes
Alvaro Retana Yes
Just a documentation nit: this document should be tagged in the Datatracker as replacing draft-acg-mboned-deprecate-interdomain-asm.
Deborah Brungard No Objection
Alissa Cooper No Objection
A couple of suggestions to help the document be more timeless: = Section 2.2.1 = s/To this day/At the time of this writing/ = Section 4.4 = OLD While the WG discussions had consensus that best practices should be developed to explain when to use SSM in applications, e.g, when ASM without (S,G) state in the network is better, or when dedicated service-discovery mechanisms should be used, it was agreed that documenting such practices are outside the scope of this document. NEW This document describes best practices to explain when to use SSM in applications, e.g, when ASM without (S,G) state in the network is better, or when dedicated service-discovery mechanisms should be used, but specifying these practices is outside the scope of this document.
Roman Danyliw No Objection
** Section 4.1. This section appears to provide multiple definitions of “separate administrative entities”. Per the paragraph “The more inclusive interpretation of this recommendation …”, it wasn’t clear to me under what circumstance the reader should use the more “inclusive interpretation”. ** Section 4. This section would benefit from being clearer on who should act on a few of the recommendation: -- Section 4.3 – vendors/developers of multicast applications? -- Section 4.4 – not clear who is supposed to develop this guidance? -- Section 4.6 – not clear who is supposed to developing this guidance long term ** Editorial Nits: -- Section 3.2.3. Typo. s/particularily/particularly/ -- Section 4.9. Typo. s/implentations/implementations/
Benjamin Kaduk No Objection
Thanks for this well-written document! Section 2.1 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 nit: "receivers" plural. Section 3.1 troubleshoot. Some of these issues include complex flooding Reverse Path Forwarding (RPF) rules, state attack protection, and filtering of undesired sources. I'm not sure how to parse "complex flooding Reverse Path Forwarding (RPF) rules" (but think I could figure out "complex Reverse Path Forwarding (RPF) flooding rules" -- do I need to try harder? 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 issue is one of biggest problems of interdomain multicast. Perhaps it's worth expanding on the security issue as including a substantial level of traffic amplification. (Or do I misunderstand the security issue?) Section 4.1 The more inclusive interpretation of this recommendation is that it also extends to deprecating use of ASM in the case where PIM is Are we claiming or disclaiming this "more inclusive interpretation"? The current wording feels ambiguous, and I don't think we should leave it that way. Section 4.2 support SSM (i.e., explicitly sending source-specific reports). The updated IPv6 Node Requirements RFC [I-D.ietf-6man-rfc6434-bis] states nit: the I-D reference is not yet an RFC, so it's not proper to refer to it as one; since it's only an informative reference we will not necessarily wait to publish this document until that one has an RFC number assigned, so I think this should be reworded. (Also, even if there was a new RFC number, "updated [...] RFC [RFCXXXX]" would still scan kind of strangely.) Section 4.3 The recommendation to use SSM for interdomain multicast means that applications should properly trigger the sending of IGMPv3/MLDv2 source-specific report 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. Without some discussion of the relative level of difficulty for applications tosupport SSM (to compare against the well-portrayed problems with network support for ASM), it would be fairly easy to misread this as network operators getting an IETF BCP to try to force applications to do what's easy for the network. I'm given to understand that's not actually the case here, as the changes in application software are fairly minor, and no one would expect existing applications to grow a way to announce multicast source addresses spontaneously, so a little more text might go a long way. Section 4.4 While the WG discussions had consensus that best practices should be developed to explain when to use SSM in applications, e.g, when ASM without (S,G) state in the network is better, or when dedicated service-discovery mechanisms should be used, it was agreed that documenting such practices are outside the scope of this document. It might be possible to rephrase this in terms of "the conclusions of the MBONED WG" or "the consensus of the MBONED WG"; the current phrasing feels a little informal to me, though I don't place much weight on my sentiment here. Section 4.6 A lot of this section feels somewhat speculative and leaves me uncertain what the BCP recommendations in this space are. 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 nit: I think this would read better with fewer commas, i.e., "to translate a (*,G) join or leave to a (S,G) join or leave for a specific source S". Section 4.9 it. This allows easy migration of ASM applications to SSM/PIM-SSM solely through application side development to handle source- nit: hyphenate "application-side". signaling via IGMPv3/MLDv2 and using SSM addresses. No network Do the application developers also consider this work "easy"? ;) When running PIM-SM, IGMPv3/MLDv2 (S,G) membership reports may also result in the desired PIM-SSM (S,G) operations and bypass any RP procedures, but this is not standardized but depends on implementation and may require additional configuration in available products. [...] nit: this sentence is fairly long and convoluted; could it be reworded and/or split up into smaller pieces? Note that these migration recommendations do not include the considerations when or how to evolve those intradomain applications 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. nit: is there a missing word ("for"/"about"/"on") after "considerations"? Accordingly, this document recommends that future work for general purpose interdomain IP multicast focus on SSM items listed in Section 4. nit: hyphenate "general-purpose". Section 6 We could perhaps consider mentioning again the consequences of infrastructure assuming that SSM-range addresses are always used for SSM, such as during the transition period where applications migrating from ASM to SSM continue to use ASM-range addresses, as mentioned in Section 4.7. Changing the model for intradomain multicast to one where source discovery/state-propagation is not done by the network and is instead a responsibility of the application layer means that the applications are responsible for properly implementing such functionality. While it's true that we do want applications to not have bugs in general (and that would hopefully go without saying), we might want to discuss the scope of potential issues if applications get this wrong. Could application bugs (or bugs in host-level IGMPv3 or MLDv2 implementations) specific to SSM usage lead to any worse problems than just "application traffic doesn't flow", e.g., state exhaustion in the network? Section 10.1 I'm not seeing any references to RFC 4610 that would qualify it as normative; if normative is indeed the proper status, perhaps additional citations are in order?
Suresh Krishnan No Objection
Mirja Kühlewind No Objection
Thanks for this well-written document. I'm by far no expert here but reading this document it sounds a bit like RFC3618 should be moved to historic... was that discussed? This document seem not to use normative RFC2119 language but I think could benefit from it. Was that considered?
Barry Leiba No Objection
Thanks for a very clear document that was an easy read. I just have a few very minor editorial suggestions, which need no specific reply: — Section 2.1 — Source discovery in SSM is handled by some out-of-band mechanism (i.e., the application layer) The “i.e.” seems a bit odd here to my eye. I’d suggest wording this without the parentheses altogether, thus: NEW Source discovery in SSM is handled by some out-of-band mechanism in the application layer END — Section 2.3 — PIM-SSM expects that the sender's source address(es) is known in advance by receivers The “is” sounds odd with “addresses”, and it’s always difficult to know what to do for number agreement with things such as “address(es)”. I suggest writing around the problem this way: NEW PIM-SSM expects the sender's source address(es) to be known in advance by receivers END — Section 3.2.2 — There needs to be a hyphen in “network-wide”. — Section 4.1 — This document recommends that the use of ASM is deprecated for interdomain multicast This needs subjunctive mood: “that the use of ASM be deprecated”.
Alexey Melnikov No Objection
Adam Roach No Objection
Thanks for this well-written and well-reasoned document. Given the rather limited knowledge I have of the nuts and bolts of how multicast works at the routing layer, I found the text clear and easy to follow.
Martin Vigoureux No Objection
Éric Vyncke No Objection
Thank you for the work put into this document. The document is really easy to read with a nice introduction. I trust the responsible AD and my routing colleagues on their evaluation whether it is reasonable, sensible and useful to deprecate ASM in interdomain deployments. Regards, -éric == COMMENTS == Mostly a DISCUSS but really trivial to fix, please refer to RFC 8174 in addition to RFC 2119. Also, AFAIK, Toerless is affiliated to Futurewei and not Huawei, please fix his affiliation in the header. == NITS == -- Section 2.3 -- Please use lowercase in IPv6 addresses.