Re: [pim] Call for adoption of sr-mpls-multicast-framework
Toerless Eckert <tte@cs.fau.de> Wed, 08 August 2018 20:14 UTC
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Date: Wed, 08 Aug 2018 22:14:45 +0200
From: Toerless Eckert <tte@cs.fau.de>
To: Michael McBride <Michael.McBride@huawei.com>
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Subject: Re: [pim] Call for adoption of sr-mpls-multicast-framework
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I do find this area of work very interesting, but I would prefer if the WG would not adopt this document yet. I would be happy to help/contribute (time permitting) with work in this area, but primarily when we can direct this work to: -> allow to support different forwarding planes -> Allow to support different signaling mechanisms -> concentrate on good specs for the centralized calculation/algos (even if that is maybe untypical IETF). Here are some issues i have with the current doc version: a) Target status I do not think a framework could/should be a standards track document. I think usually they are informative. b) Text quality - The document does not IMHO yet well enough explain the framework. It would help a lot to put some pictures into the document with topologies like what was presented at IETF102, and another with components and layers of the framework, and highlight the interactions better. - For example, the benefits and distinctions from existing solutions are not well summarized/explained, e.g: - minimizing number of nodes on a tree because - nodes do not support the scheme (not sure if this is considered - nodes not needed to do replication - calculating other than shortest path trees. Eg: there is no clear definition what a minimum cost tree is in this doc. It doesn't seem to be minimum spanning tree because that ha its root not necessarily in a PE. And it must be different from shortest path tree ? And its not steiner tree... ? c) Framework scope - In general, i would try to separate out the design of this framework from a particular choosen forwarding plane. To me, all the described mechanisms are quite independent of SR-MPLS, equally applicable to SRv6, classical MPLS, or equally IP tunneling & replication. I would really hate to have IETF invest into all the calculation schemes defined and then have that work tied up to just one forwarding plane plus maybe its son (SRv6). d) Centralized vs. distributed - The document tries to imply through the term "computing agent" that it can equally be performed centralized or cdecentralized/ distributed, but is quite vague about the details. - We have a bit the standardization issue in the IETF that IETF has not looked strongly into the algos when they are centralized because that does not require interoperability in consistent decision making. On the other hand, we also have some good but frustrating experience with distributed new path calculations like MRT. - In general, i will not believe right now whether or to what degree the results of a centralized path calculation approach using the ideas presented will achieve the same results as the distributed approach. If i am not mistaken, the example of MRT for example shows that in that particular case, the centralized result is better. - Personally, would prefer if a framework would first concentrate on being very specific to the centralized algorithms proposed to be used. Only when those are known can you IMHO well vet the option of a distributed version. Thats how it was done AFAIK on MRT (centralized algorithms known for decades?). Persistent loops or the like (disconnected trees ?). The document hints at some possible issues. - The frustrating experience from the MRT experience is of course also that vendors and industry do not seem to be willing or capable at this time to invest into intelligent distributed calculations. I blame the really bad and inagile software infrastructure in typical network equipment. Hence also the reccommendation to focus on the centralized specification approach first. e) Justification/comparisons -"This approach is proposed as a solution for networks for which an implementation of an alternative data plane, such as BIER, offers technical or economic challenges." There needs to be more justification text to support the necessity to invest into a framework. I would also like to see comparisons re. RSVP-TE, e.g.: what challenges would exist with that (the only one coming to mind is automatic transit over non-RSVP-TE P2MP nodes, but it would probably be easier to add that feature instead of reinventing a new scheme). - The IETF102 slides say that the solution utilizes SR-MPLS data plane in ways mLDP can not... didn't see representation/explanation of this claim in doc. f) Best WG ? - As outlined above, i think the mayority of the core framework work should be on the way how to calculate these (if i may call them that way) overlay trees, plus a bit the signaling schemes. I really doubt that PIM is the best WG to do this work. When writing up a framework for BIER-TE, Alia (back then AD) asked me to go to TEAS, claiming that TEAS should be responsible for all TE archticture/framework work. At least i think they could consult on what interfaces to design. The actual tree caluclation pieces... good question. RTWG would give it definitely more exposure and review than PIM, and especially when we'd take out the tie to a specific forwarding plane, that would also be a good logical place. Sorry for sounding like a Reichsbedenkentraeger (Royal Concern Officer), but better to bring up these issues now than in IESG review. Cheers Toerless On Mon, Aug 06, 2018 at 06:24:51PM +0000, Michael McBride wrote: > Hello good people, > > Today begins a two week call for adoption of draft-allan-pim-sr-mpls-multicast-framework-00 which was presented in Montreal. There was a good discussion in the meeting and now it's time to gauge interest in adoption on the list. Please respond and let us know what you think about adopting this draft.. > > https://tools.ietf.org/id/draft-allan-pim-sr-mpls-multicast-framework-00.txt > > thanks, > mike > _______________________________________________ > pim mailing list > pim@ietf.org > https://www.ietf.org/mailman/listinfo/pim
- [pim] Call for adoption of sr-mpls-multicast-fram… Michael McBride
- Re: [pim] Call for adoption of sr-mpls-multicast-… David Allan I
- Re: [pim] [**EXTERNAL**] Call for adoption of sr-… Duncan, Ian
- Re: [pim] Call for adoption of sr-mpls-multicast-… Jeff Tantsura
- Re: [pim] Call for adoption of sr-mpls-multicast-… Toerless Eckert
- Re: [pim] Call for adoption of sr-mpls-multicast-… Eric C Rosen
- Re: [pim] Call for adoption of sr-mpls-multicast-… David Allan I
- Re: [pim] Call for adoption of sr-mpls-multicast-… IJsbrand Wijnands
- Re: [pim] Call for adoption of sr-mpls-multicast-… John E Drake
- Re: [pim] Call for adoption of sr-mpls-multicast-… Greg Shepherd
- Re: [pim] [**EXTERNAL**] Re: Call for adoption of… Duncan, Ian
- Re: [pim] [**EXTERNAL**] Re: Call for adoption of… Michael McBride
- Re: [pim] Call for adoption of sr-mpls-multicast-… Uma Chunduri
- Re: [pim] Call for adoption of sr-mpls-multicast-… Jeffrey (Zhaohui) Zhang