[spring] Mirja Kühlewind's Discuss on draft-ietf-spring-segment-routing-msdc-08: (with DISCUSS and COMMENT)
Mirja Kühlewind <ietf@kuehlewind.net> Thu, 11 January 2018 14:41 UTC
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From: Mirja Kühlewind <ietf@kuehlewind.net>
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Date: Thu, 11 Jan 2018 06:41:20 -0800
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Subject: [spring] Mirja Kühlewind's Discuss on draft-ietf-spring-segment-routing-msdc-08: (with DISCUSS and COMMENT)
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Mirja Kühlewind has entered the following ballot position for draft-ietf-spring-segment-routing-msdc-08: Discuss When responding, please keep the subject line intact and reply to all email addresses included in the To and CC lines. (Feel free to cut this introductory paragraph, however.) Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html for more information about IESG DISCUSS and COMMENT positions. The document, along with other ballot positions, can be found here: https://datatracker.ietf.org/doc/draft-ietf-spring-segment-routing-msdc/ ---------------------------------------------------------------------- DISCUSS: ---------------------------------------------------------------------- Sorry for the late input, but based on the additional TSV review provided by Martin Stiemerling (Thanks!), I got convenienced that I would like to discuss the TCP related parts of this document further before publication (even though this is "only" an informational doc). I agree with the TSV review that the solution approaches discussed in 7.1 and 7.2 are slightly speculative and should therefore probably not be published in an RFC without further discussions in respective other groups of the IETF. Per-packet/flowlet path switching (7.1) will have an impact on the TCP machinery and should be further discussed in a tsv group before it would be presented as a solution approach in an RFC. Performance-aware routing (7.2) is actually a hard problem as congestion state is changing very dynamically and an attempt to utilize this information on a different time-scale than TCP does can lead to unwanted interfere and interdependencies. We currently have a proposed research group (PANRG) for this sort of problems, and this group would probably a better place for discussing these problems and proposed solutions (instead of an RFC-to-be). The easiest way to address my concerns is probably to removed TCP-related paragraph from section 3 as well as remove section 7.1 and 7.2 entirely and follow on those discussions in tsv area/tcpm and panrg instead. ---------------------------------------------------------------------- COMMENT: ---------------------------------------------------------------------- I have a question regarding this part in section 3: "The absence of path visibility leaves transport protocols, such as TCP, with a "blackbox" view of the network. Some TCP metrics, such as SRTT, MSS, CWND and few others could be inferred and cached based on past history, but those apply to destinations, regardless of the path that has been chosen to get there. Thus, for instance, TCP is not capable of remembering "bad" paths, such as those that exhibited poor performance in the past. This means that every new connection will be established obliviously (memory- less) with regards to the paths chosen before, or chosen by other nodes." Is that actually a well-known problem? This is not fully clear to me. Because given that usually all paths in a data center network have roughly the same characteristics (at least regarding the cached values such as SRTT and MSS) caching of TCP parameters should not be a problem in symmetric topologies like Clos. Or do you have any specific corner cases in mind?
- [spring] Mirja Kühlewind's Discuss on draft-ietf-… Mirja Kühlewind
- Re: [spring] Mirja Kühlewind's Discuss on draft-i… Spencer Dawkins at IETF