Subject: [spring] Mirja Kühlewind's No Objection on draft-ietf-spring-segment-routing-msdc-08: (with COMMENT)

From: Mirja Kühlewind <[email-masked]>
Date: Fri, 05 Jan 2018 07:30:36 -0800

Mirja Kühlewind has entered the following ballot position for
draft-ietf-spring-segment-routing-msdc-08: No Objection

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COMMENT:
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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?