[Tsv-art] draft-ietf-rtgwg-multisegment-sdwan-15 telechat Tsvart review

[Wesley Eddy via Datatracker <[e-mail]>]

Document: draft-ietf-rtgwg-multisegment-sdwan
Title: Multi-segment SD-WAN via Cloud DCs
Reviewer: Wesley Eddy
Review result: Almost Ready

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I don't think this is quite ready for 2 reasons:

1) Since an additional set of headers is required (outer IP + UDP + GENEVE w/
the MultiSeg-SDWAN option), there is an obvious effect on packet size.  Other
than one recommendation about using a truncated HMAC value to reduce packet
overhead, there doesn't seem to be any consideration around how fragmentation
will be avoided or how MTUs are configured or information on them propagates
within the different SD-WAN segments and tunneling protocols being stacked up. 
How are people doing this in practice, and are there some general guidelines
and advice that should be provided?  From a transport protocol perspective, I
think this is a big missing aspect to the document.

2) I didn't find the document very readable in the beginning / Introduction
section.  It improves significantly and is fine deeper into the document, but
the introduction is not helpful IMHO.  The "Net2Cloud" reference is useful, but
unfortunately, I found the introduction section of this particular RTGWG
document a bit hard to understand in terms of specific technical problems.  It
has very specific protocols, architectures, and traffic flows in mind, but
doesn't define them well, and expects the reader to just understand.  The first
paragraph jumps in discussing "SD-WAN" (without qualifying what specific
approaches or technologies for SD-WAN are meant, nor even explaining the
acronym).  I found the diagrams later in Section 3.1 & 3.2 useful, but it would
help earlier in the introduction to describe what is being discussed in terms
of the cloud gateway, CPEs, etc. and where these are located or what types of
connectivity, addressing, encryption, etc. exists between them.