[multipathtcp] Alissa Cooper's Discuss on draft-ietf-mptcp-rfc6824bis-15: (with DISCUSS and COMMENT)

Alissa Cooper via Datatracker <noreply@ietf.org> Mon, 13 May 2019 20:22 UTC

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Subject: [multipathtcp] Alissa Cooper's Discuss on draft-ietf-mptcp-rfc6824bis-15: (with DISCUSS and COMMENT)
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Alissa Cooper has entered the following ballot position for
draft-ietf-mptcp-rfc6824bis-15: Discuss

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DISCUSS:
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I have a question about the interaction between the protocol versioning and the
way the flags B-H are defined. This doc specifies that B MUST be set to 0 and
that future specs might require it to be set to 1, which could alter the
meanings of the C-H flags. This is the same way that B is defined in RFC 6824.
This spec goes on to define C and H differently from how they are defined in
RFC 6824. Thus, both v0 and v1 implementations will have B set to 0, but they
will have C and H defined differently. I guess it depends on how you interpret
"extensibility flag," but my interpretation of this is that the version number
negotiated using MP_CAPABLE is the actual extensibility mechanism that this
specification is making use of, because although it changed C and H it did not
change B. Is this right?

If so, I'm wondering what the threshold is for defining new versions of this
protocol versus using this extensibility mechanism based on the B flag. Given
the way the version negotiation mechanism is defined -- requiring extra
round-trips in the event of a fallback attempt, and it being subject to a
downgrade attack -- I'm wondering if some guidance needs to be provided about
which sorts of protocol changes are expected to be made using the B-flag
mechanism versus using the version negotiation mechanism. I guess the drawback
of using the B-flag mechanism is that once a future spec sets it to 1, from
then on logic within implementations will be required to interpret potentially
multiple different semantics of C-H. I guess this potentially raises another
question, which is why the B flag isn't just deprecated given the addition of
the version negotiation mechanism.


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COMMENT:
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Section 3.7: s/the lost of MPTCP options/the loss of MPTCP options/

Appendix E should be titled "Changes from RFC 6824"