Re: [Int-dir] Intdir telechat review of draft-ietf-spring-srv6-network-programming-18

"Eric Vyncke (evyncke)" <evyncke@cisco.com> Wed, 16 September 2020 05:51 UTC

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From: "Eric Vyncke (evyncke)" <evyncke@cisco.com>
To: Brian Haberman <brian@innovationslab.net>, "int-dir@ietf.org" <int-dir@ietf.org>
CC: "last-call@ietf.org" <last-call@ietf.org>, "spring@ietf.org" <spring@ietf.org>, "draft-ietf-spring-srv6-network-programming.all@ietf.org" <draft-ietf-spring-srv6-network-programming.all@ietf.org>
Thread-Topic: [Int-dir] Intdir telechat review of draft-ietf-spring-srv6-network-programming-18
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Date: Wed, 16 Sep 2020 05:50:52 +0000
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Archived-At: <https://mailarchive.ietf.org/arch/msg/int-dir/FK_8tTlYh-MRleKzbd0vXb0kOb0>
Subject: Re: [Int-dir] Intdir telechat review of draft-ietf-spring-srv6-network-programming-18
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Brian,

Thank you for your detailed reviewed of this document in the framework on INT-DIR.

I will refer to your review for my ballot next week.

Regards

-éric

-----Original Message-----
From: Int-dir <int-dir-bounces@ietf.org> on behalf of Brian Haberman via Datatracker <noreply@ietf.org>
Reply-To: Brian Haberman <brian@innovationslab.net>
Date: Monday, 14 September 2020 at 20:51
To: "int-dir@ietf.org" <int-dir@ietf.org>
Cc: "last-call@ietf.org" <last-call@ietf.org>rg>, "spring@ietf.org" <spring@ietf.org>rg>, "draft-ietf-spring-srv6-network-programming.all@ietf.org" <draft-ietf-spring-srv6-network-programming.all@ietf.org>
Subject: [Int-dir] Intdir telechat review of draft-ietf-spring-srv6-network-programming-18

    Reviewer: Brian Haberman
    Review result: On the Right Track

    Section 3
    - - - - - - -

    The abbreviated description of the section is a bit confusing related to FIB
    lookup. This text:

       When an SRv6 SID is in the Destination Address field of an IPv6
       header of a packet, it is routed through an IPv6 network as an IPv6
       address.

       Its processing is defined in [RFC8754] section 4.3 and reproduced
       here as a reminder.

    makes it sound like all FIB lookups are being done on SIDs whereas the text in
    8754, section 4.3 is much clearer that the lookups occur on IPv6 addresses and
    that some may be SIDs.

    Section 3.1
    - - - - - -

       This document defines an SRv6 SID as consisting of LOC:FUNCT:ARG,
       where a locator (LOC) is encoded in the L most significant bits of
       the SID, followed by F bits of function (FUNCT) and A bits of
       arguments (ARG).  L, the locator length, is flexible, and an operator
       is free to use the locator length of their choice.  F and A may be
       any value as long as L+F+A <= 128.  When L+F+A is less than 128 then
       the remainder of the SID MUST be zero.

    Does a system outside of the SR Ingress Node need to discover L? If so, is it
    derived from seeing a FIB entry for LOC? How does the a system determine the
    length of F and A? By comparing FIB entries for LOC and LOC:FUNCT (that is what
    I infer from section 3.2)? The parsing rules seem incomplete and can lead to
    behavior that is non-deterministic. The same can be said for B:N.

    What are the guidelines for choosing LOC (or B)? Does this come strictly out of
    the unicast address space? ULA space? Does this spec support LOC being
    allocated out of multicast space?

    The following text seems rather limiting:

         The ARG value of a routed SID SHOULD remain constant among packets in
         a given flow.  Varying ARG values among packets in a flow may result
         in different ECMP hashing and cause re-ordering.

    If ARG needs to stay constant, does this limit the types of functions that can
    be implemented using this technique?

    Section 3.2
    - - - - - -

    The various paragraphs that describe “example deployments” really don’t belong
    in a standards track document. If they are needed to explain the approach, then
    the description of the approach is incomplete. The reader should not have to
    infer functionality by parsing example uses. If the examples remain, I suggest
    they be put in an informative appendix.

    What constitutes a “remote node”?

    Section 4
    - - - - -

    I would suggest either mentioning that these behaviors are managed via an IANA
    registry or I would add a forward pointer to the IANA Considerations section.

    Section 4.16.1.2
    - - - - - - - -

    The steps described to process the SRH (i.e., instruction S14.4) is different
    from the process described for SRH processing in RFC 8754, Section 4.3.1.1. RFC
    8754 seems to only create an SRH in an encapsulating header (i.e., no SRH
    insertion). Why does this draft specify SRH removal?

    Section 5.1
    - - - - - -

    What is the relationship between node N and the address T used as the source
    address of the encapsulating header?

    Section 6
    - - - - -

    This section could use some introductory text to explain what is meant by an
    Operation.

    Section 7
    - - - - -

    Is there a security issue if a SID is used as a source address?

    Should any part of the prefix being used for SIDs be advertised to external
    peers/networks?



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