[Lsr] more feedback on draft-ietf-lsr-isis-srv6-extensions-04

Chris Bowers <chrisbowers.ietf@gmail.com> Tue, 04 February 2020 23:29 UTC

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From: Chris Bowers <chrisbowers.ietf@gmail.com>
Date: Tue, 04 Feb 2020 17:27:06 -0600
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Subject: [Lsr] more feedback on draft-ietf-lsr-isis-srv6-extensions-04
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LSR,

I have some more feedback on draft-ietf-lsr-isis-srv6-extensions-04 that I
am putting in a separate thread so as not to confuse the other thread
related to N and A flags.

=======
The end of Section 5 points out several issues that can result in
forwarding not working correctly.  The reader might think that the next
section is going to discuss protocol mechanisms to avoid these issues.
Since this is not the case, I think it would be helpful to add some text
near the end of Section 5 like:

"In order to ensure correct forwarding, network operators should take steps
to make sure that this requirement is not compromised."


=========

In section 6, I think it would be useful to explicitly state the following
requirement for SRv6 Locator TLVs and their associated SRv6 SIDs:


"When anycast SRv6 Locator TLVs for the same prefix are advertised by
different nodes, the SRv6 Locator TLVs MUST all advertise identical sets of
SRv6 SIDs."


Section 3.3 of RFC 8402 has similar text: "Within an anycast group, all
routers in an SR domain MUST advertise the same prefix with the same SID
value."  That text only refers to a single SID value, so it seems somewhat
open to interpretation text in the context of an SRv6 locator that carries
multiple SRv6 SIDs. I think it would be better to avoid any potential
ambiguity by using the text proposed above in this document.

=========

In section 12.1.2.  "Revised sub-TLV table" it might avoid an extra
interaction with IANA to add a line for the flex-algo prefix metric
(currently 6) indicating "n" for TLV#27.

==========

Thanks,

Chris