Re: [Lsr] AD Review of draft-ietf-lsr-isis-srv6-extensions-11

Alvaro Retana <> Thu, 08 April 2021 22:17 UTC

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Subject: Re: [Lsr] AD Review of draft-ietf-lsr-isis-srv6-extensions-11
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I looked at -12.

I have a couple of nits/minor comments below.  There's only one
significant one related to the information that must be shared between
the Prefix Reachability TLV and the SRv6 Locator TLV: it is currently
phrased as an example.

We're also waiting of the resolution of the registry thread.  If that
results in not needed to add registries then you can address the
comments below with any other IETF LC comments.  Otherwise I'll wait
for an update.



[Line numbers from idnits.]

16	Abstract
25	   This documents updates [RFC7370] by modifying an existing registry.

[minor] s/[RFC7370]/RFC 7370
No references in the Abstract.

102	1.  Introduction
137	   This documents updates [RFC7370] by modifying an existing registry
138	   Section 11.1.2.

[nit] s/Section 11.1.2/(Section 11.1.2)

192	4.1.  Maximum Segments Left MSD Type

194	   The Maximum Segments Left MSD Type specifies the maximum value of the
195	   "Segments Left" field [RFC8754] in the SRH of a received packet
196	   before applying the Endpoint behavior associated with a SID.

[minor] s/specifies/signals

229	4.4.  Maximum End D MSD Type

231	   The Maximum End D MSD Type specifies the maximum number of SIDs
232	   present in an SRH when performing decapsulation.  These includes, but
233	   not limited to, End.DX6, End.DT4, End.DT46, End with USD, End.X with
234	   USD as defined in [RFC8986]).

[nit] s/[RFC8986])/[RFC8986]

243	5.  SRv6 SIDs and Reachability
263	   Locators associated with algorithm 0 and 1 (for all supported
264	   topologies) SHOULD be advertised in a Prefix Reachability TLV (236 or
265	   237) so that legacy routers (i.e., routers which do NOT support SRv6)
266	   will install a forwarding entry for algorithm 0 and 1 SRv6 traffic.

[minor] s/NOT/not
This is not an rfc2119 keyword -- and someone else will ask for the same thing.

268	   In cases where a locator advertisement is received in both a Prefix
269	   Reachability TLV and an SRv6 Locator TLV - (e.g. prefix, prefix-
270	   length, MTID all being equal and Algorithm being 0 in Locator TLV),
271	   the Prefix Reachability advertisement MUST be preferred when
272	   installing entries in the forwarding plane.  This is to prevent
273	   inconsistent forwarding entries between SRv6 capable and SRv6
274	   incapable routers.  Such preference of Prefix Reachability
275	   advertisement does not have any impact on the rest of the data
276	   advertised in the SRv6 Locator TLV.

[major] "e.g. prefix, prefix-length, MTID all being equal and
Algorithm being 0 in Locator TLV"

This text should not be an example because those are the fields that
should match.  Please make it clear: "The locator advertisement is
both TLVs is considered the same when the following fliends match..."
(or something like that with better words).

866	11.5.  Sub-Sub-TLVs for SID Sub-TLVs

868	   This document requests a new IANA registry be created under the IS-IS
869	   TLV Codepoints Registry to control the assignment of sub-TLV types
870	   for the SID Sub-TLVs specified in this document - Section 7.2,
871	   Section 8.1, Section 8.2.  The suggested name of the new registry is
872	   "sub-sub-TLVs for SRv6 End SID (5) (sub-TLV of TLVs 27, 135, 235, 236
873	   and 237) and SRv6 End.X SID (43)/SRv6 LAN End.X SID (44) (sub-TLVs of
874	   TLVs 27, 135, 235, 236 and 237)".  The registration procedure is
875	   "Expert Review" as defined in [RFC8126].  Guidance for the Designated
876	   Experts is provided in [RFC7370]The following assignments are made by
877	   this document:

[nit] s/[RFC7370]The/[RFC7370]. The

879	    Type   Description                          Encoding
880	                                                Reference
881	   ---------------------------------------------------------
882	    0      Reserved
883	    1      SRv6 SID Structure Sub-Sub-TLV       Section 9
884	    2-255  Unassigned

[major] The reference should be "[This Document]".