Re: [Lsr] AD Review of draft-ietf-lsr-isis-rfc5306bis-02

Alvaro Retana <> Tue, 13 August 2019 18:48 UTC

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From: Alvaro Retana <>
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Date: Tue, 13 Aug 2019 11:48:00 -0700
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To: "Les Ginsberg (ginsberg)" <>, "" <>
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Subject: Re: [Lsr] AD Review of draft-ietf-lsr-isis-rfc5306bis-02
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On August 13, 2019 at 11:46:10 AM, Les Ginsberg (ginsberg) ( wrote:



245            Note: Implementations based on earlier drafts of RFC 5306

246            may not include this field in the TLV when the RA bit is set.

247            In this case, a router that is expecting an RA on a LAN

248            SHOULD assume that the acknowledgement is directed at the

249            system.

[major] I think it is time we stop catering to old/non-compliant
implementations.  The last time that a draft didn't include the System ID
was draft-ietf-isis-restart-03 in March 2003: more than 15 years ago!!

[Les:] While I am in sympathy with your position, the existing RFC has
allowed implementations based on early versions of the draft to exist and
defined how to interoperate with them. It is therefore conceivable that an
implementor simply never chose to update their implementation since they
never had an interoperability problem reported. I do not see the value in
removing this interoperability. The lack of this support would only be
meaningful in the event multiple systems on the same LAN were restarting at
the same time – which of course is possible but not probable. I will
continue to listen if you REALLY feel strongly about this, but in the
spirit of “being generous in what you receive” I left this unchanged.

We should have caught and eliminated the problem when rfc3874 was
published. <sigh>  BTW, the text above should mention rfc3874 and not

*[Les:] Well, I did ask where you were when RFC 3847 (not 3874 as I
mistakenly mentioned)  was approved. **😊*

<rant> IMO, catering to non-standard implementations in a formal
specification devalues the standards process: if the purpose is to create
interoperable implementations, but we’re still going to bend over backwards
to allow non-compliant implementations (with the product of the WG, the
consensus, etc.), then why are we going through the pain of agreeing on and
standardizing anything?  We might as well just let anyone implement
anything…or never change the original draft if specifications already
exist…  </rant>

In this case, making the System ID optional, and explaining how/when it
should be used (as you did above), would fix the issue and bring
non-compliant implementations into the fold.  IOW, I think we would all be
happy if the wording changed from “allow non-compliant implementations” to
“this field is optional”…for example:


   Required when the RA or PA bit is set. Otherwise

   this field SHOULD be omitted when sent and

   MUST be ignored when received.


   This field is required when the PA bit is set, and MAY be present when

   RA bit is set.  Specifically, it is used when multiple systems on the

   LAN are restarting {more details}. If the RA or PA bit is not set, this

   field SHOULD be omitted when sent and MUST be ignored when received.

*[Les:] There is no reason to extend this option to PA bit. Legacy issues –
if they exist at all - only exist in regards to RA. How about if I rewrite
the text with something like this?*

*“Very early draft versions of the restart functionality did not include
the Restarting Neighbor System ID in the TLV. RFC 5306 allowed for the
possibility of interoperating with these legacy implementations by*

*stating that a router that is expecting an RA on a LAN circuit  SHOULD
assume that the acknowledgement is directed at the local  system if the TLV
is received with RA set and Restarting Neighbor System ID is not present.*

*It is an implementation choice whether to continue to accept (on a LAN) a
TLV with RA set and Restarting Neighbor System ID absent. Note that the
omission of the Restarting Neighbor System ID only introduces ambiguity in
the case where there are multiple systems on a LAN*

*simultaneously performing restart.”*


Yes, that looks good…just to be extra picky about the rfc2119 keywords:
 s/SHOULD/should   It is not Normative in this document.

I’ll go ahead and start the IETF LC.  You can submit this change now, or as
other LC comments come in.