Re: [Lsr] Mirja Kühlewind's No Objection on draft-ietf-isis-segment-routing-extensions-24: (with COMMENT)

Mirja Kuehlewind <ietf@kuehlewind.net> Tue, 14 May 2019 16:34 UTC

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From: Mirja Kuehlewind <ietf@kuehlewind.net>
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Date: Tue, 14 May 2019 18:34:36 +0200
Cc: The IESG <iesg@ietf.org>, "draft-ietf-isis-segment-routing-extensions@ietf.org" <draft-ietf-isis-segment-routing-extensions@ietf.org>, Christian Hopps <chopps@chopps.org>, Uma Chunduri <uma.chunduri@huawei.com>, "aretana.ietf@gmail.com" <aretana.ietf@gmail.com>, "lsr-chairs@ietf.org" <lsr-chairs@ietf.org>, "lsr@ietf.org" <lsr@ietf.org>
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To: "Les Ginsberg (ginsberg)" <ginsberg@cisco.com>
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Subject: Re: [Lsr] Mirja Kühlewind's No Objection on draft-ietf-isis-segment-routing-extensions-24: (with COMMENT)
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Hi Les,

Please see inline.

> On 14. May 2019, at 18:12, Les Ginsberg (ginsberg) <ginsberg@cisco.com> wrote:
> 
> Mirja -
> 
> Thanx for the review.
> Responses inline.
> 
>> -----Original Message-----
>> From: Mirja Kühlewind via Datatracker <noreply@ietf.org>
>> Sent: Tuesday, May 14, 2019 4:58 AM
>> To: The IESG <iesg@ietf.org>
>> Cc: draft-ietf-isis-segment-routing-extensions@ietf.org; Christian Hopps
>> <chopps@chopps.org>; Uma Chunduri <uma.chunduri@huawei.com>;
>> aretana.ietf@gmail.com; lsr-chairs@ietf.org; uma.chunduri@huawei.com;
>> lsr@ietf.org
>> Subject: Mirja Kühlewind's No Objection on draft-ietf-isis-segment-routing-
>> extensions-24: (with COMMENT)
>> 
>> Mirja Kühlewind has entered the following ballot position for
>> draft-ietf-isis-segment-routing-extensions-24: No Objection
>> 
>> When responding, please keep the subject line intact and reply to all
>> email addresses included in the To and CC lines. (Feel free to cut this
>> introductory paragraph, however.)
>> 
>> 
>> Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html
>> for more information about IESG DISCUSS and COMMENT positions.
>> 
>> 
>> The document, along with other ballot positions, can be found here:
>> https://datatracker.ietf.org/doc/draft-ietf-isis-segment-routing-extensions/
>> 
>> 
>> 
>> ----------------------------------------------------------------------
>> COMMENT:
>> ----------------------------------------------------------------------
>> 
>> A few comments/questions:
>> 
>> 1) For both the Prefix Segment Identifier and the Adjacency Segment
>> Identifier
>> sub-TLV it is not fully clear to me what the value field is used for when the
>> V-Flag is set. Can you further elaborate this in the draft or provide a
>> respective pointer?
>> 
> [Les:] https://tools.ietf.org/html/draft-ietf-isis-segment-routing-extensions-24#section-2.1.1.1 defines this.

I was assuming that it is defined somewhere. Maybe putting a ref in the doc that points at this draft could be good.
> 
>> 2) The F-Flag in Adjacency Segment Identifier sub-TLV and SID/Label Binding
>> TLV
>> is only one bit. I'm not expecting a new version of IP any time soon,
>> however,
>> maybe completely different address families could be useful as well. Not
>> sure
>> if only 1 bit is future-proof...?
>> 
> [Les:] This is a very forward looking comment. :-)
> 
> Seriously, if a new version of IP is invented there will be a LOT of protocol work required to support it. It is also not a given that MPLS would be supported for such a new IP version - so it isn't at all a given that these extensions (however modified) would apply.

I’m actually not sure because many protocols that need to cover IPv4 and IPv6 have already a longer field (or alternative would need a new extension for any new protocol anyway)…

> Also, changing the encoding now would be problematic for existing deployments (of which there are many) and I think we would have a hard time defining what an extensible encoding would be.

I was assuming this answer already, so…
> 
> I like to think we can deal with this when the time comes.
> Sound OK?

… I guess it’s fine.

> 
>> 3) Would it make sense to also discuss any risk of leaking information (e.g.
>> about the network topology) in the security consideration section?
>> 
> 
> [Les:] Prefix leaking is an established practice in IS-IS dating back to RFC 1195,  extended by RFC 5302, and not modified by this document.
> Note that the Security section already discusses the advertisement of information used to program the MPLS forwarding plane - which covers the additional sub-TLV information which would accompany leaked prefixes.

Adding a few sentences and pointers to the RFC you just listed could still be good!

Mirja


> 
>    Les
>