Re: [IPv6] WG Adoption call for Segment Routing Header encapsulation for Alternate Marking Method

[Giuseppe Fioccola <[e-mail]>]

Hi Gyan,
Thank you for your support!
Please find my replies inline tagged as [GF].

Regards,

Giuseppe


From: ipv6 <[e-mail]> On Behalf Of Gyan Mishra
Sent: Saturday, February 11, 2023 9:06 AM
To: Joel Halpern <[e-mail]>
Cc: 6man <[e-mail]>; SPRING WG List <[e-mail]>
Subject: Re: [IPv6] WG Adoption call for Segment Routing Header encapsulation for Alternate Marking Method

I support WG adoption.  The draft is clearly and succinctly written.

This draft will be very useful for SRv6 performance measurements for on path IOAM telemetry.

Few questions.

Is the use and operation of the FlowMonID identical to how it’s described in RFC 9343 and if so then it’s identical to the RFC 6437 20 bit IPv6 header Flow label which is based on the standard 5-tuple header keys used in RFC 6437 for stateless load balancing on stateful signaling.

At the bottom of Section 1 page 5 describes the Data Field format.  At the bottom it talks about how to guarantee uniqueness of the flow for disambiguating the flow and that is the purpose of the 5-tuple header key to identify and disambiguate the flow so it’s uniquely identified as done with RFC 6437 stateless load balancing.

[GF]: Yes, the FlowMonID is identical to how it is described in RFC 9343 but it is different from the Flow label, as also specified in RFC9343. We will clarify this point in this document as well.

Use or SRH Alt Mark TLV - top of page 6
.. looks like a typo in the last sentence

[GF]: Yes, we will fix it

Old text

Because SRv6 Is a routing header, destination options before the routing header are processed by each destination in the routing list.

New text

Because the SRv6 SRH is a routing header, destination options are processed by per RFC 8200 Section 4.1 Note 1 first destination that appears in the IPv6 destination address field plus subsequent destinations listed in the routing header.

[GF]: Good suggestion. We can replace it.

As mentioned by others this drafts leverages use of SRH used by SRV6, new SRH TLV used to encode the Alt Mark data fields to monitor every node along the SRH path.

This is much more cost effective and optimal then adding additional EH DOH or HBH to encode the Alt Mark which is significant overhead and use of SRH TLV is most optimal for the Alt Mark PM encoding.

[GF]: Agree.

For SRv6 compression CSID draft as SRH is not used for Next SID flavor as long as hops is less than 5 hops, which in many cases for loose hops that is the case, maybe the Alt Mark meta data can be stored in a 16 bit service SID LIB - Local SID  ID block for the PM on path telemetry.

https://datatracker.ietf.org/doc/draft-ietf-spring-srv6-srh-compression/

[GF]: Good point. We can mention this case in the document.

I think an Operational Considerations section would be a good idea as mentioned by others.

Thanks

Gyan
On Wed, Feb 1, 2023 at 7:44 PM Joel Halpern <[e-mail]<mailto:[e-mail]>> wrote:
This call is for the draft at:
https://datatracker.ietf.org/doc/draft-fz-spring-srv6-alt-mark

This email starts the WG adoption call for the subject draft (as
requested by the authors, with apologies from the WG chairs for how long
it has taken to kick this out.)  This call will run through the end of
the day on Feb 16.  Pleaes read the whole email as there are a few
points, and it is not that long.

Please comment on whether you think this topic is something you think
the spring WG should work, whether you think this draft is a good
starting point for such work, any issues or concerns you have, and
whether you would be willing to help be contributing and / or reviewing
the work if the WG does choose to work on it.

6man is copied for their information, as this is different from but
related to an extension header proposal in front of 6man.

Authors and named contributors, please confirm to the list that all
known, relevant, IPR has been disclosed.  If it has note, please remedy
this gap.

The spring chairs have noted one aspect of this draft that caught our
eye, and we would appreciate WG members who comment on the adoption to
consider, and if possible opine, on this.  As we read this draft, as
distinct from the related 6man extension header work, this causes the
recorded altmarks to only be updated at routers identified in the SRH
segment list.  (We presume this would include all identified points in a
compressed container.) We could not tell from the document what the
value was for this as distinct from getting the measurements at all
routers.  Do WG members understand and agree that it does have value?

As a lesser point, we consider that one quote in the draft is misleading
and will likely need to be reworded in the near future.  The draft say
"SRH TLV can also be used to encode the AltMark Data Fields for SRv6 and
to monitor every node along the SR path."  It is unclear if these was
intended to mean all routers (most of which would not see this TLV) or
if it was intended to refer to only those routers identified in the SRH,
in which case we presume it will be reworded.

Thank you,

Joel

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Gyan Mishra

Network Solutions Architect

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M 301 502-1347