Re: [spring] C-SIDs and upper layer checksums (draft-ietf-spring-srv6-srh-compression)

[Robert Raszuk <[e-mail]>]

Hi Ketan,


> a) SR Source Node: the node originating the packet - it may have an SRH or
> may skip it (section 4.1)
> b) Transit Node: node doing IPv6 forwarding
> c) (Ultimate) Destination Node (from RFC8200): the final node to which the
> packet is destined
>

All you said seems true valid, but the above three node categories do miss
a fourth one - randomly plugged sniffer, or any other way to selectively
capture subset of packets for troubleshooting.

I do think this is a bit of an obstacle to require that before such an
analyzer is connected to process live or offline traffic captures it needs
to be configured with given's network's SRv6 dedicated locator(s) and/or
SID blocks.

We clearly do not have such a requirement today for any other
transport protocol.

Maybe this is a good topic for SRv6OPS WG ? I said maybe as there clearly
seems to be a group of folks who say do not care about SRv6 or CSIDs and
would like to continue using same operational tools for troubleshooting
bare IPv6 protocol. Well in the network where both are running in parallel
lacking a clear demux flag seems to make it a bit of a challenge ...
especially if any endpoints talking native SRv6 with uSIDs would also talk
native IPv6.

Can you kindly share your perspective on this ?

Cheers,
Robert



> The CSID document in section 6.5 does not change or update the text in
> RFC8200 sec 8.1. It is simply stating what the "final destination" is going
> to be when CSID is used because RFC8200 does not talk about RHs in sec 8.1.
> RFC8754 covered this aspect by specifying that the last segment is the
> "final destination" but this needs to be specified when using C-SID (with
> or without SRH) and for all C-SID flavors/behaviors.
>
> I find the current text in section 6.5 to be necessary and sufficient for
> implementations that claim (or need to) support SR Source Node behavior for
> C-SIDs.
>
> The CSID document does not change any behavior at the Transit Node or for
> the (Ultimate) Destination Node. Therefore, the discussion of Transit Nodes
> is outside the scope of this document - just as it was outside the scope
> for RFC8754.
>
> Now, if some "Special Transit Node" wants to go beyond RFC8200 and do
> things like upper layer checksum validation enroute then they can refer to
> the same text in section 6.5 to first understand CSID processing and to do
> what is necessary for their packet processing enroute. This requires such
> "Special Transit Nodes" to be aware of first SRv6 and now C-SID - this is
> the same for any new packet encoding  technology.
>
> It seems like we are putting the cart before the horse when raising
> concerns about existing implementations that are not SRv6 and C-SID aware
> of not being able to do their processing. Let us publish the C-SID document
> so implementers of those "Special Transit Nodes" (also being referred to as
> middleboxes on some threads) have a reference to upgrade for C-SID support.
>
> Finally, I’ve not heard of issues related to these "Special Transit Nodes"
> from operators that have deployed SRv6. That may be a good discussion to
> have (again outside the scope of this document and perhaps in srv6ops?) -
> so operators who have SRv6 deployment experience can share their learnings
> and best practices.
>
> Thanks,
> Ketan
>
>
> On Thu, Mar 28, 2024 at 5:34 PM Alvaro Retana <[e-mail]>
> wrote:
>
>> Section 6.5 of draft-ietf-spring-srv6-srh-compression describes the
>> behavior when an originating node inside an SRv6 domain creates a
>> packet with a C-SID as the final destination. This description differs
>> from the text in Section 8.1 of RFC8200.
>>
>> We plan to send the draft to the 6man WG for review and explicitly
>> highlight this difference.
>>
>> Please comment on the text in Section 6.5. Does anything need to be
>> added, deleted, changed, or clarified?
>>
>> We want to ask for feedback soon; please send comments on this topic
>> by April 5th.
>>
>> Thanks!
>>
>> Alvaro.
>> -- for spring-chairs
>>
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