Hi Alvaro and all,
I re-read section 6.5, it seems to be clear enough IMO, it also has link
towards section 9.2 (ICMP Error processing).I do agree with Ketan's email about
the methodology for splitting all nodes into those 3 categories (Source,
Transit, Destination). Indeed those concerns were about some transit nodes
(especially legacy, Special Transit Node as Ketan said) which may experience
issues with upper layer checksums and they also cannot deliver the behavior per
section 9.2. I have discussed such potential issue with some colleagues and
they told that for modern applications there such as eBPF based it is not an
issue at all to make correct checksum handling. I also found some public
references for that such as:
https://github.com/facebookincubator/katran/tree/main
(katran/lib/bpf/csum_helpers.h). But additional research and experiments are
needed. Anyway it is beyond the scope of this draft.
May be we can just mention about such possibility for non-SRv6 aware Special
Transit Nodes in 6.5 and that would be enough to inform implementers and
operators in advance.
SY,Boris
On Monday, April 8, 2024 at 07:06:12 PM GMT+3, Ketan Talaulikar
<[email protected]> wrote:
Hi Alvaro,
I find some level of confusion on the discussion threads and it might perhaps
be due to the inconsistent use of terminologies. It would help to use the
correct terminologies from RFC8754 (6man WG RFC) to bring clarity on what is
within the scope and what is beyond the scope of this document.
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
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 <[email protected]> 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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