Re: [IPv6] Subject: Mandating SRH when using C-SIDs (draft-ietf-spring-srv6-srh-compression)

On Thu, 4 Apr 2024, 22:50 Francois Clad, <fclad.ietf@gmail.com> wrote:

> Hi Alvaro, all,
>
> RFC 8754 allows the SR source node to omit the SRH when it contains
> redundant information with what is already carried in the base IPv6 header.
> Mandating its presence for C-SID does not resolve any problem because it
> will not provide any extra information to the nodes along the packet path.
>

How are troubleshooting tools like 'tcpdump' going to know how to
automatically decode these packets as SRv6 packets if there is no SRH?

> Specifically for the case of middleboxes attempting to verify the
> upper-layer checksum,
>
>    - An SRv6-unaware middlebox will not be able to verify the upper-layer
>    checksum of SRv6 packets in flight, regardless of whether an SRH is present
>    or not.
>    - An SRv6 and C-SID aware middlebox will be able to find the ultimate
>    DA and verify the upper-layer checksum in flight, regardless of whether an
>    SRH is present or not.
>
>
> Furthermore, transit nodes (e.g., middleboxes) should not attempt to
> identify SRv6 traffic based on the presence of the SRH, because they will
> miss a significant portion of it: all the best-effort or Flex-Algo traffic
> steered with a single segment may not include an SRH, even without C-SID.
> Instead, RFC 8402, 8754, and 8986 define identification rules based on the
> SRv6 SID block.
>
> Thanks,
> Francois
>
>
> On 2 Apr 2024 at 19:44:51, Alvaro Retana <aretana.ietf@gmail.com> wrote:
>
>> [Moving this conversation up on your mailbox. :-) ]
>>
>> [Thanks, Robert and Tom for your input!]
>>
>>
>> We want to hear from more of you, including the authors. Even if you
>> already expressed your opinion in a different thread, please chime in here.
>>
>> We will collect feedback until the end of this week.
>>
>> Thanks!
>>
>> Alvaro.
>>
>> On March 28, 2024 at 8:06:18 AM, Alvaro Retana (aretana.ietf@gmail.com)
>> wrote:
>>
>>
>> Focusing on the C-SID draft, some have suggested requiring the presence
>> of the SRH whenever C-SIDs are used. Please discuss whether that is the
>> desired behavior (or not) -- please be specific when debating the benefits
>> or consequences of either behavior.
>>
>> Please keep the related (but independent) discussion of requiring the SRH
>> whenever SRv6 is used separate. This larger topic may impact several
>> documents and is better handled in a different thread (with 6man and spring
>> included).
>>
>> Thanks!
>>
>> Alvaro
>> -- for spring-chairs
>>
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