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

 Hi Mark,

Tcpdump/wireshark decodes the IPv6 header just fine. I do not see any issue
here.

Cheers,
Francois

On 4 Apr 2024 at 14:09:43, Mark Smith <markzzzsmith@gmail.com> wrote:

>
>
> 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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>