Re: [spring] draft-ietf-spring-srv6-srh-compression

[Robert Raszuk <[e-mail]>]

Hi Greg,

Just one nit ...

> that reporting on-path telemetry can be done over the management plane

Just for clarity I did not mean to report on mgmt plane. Just like MPLS
networks were using IP data plane so here SRv6 networks are using IPv6 data
plane. So I would actually prefer not to use mgmt plane for reporting OAM
but regular data plane.

Best,
R.


On Fri, Feb 9, 2024 at 12:37 AM Greg Mirsky <[e-mail]> wrote:

> Hi Robert,
> thank you for your clarification. I agree with you that reporting on-path
> telemetry can be done over the management plane. I don't see any issues
> with using C-SID specific to use of a two-way active measurement protocol
> like STAMP.
>
> Regards,
> Greg
>
> On Thu, Feb 8, 2024 at 1:45 PM Robert Raszuk <[e-mail]> wrote:
>
>> Greg,
>>
>> The doubt here is not about test path which truley you are correct to be
>> useful MUST follow data plane of real user traffic, but node on the path
>> simply reporting the error or reporting the measurements to the collector.
>> Hence those packets can be just IPv6 (modulo some VPN where we would need
>> to identify such VPN within the payload of the reply).
>>
>> Do you see any issue with STAMP packets in networks using C-SIDs ? If so
>> can you kindly describe it in detail ?
>>
>> Many thx,
>> R.
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> On Thu, Feb 8, 2024 at 10:30 PM Greg Mirsky <[e-mail]>
>> wrote:
>>
>>> Hi Robert,
>>> could you clarify "can be used"? Is it MAY, SHOULD or MUST?
>>> If we use an active performance measurement protocol, e.g., STAMP, then
>>> it is expected that the path of the reflected STAMP test packet traverses
>>> the same set of nodes and links as the original STAMP test packet. Thus,
>>> the Session-Reflector must use encapsulation that ensures the path
>>> coroutedness for the reflected test packet, e.g., C-SIDs.
>>>
>>> Regards,
>>> Greg
>>>
>>> On Wed, Feb 7, 2024 at 4:14 AM Robert Raszuk <[e-mail]> wrote:
>>>
>>>> Hi,
>>>>
>>>> Actually for OAM responses in vast majority of cases vanilla IPv6
>>>> packets can be used.
>>>>
>>>> Kind regards,
>>>> R.
>>>>
>>>> On Wed, Feb 7, 2024, 10:58 Mark Smith <[e-mail]> wrote:
>>>>
>>>>>
>>>>>
>>>>> On Wed, 7 Feb 2024, 20:08 Robert Raszuk, <[e-mail]> wrote:
>>>>>
>>>>>> Hi Mark,
>>>>>>
>>>>>> >  however UDP and ICMPv6 would be for OAM per RFC 9269
>>>>>>
>>>>>> I do agree if we are talking about no SRH containing packets.
>>>>>>
>>>>>
>>>>> I think it would also occur with an SRH if a middlebox is ignoring the
>>>>> SRH EH (e.g. unaware of how to handle it, or ignoring some or all IPv6 EHs)
>>>>> and validating the pseudo-header checksum when the packet's current DA
>>>>> isn't the final one, which of course it may not be if the packet is
>>>>> somewhere where in flight between the origin SA and the final DA.
>>>>>
>>>>> For a middlebox to validate the L4 pseudo header checksum somewhere
>>>>> during flight, it would have to determine the final DA for the calculation
>>>>> by digging it out of the SRH rather than using the packet's current DA.
>>>>>
>>>>> Without an SRH the middlebox would have to process the C-SIDs in the
>>>>> packet's DA field until it could identify the final DA before then
>>>>> performing the L4 pseudo-header calculation and validation.
>>>>>
>>>>> The would be conditional on the SRv6 payload being TCP, UDP or ICMPv6
>>>>> and the middlebox being SRv6 aware (i.e. understand SRH when present) and
>>>>> SR configured to identify C-SID DAs (SRH'less).
>>>>>
>>>>> So I don't really see how including an SRH in OAM packets solves the
>>>>> problem unless the middlebox is SRv6 aware.
>>>>>
>>>>> And this is precisely why I said "vast majority of packets" not "all
>>>>>> packets"
>>>>>>
>>>>>
>>>>>> Glad that you nailed it on the list.
>>>>>>
>>>>>> Cheers,
>>>>>> R.
>>>>>>
>>>>>> PS. What Ron suggests is too big of a hammer. Instead I see no reason
>>>>>> why OAM packets should not contain SRH and resolve the nit that way.
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Wed, Feb 7, 2024 at 5:44 AM Mark Smith <[e-mail]>
>>>>>> wrote:
>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On Tue, 6 Feb 2024, 03:17 Robert Raszuk, <[e-mail]> wrote:
>>>>>>>
>>>>>>>> Hi Ron,
>>>>>>>>
>>>>>>>> Is there a problem ?
>>>>>>>>
>>>>>>>> If I read RFC8200 L4 checksum is computed by the packet *originator
>>>>>>>> and validated by the packet's ultimate receiver. *
>>>>>>>>
>>>>>>>> In all SPRING work to the best of my knowledge the vast majority of
>>>>>>>> packets are only encapsulated by transit nodes.
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> If the payload of the SRv6 packet is another IP packet or layer 2
>>>>>>> frame e.g. Ethernet, common for L2 and L3 VPNs, then the layer 4 checksum
>>>>>>> issue probably wouldn't occur, because those protocols don't include the
>>>>>>> IPv6 pseudo-header fields in their checksum calculations if they even have
>>>>>>> a checksum at all - RFC 2473 IPin IPv6 doesn't, and in GRE it is optional.
>>>>>>>
>>>>>>> However, if SRv6 was used to to directly carry an upper layer
>>>>>>> transport layer protocol PDU like UDP, TCP or ICMPv6, then that's when the
>>>>>>> checksum/middlebox issue arises, because they do include the IPv6
>>>>>>> pseudo-header in their checksum, which would therefore include the SRv6 SA
>>>>>>> and DAs.
>>>>>>>
>>>>>>> Not sure if TCP would be commonly carried directly in an SRv6
>>>>>>> packet, however UDP and ICMPv6 would be for OAM per RFC 9269.
>>>>>>>
>>>>>>> So your SRv6 L2 or L3 VPN might be able to carry customer traffic
>>>>>>> successfully through a middle box, however you may not be able to SRv6
>>>>>>> traceroute or ping across it successfully, or have ICMPv6 error
>>>>>>> successfully sent between SRv6 nodes.
>>>>>>>
>>>>>>> Regards,
>>>>>>> Mark.
>>>>>>>
>>>>>>>
>>>>>>>> Is there any formal mandate in any of the RFCs that an
>>>>>>>> encapsulating node must mangle the inner packet's L4 checksum ? I don't
>>>>>>>> think so but stand open to get my understanding corrected.
>>>>>>>>
>>>>>>>> Cheers,
>>>>>>>> Robert
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> On Mon, Feb 5, 2024 at 5:04 PM Ron Bonica <rbonica=
>>>>>>>> [e-mail]> wrote:
>>>>>>>>
>>>>>>>>> Folks,
>>>>>>>>>
>>>>>>>>> Has anyone proposed a solution to the L4 checksum problem that
>>>>>>>>> Andrew talks about?
>>>>>>>>>
>>>>>>>>>                                           Ron
>>>>>>>>>
>>>>>>>>> Juniper Business Use Only
>>>>>>>>> ------------------------------
>>>>>>>>> *From:* spring <[e-mail]> on behalf of Andrew
>>>>>>>>> Alston - IETF <andrew-ietf=[e-mail]>
>>>>>>>>> *Sent:* Monday, February 5, 2024 5:21 AM
>>>>>>>>> *To:* [e-mail] <[e-mail]>
>>>>>>>>> *Subject:* [spring] draft-ietf-spring-srv6-srh-compression
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> [External Email. Be cautious of content]
>>>>>>>>>
>>>>>>>>> Hi All,
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> (In capacity as a contributor and wearing no other hats)
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> At this point I cannot support progression of this document until
>>>>>>>>> the issues around the L4 Checksum have been resolved.  It’s been clearly
>>>>>>>>> stated in other emails on the list that in certain circumstances the
>>>>>>>>> behavior described in this document break the L4 checksum as defined in
>>>>>>>>> RFC8200.  This requires an update to RFC8200 to fix it – and I’m not sure
>>>>>>>>> that spring can update 8200 absent the consent of 6man, which I’m not sure
>>>>>>>>> has been asked for, nor am I sure that a spring document can update
>>>>>>>>> something like 8200 in an area so fundamental as the checksum without a
>>>>>>>>> -BIS, which would have to be done via 6man.  The L4 checksum issue though
>>>>>>>>> is real – and it cannot simply be ignored.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> I also have deep concerns that the compression document creates
>>>>>>>>> something that (in a similar way to SRv6) creates something that is
>>>>>>>>> completely non-conformant with RFC4291.  There are multiple references to
>>>>>>>>> this in draft-6man-sids, and should draft-6man-sids become an RFC I would
>>>>>>>>> argue that it should probably be a normative reference in this document –
>>>>>>>>> on the logic that this document relies on similar RFC4291 violations that
>>>>>>>>> srv6 itself does (and for the record, just because SRv6 itself violates
>>>>>>>>> RFC4291 as is clearly documented in draft-6man-sids – does not make it
>>>>>>>>> acceptable to do so in yet another draft without clear and unambiguously
>>>>>>>>> stating the deviations and ideally updating RFC4291 to allow for said
>>>>>>>>> deviations)
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> I believe these two issues alone are sufficient that to pass this
>>>>>>>>> document would create still further tensions about the relationship between
>>>>>>>>> SRv6 and IPv6 and lead to confusion.  As such – I believe these issues need
>>>>>>>>> to be adequately dealt with – and the solutions to them need to be approved
>>>>>>>>> by 6man as the working group that holds responsibility for ipv6 maintenance.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Thanks
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Andrew Alston
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Internal All Employees
>>>>>>>>> _______________________________________________
>>>>>>>>> spring mailing list
>>>>>>>>> [e-mail]
>>>>>>>>> https://www.ietf.org/mailman/listinfo/spring
>>>>>>>>>
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