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

[Greg Mirsky <[e-mail]>]

Hi Robert,
I imagine that a management plane, e.g., IPFIX, can use the IPv6 dataplane
as the underlay.

Regards,
Greg

On Thu, Feb 8, 2024 at 3:45 PM Robert Raszuk <[e-mail]> wrote:

> 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
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>>>>>>>>>>
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