Re: [Int-area] Is IPv6 End-to-End? R.I.P. Architecture? (Fwd: Errata #5933 for RFC8200)

[Mark Andrews <[e-mail]>]

> On 28 Feb 2020, at 10:00, Tom Herbert <[e-mail]> wrote:
> 
> On Thu, Feb 27, 2020 at 2:52 PM Joe Touch <[e-mail]> wrote:
>> 
>> FWIW - there are separable issues here:
>> 
>> - whether an IP header (or parts thereof) should be changed in transit
>> 
>> AFAICT, the answer has always been yes, but limited to the hopcount/ttl in the base header and hop-by-hop options in the options/extension headers.
>> 
>> - whether an IP header length can change in transit
>> 
>> I see no reason why it can't become smaller, but if it can become larger then PMTUD and PLPMTUD don't work.
>> 
>> So the question isn't just what is wanted, it's what is feasible.
>> 
> Joe,
> 
> Per the problem about making packets larger in the network, I'd point
> out that this is already common due to in-network tunneling. In any
> case, it's really the only interesting case here (as opposed to making
> packets smaller).

Encapsulation doesn’t make the packet larger.  It is no different to
talking a packet from a ethernet and pushing it out a PPP link.  The
Enclosing headers differ in sizes but the IPv6 packet remains the
same size.

The difference with encapsulation, from the non encapsulation cases, is
that PTBs are sent to the encapsulating node which has to synthesis a
PTB to the original (as far as the encapsulating node is concerned)
sender when they are received with the MTU reduced by the encapsulation
overhead and the encapsulation header removed from the PTB payload.  The
sender of the un-encapsulated packet sees PTB with a MTU which will allow
future packets pass both the encapsulating node and the node which generated
the PTB of the encapsulated packet and the packet headers it originally sent.

Mark

> Tom
> 
>> Joe
>> 
>> 
>> 
>> 
>> On 2020-02-27 14:07, Tom Herbert wrote:
>> 
>> Fernando,
>> 
>> I think we need to be careful that IETF is labeled as a collection of
>> inflexible architectural purists. We know that standards conformance
>> is voluntary and we haven't seen the last time that someone, possibly
>> even a major vendor, will circumvent the system for their own
>> purposes. IMO extension header insertion is a great example of that.
>> On one hand we have people quoting IPv6 saying that it isn't allowed
>> per RFC8200-- period! And on other side there are proponents that see
>> a real need for it and believe they have clear use case-- at one
>> presentation in IETF a proponent bluntly stated that regardless of any
>> discussion in IETF they're going to do it! IMO, what we haven't seen,
>> was a real attempt to resolve and work out the engineering issues.
>> That's not for lack of trying-- for instance I proposed a direction to
>> try for an engineering compromise in draft-herbert-6man-eh-attrib-00,
>> but saw little discussion on that.
>> 
>> Tom
>> 
>> On Thu, Feb 27, 2020 at 1:43 PM Fernando Gont <[e-mail]> wrote:
>> 
>> 
>> Folks,
>> 
>> If you haven't been following recent developments in the Spring WG, you
>> may be surprised about some of the work that is being pursued (or was
>> being pursued)-
>> 
>> Such work has included proposing that some IPv6 routers insert and
>> remove routing headers en-route to the final destination.
>> 
>> After many very heated and lengthy debates, some of this work was
>> dropped, but other remains (e.g. routers removing IPv6 EHs from packets
>> en-route to their final destination, part of what they call "PSP"). For
>> the most part, the proponents have argued that "we have implemented it,
>> and the industry wants it" -- as if we just have to rubberstamp what
>> they have done.
>> 
>> On the technical side, the proponents have argued that:
>> 
>>     If a packet employs source routing (and hence its Destination
>>     Address is modified en-route to direct the packet through each
>>     of these "waypoints"), then any of such "waypoint" routers are
>>     free to add or remove IPv6 extension headers at will. (No, not
>>     encap/decap, but rather add/remove EHs from the IPv6 header
>>     chain).
>> 
>> That seems to me like a very major deviation from what's supposed to be
>> our current "architecture", where IPv6 is an end to end protocol.
>> Besides, it should be obvious that removal/insertion of EHs en-route
>> error reporting (since host typically check that the ICMP errors they
>> receive correspond to something that they actually sent).
>> 
>> 
>> A number of us have raised this a number of times, and at least some of
>> us feel that our concerns are being ignored.
>> 
>> It would seem to me that these documents and decisions have a concrete
>> impact on our architecture, and that they are being pursued without any
>> proper oversight. There is also a widespread feeling that having one or
>> a few big vendors pushing these ideas might be playing a role here.
>> 
>> (See, for instance:
>> 
>> * https://mailarchive.ietf.org/arch/msg/ipv6/Er7LR_VrsJLko_QnqEKTXvPcpj4/
>> 
>> * https://mailarchive.ietf.org/arch/msg/ipv6/gG7Fbz0R030g55oW1mvckj0THwc/
>> )
>> 
>> What I would expect is that all thes major changes to our existing
>> architecture and protocols would only done by formally updating existing
>> standards *if* deemed appropriate, as opposed to just trying to sneak
>> changes "when nobody is watching", or by having very curious
>> interpretations of our protocols and standards.
>> 
>> I've raised the topic to our AD (Suresh), to the IAB, and on the arch-d
>> list before, but so far haven't been lucky or seen anything meaningful
>> happen in this area.
>> 
>> I have also submitted an errata to make RFC8200 even more clear on the
>> topic, but it remains unprocessed.
>> 
>> So my questions are:
>> 
>> * On the technical area:
>> 
>>  + Is IPv6 an End To End protocol?  Or is the IETF's stance that
>> routers are free to mangle with the packet structure as they please?
>> 
>>  + Was IPv6 designed that way? And if it wasn't, when/how was the
>> architecture changed?
>> 
>> 
>> * On the procedural area:
>> 
>>   + Where/how should IETF WGs seek for architecture-related advice?
>> 
>>   + What do do in situations like the above?  Wait and see how things
>>     evolve, and upon any formal decisions, just submit formal Appeals
>>     if deemed necessary?  (and after way too much energy consumed from
>>     everyone)
>> 
>>     I would have expected that as soon as these issues were raised,
>>     the offending text would be removed rightaway. But that wasn't
>>     the case. And when the changes did happen, it wasn't without
>>     an extraordinary waste of time and energy from all of us.
>>     For instance, any work on IPv6 header insertion/deletion wouldn't
>>     seem to fit within the charters of the 6man or spring wgs.
>> 
>> 
>>     FWIW, this is not the first instance of issues surrounding the same
>>     topic. It goes back to the rfc2460bis effort, when a similar set of
>>     folks (too many from one big vendor) got to have 6man ship
>>     what became RFC8200 with a noted "ambiguity", just to be able
>>     to have some playground for EH insertion/deletion. And we only got
>>     to improve on that during IETF LC:
>> 
>>    (see:
>> https://mailarchive.ietf.org/arch/msg/ipv6/Kp76SONpyqWneNgvtc8sh-fGAu0/)
>> 
>> 
>> Thoughts or advice on the technical and/or procedural aspects will be
>> appreciated.
>> 
>> Thanks!
>> 
>> Cheers,
>> Fernando
>> 
>> 
>> 
>> 
>> -------- Forwarded Message --------
>> Subject: Errata #5933 for RFC8200
>> Date: Thu, 27 Feb 2020 17:07:36 -0300
>> From: Fernando Gont <[e-mail]>
>> To: Suresh Krishnan <[e-mail]>
>> CC: [e-mail] <[e-mail]>
>> 
>> Suresh,
>> 
>> Two months ago I filled an errata on RFC8200 regarding the processing of
>> IPv6 extension headers. The errata is available here:
>> https://www.rfc-editor.org/errata/eid5933
>> 
>> While I believe that folks with a knowledge of Internet Protocols would
>> be able to interpret what is in RFC8200, given recent discussions on the
>> topic, and upon a re-read of the text, I believe a clarification is
>> warranted, such that we allow all sorts of curious interpretations of
>> the text.
>> 
>> I send a heads-up on the 6man mailing list
>> (https://mailarchive.ietf.org/arch/msg/ipv6/6MPs25WvSMD6vVT0ekaMYjAwM6c/),
>> and the proposed text received the review of at least Brian Carpenter,
>> Ron Bonica, and Mark Smith. Their reviews are available on such thread.
>> 
>> In the light that some folks seem to be pretending to leverage "the lack
>> of clarify" in RFC8200 (an Internet Standard) to violate it, I'd
>> appreciate that the reported errata be processed.
>> 
>> Processing the aforementioned errata is key to many of the discussions
>> this and other WGs are having.
>> 
>> Thanks,
>> --
>> Fernando Gont
>> SI6 Networks
>> e-mail: [e-mail]
>> PGP Fingerprint: 6666 31C6 D484 63B2 8FB1 E3C4 AE25 0D55 1D4E 7492
>> 
>> 
>> 
>> 
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Mark Andrews, ISC
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