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Re: SRH insertion vs encapsulation (Re: Next steps on Extension Header Insertion)

Tom Herbert <tom@herbertland.com> Fri, 04 November 2016 17:41 UTC

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From: Tom Herbert <tom@herbertland.com>
Date: Fri, 04 Nov 2016 10:41:43 -0700
Message-ID: <CALx6S36wau10FSJ95j4XLWLu+gHANOzGr4OneC6hReTPxtMvfg@mail.gmail.com>
Subject: Re: SRH insertion vs encapsulation (Re: Next steps on Extension Header Insertion)
To: "Stefano Previdi (sprevidi)" <sprevidi@cisco.com>
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Cc: Fernando Gont <fgont@si6networks.com>, 6man WG <ipv6@ietf.org>, 神明達哉 <jinmei@wide.ad.jp>, Bob Hinden <bob.hinden@gmail.com>
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On Fri, Nov 4, 2016 at 10:01 AM, Stefano Previdi (sprevidi)
<sprevidi@cisco.com> wrote:
>
>> On Nov 4, 2016, at 5:03 PM, 神明達哉 <jinmei@wide.ad.jp> wrote:
>>
>> At Fri, 4 Nov 2016 11:16:34 +0000,
>> Tim Chown <Tim.Chown@jisc.ac.uk> wrote:
>>
>>>> Huh? The segment routing header is far from imaginary.
>>>
>>> But what do you deduce is really being specified in the SRH drafts?
>>>
>>> In draft-ietf-6man-segment-routing-header-02 it says in section 2.2:
>>> [...]
>>> which implies the SRH uses encapsulation, and doesn’t insert an EH
>>> in the existing header chain.
>>
>> My understanding is that actual implementations don't follow what's
>> written in the draft and do insert an SRH:
>> https://www.ietf.org/mail-archive/web/ipv6/current/msg24236.html
>
>
> In fact, there are implementations that do what’s written in the draft and also do header insertion for some use cases. The use cases applies to controlled environments where, typically, a EH is inserted at ingress and removed at egress. This is the reality of v6 segment routing implementations used over v6 infrastructure of some operators.
>
FWIW, the SR patches currently under review for Linux also do this. I
did point out the discussions about EH insertion happening on this
list, but I doubt that we would disallow patches based on that. My
recommendation was to put a big disclaimer in the documentation and
allow user to configure it with the assumption they know what they're
doing.

Tom

> s.
>
>
>
>> (And my understanding is that the desire of some people to make the
>> "actual" behavior explicitly standard-compliant is one major
>> background motivation of why we are having this thread.)
>
>>
>> --
>> JINMEI, Tatuya
>>
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