Re: Updating to RFC6434 to deal with 8200-style header insertion by IPIP

"C. M. Heard" <heard@pobox.com> Thu, 02 November 2017 21:30 UTC

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From: "C. M. Heard" <heard@pobox.com>
Date: Thu, 2 Nov 2017 14:30:35 -0700
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Subject: Re: Updating to RFC6434 to deal with 8200-style header insertion by IPIP
To: 6man WG <ipv6@ietf.org>
Cc: Brian E Carpenter <brian.e.carpenter@gmail.com>, Michael Richardson <mcr+ietf@sandelman.ca>
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On Thu, Nov 2, 2017 at 12:33 PM, Brian E Carpenter <
brian.e.carpenter@gmail.com>; wrote:

> On 03/11/2017 04:26, C. M. Heard wrote:
> > On Thu, Nov 2, 2017, Michael Richardson <mcr+ietf@sandelman.ca>; wrote:
> >
> >>
> >> C. M. Heard <heard@pobox.com>; wrote:
> >>     > On Wed, 01 Nov 2017, Michael Richardson wrote:
> >>     >> Yet we skip other extension headers in order to find the ULP.
> >>
> >>     > Not so. An end node that encounters an unrecognized extension
> header
> >> is
> >>
> >> Both AH and IPIP are well known and recognized extension headers.
>
> AH is an extension header. "IPIP" isn't. It's Protocol 41, and Protocol 41
> is otherwise known as IPv6. (That's why it's also called IPPROTO_IPV6).
> In RFC8200 terms that makes it an "upper-layer header". Strictly speaking,
> RFC8200 doesn't specify what to do with an unrecognized upper-layer header.
>

Actually, it does, and the disposition is exactly the same as for an
unrecognzed
extension header. Both come under the heading of ICMP Code 1 ("unrecognized
Next Header type encountered").  See the second paragraph on page 9. Indeed,
it could hardly be done any other way, since it's not possible for a node
to tell
whether an unrecognized Next Header type represents an extension header
or an upper-layer header.

--cmh