Re: [spring] Non-final destination address (was Re: Penultimate Segment Popping and RFC8200 (Was Re: We don't seem to be following our processes (Re: Network Programming - Penultimate Segment Popping)))

Suresh Krishnan <> Fri, 13 December 2019 03:56 UTC

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From: Suresh Krishnan <>
To: Fernando Gont <>
CC: SPRING WG <>, Ron Bonica <>, "" <>, Andrew Alston <>, rtg-ads <>, Bob Hinden <>, Ole Troan <>, Brian E Carpenter <>
Thread-Topic: Non-final destination address (was Re: [spring] Penultimate Segment Popping and RFC8200 (Was Re: We don't seem to be following our processes (Re: Network Programming - Penultimate Segment Popping)))
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Date: Fri, 13 Dec 2019 03:56:49 +0000
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Subject: Re: [spring] Non-final destination address (was Re: Penultimate Segment Popping and RFC8200 (Was Re: We don't seem to be following our processes (Re: Network Programming - Penultimate Segment Popping)))
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Hi Fernando,

On Dec 11, 2019, at 7:22 PM, Fernando Gont <<>> wrote:

On 11/12/19 19:04, Suresh Krishnan wrote:
Hi Fernando,
 Answer inline.

On Dec 7, 2019, at 9:31 AM, Fernando Gont <<>> wrote:

On 7/12/19 04:19, Suresh Krishnan wrote:
(responding on spring mailing list)

Hi Fernando,

On Dec 7, 2019, at 11:07 AM, Fernando Gont <<>
<>> wrote:

On 6/12/19 23:47, Brian E Carpenter wrote:
Again, comment at the end...
On 07-Dec-19 14:37, Fernando Gont wrote:
On 6/12/19 22:15, Brian E Carpenter wrote:

and if such a thing is required, an update to RFC8200 should be done.

Why does that follow? Alternatively,
draft-ietf-spring-srv6-network-programming could acknowledge that
it deviates from RFC8200.

You can deviate from s "should", not from a "must". This is an outright
violation of a spec, rather than a mere "deviation".

Whether that's acceptable would be a question for the IETF Last
Call rather than any single WG.

I would expect that a WG cannot ship a document that is violating an
existing spec, where the wg shipping the document is not in a position
of making decisions regarding the spec being violated.

That would be like a waste of energy and time for all.

At the moment, the draft only mentions RFC8200 in a context that
discusses neither insertion nor removal of extension headers, which
is beside the point. Like draft-voyer, if it describes a violation
of RFC8200, shouldn't that be explicit in the text?

There's a lot of jargon in
draft-ietf-spring-srv6-network-programming. I can't tell from the
jargon whether "insert" means "insert on the fly" and whether "Pop
the SRH" means "delete on the fly". Should those terms be clarified
before the draft advances?

Well, if it's not clear to you, it would seem to me that the simple
answer would be "yes".

But if "insert" refers to the encapsulating node at the SR domain
ingress, it's no problem, and if "pop" simply means doing normal
routing header processing, it's no problem. It simply isn't clear in
the text, at least not clear to me.

The fact that a folk that has been deeply involved with IPv6 cannot
unequivocally tell what they talking about should be an indication with
respect to how ready the document is to be shipped.

(pop when you are the destination but SL!=0 is essentially 'in the
network removal’)

It is not obvious to me why you think this is a violation of RFC8200
though it is possible that I misread your comment. The relevant text I
am looking at is

"  Extension headers (except for the Hop-by-Hop Options header) are not
  processed, inserted, or deleted by any node along a packet's delivery
  path, until the packet reaches the node (or each of the set of nodes,
  in the case of multicast) identified in the Destination Address field
  of the IPv6 header.”

which seems to permit it. Can you please clarify where there is a

In the context of RFC8200, where the text you have quoted is present,
can you tell me which address other than that of the final destination
can be in the Destination Address of the packet?

RFC8200 *clearly* speaks about the possibility of the destination address not being the ultimate recipient in the presence of a Routing Header. This is from Section 3 defining the Destination Address as "128-bit address of the intended recipient of the packet (possibly not the ultimate recipient, if a Routing header is present).”

Section 4.4 says:
  The Routing header is used by an IPv6 source to list one or more
  intermediate nodes to be "visited" on the way to a packet's

(contrasts this to the statement with eh insertion/removal/processing)

While there could have been better use of terms, do you really think
that RFC8200 is allowing EH insertion/removal at waypoints? Or do you
think that, at best, the wording in RFC8200 could have been better?

For sure, I think the text in RFC8200 could have been more specific one way or another but it is impossible to tell at this point which direction the WG would have gone.