Re: [spring] We don't seem to be following our processes (Re: Network Programming - Penultimate Segment Popping)

Robert Raszuk <> Sat, 07 December 2019 11:47 UTC

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From: Robert Raszuk <>
Date: Sat, 7 Dec 2019 12:47:05 +0100
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To: Fernando Gont <>
Cc: Brian E Carpenter <>, Andrew Alston <>, Ole Troan <>, Ron Bonica <>, SPRING WG <>, 6man <>, "" <>, rtg-ads <>, Bob Hinden <>
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Subject: Re: [spring] We don't seem to be following our processes (Re: Network Programming - Penultimate Segment Popping)
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Hey Fernando,

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

I was trying to stay out of this but I have one fundamental question or
observation this entire debate seems to be about.

In the context of SRv6 there are two parallel discussions

*Discussion #1* - It is about inserting, modifying or deleting SRH by nodes
which are not in the outer IPv6 header of the packet

*Discussion #2* - It is about RFC8200 compliance when the node doing
insertion of SRH is *the* destination of the packet as read verbatim from
the outer IPv6 header.

*Discussion #3* - It is about RFC8200 compliance when the node doing
modification or removal of SRH is *the* destination of the packet as read
verbatim from the outer IPv6 header.

First let's observe that RFC8200 is only defining the behaviour regarding
EH processing in the context of destination address of the IPv6 outer
header: "identified in the Destination Address field of the IPv6
header.identified in the Destination Address field of the IPv6 header. "

Therefore stating that SL value before local decrement matters in this in
respect to being compliant to the IPv6 RFC is at best just an individual
interpretation. Besides the pseudocode says it black and white "S14.1.   If
(updated SL == 0) {". We do all sort of processing decision after
decrementing the values ... think TTL :)

So back to reality ...

*Discussion #1* - I think we all agree that to accomplish that RFC8200
would need to be updated.

*Discussion #2* - I think we also all agree here that to accomplish this
RFC8200 would need to be updated as it does says clearly that "Each
extension header should occur at most once, ..."

*Discussion #3* - It seems clearly that there is no issue with compliance
with RFC8200 and that if penultimate segment midpoint decides or is
instructed to pop SRH it sure can and still be 100% compliant with current
wording of RFC8200.

So other then so much foam what is this debate all about ?