Re: What if? [was Re: Extension Header Insertion]

Fernando Gont <fernando@gont.com.ar> Tue, 10 December 2019 22:55 UTC

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Subject: Re: What if? [was Re: Extension Header Insertion]
To: Brian E Carpenter <brian.e.carpenter@gmail.com>, adrian@olddog.co.uk, 'Ron Bonica' <rbonica=40juniper.net@dmarc.ietf.org>, '6man' <6man@ietf.org>
References: <BN7PR05MB5699D9BA988F96E2F41CD390AE580@BN7PR05MB5699.namprd05.prod.outlook.com> <00dc01d5ae73$c361b450$4a251cf0$@olddog.co.uk> <dbcdeb1a-0091-da2b-20df-d991e6c06091@gmail.com> <9bc47200-4fea-37ce-0ede-cbf6a5f70ea9@gmail.com>
From: Fernando Gont <fernando@gont.com.ar>
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Date: Tue, 10 Dec 2019 13:30:29 -0500
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On 9/12/19 20:21, Brian E Carpenter wrote:
> So, let's assume that two consecutive SRH headers are allowed in the same packet.
> 
> So the first one (an example from draft-ietf-6man-segment-routing-header-26) is:
> 
>        Segments Left=2
>        Last Entry=2
>        Flags=0
>        Tag=0
>        Segment List[0]=S3
>        Segment List[1]=S2
>        Segment List[2]=S1
> 
> and the second one is
> 
>        Segments Left=1
>        Last Entry=1
>        Flags=0
>        Tag=0
>        Segment List[0]=S4
>        Segment List[1]=S5
> 
> I made that up and it's obviously nonsense, but if this is allowed why aren't the rules for processing conflicting SRHs described in draft-ietf-6man-segment-routing-header-26? Do we need to recall it from the RFC Editor queue to be fixed?

It would seem to me that this is not allowed.

What would be the semantics of a packet with two SRHs?

P.S.: If it had been allowed, it would have been explicitly allowed in
the SRH draft. -- you can't explicitly forbid all the possible
combinations of things that people might come up with... and there's an
existing recommendation against sending multiple instances of EHs in
RFC8200.

Thanks,
-- 
Fernando Gont
e-mail: fernando@gont.com.ar || fgont@si6networks.com
PGP Fingerprint: 7809 84F5 322E 45C7 F1C9 3945 96EE A9EF D076 FFF1