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Re: Extension Header Insertion

Brian E Carpenter <brian.e.carpenter@gmail.com> Tue, 10 December 2019 01:02 UTC

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Subject: Re: Extension Header Insertion
To: 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>
From: Brian E Carpenter <brian.e.carpenter@gmail.com>
Organization: University of Auckland
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Date: Tue, 10 Dec 2019 14:02:08 +1300
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On 09-Dec-19 22:33, Adrian Farrel wrote:
> Hi Ron,
> 
> I think we can jump to a quick answer on this because draft-ietf-spring-srv6-network-programming-05 says:
> 
>    We assume that the SRH may
>    be present multiple times inside each packet.
> 
> Thus we may assume that the proponents of Extension Header insertion do think that it is acceptable to insert a second routing header into a packet that already has one.
> 
> And 8200 is clear when it says:
>    Each extension header should occur at most once, except for the
>    Destination Options header, which should occur at most twice (once
>    before a Routing header and once before the upper-layer header).

That's "should", which in a non-RFC2119 document like RFC 8200, means "should".
It's not "must". So while I would prefer that the relevant SRH document justifies
the exception, there isn't a breach of a mandatory requirement.
  
> So draft-ietf-spring-srv6-network-programming-05 includes a false assumption which need to be either removed or secured through an update to 8200.
>  
> Ideally, I suppose, draft-ietf-6man-segment-routing-header would have contained the clarification that the SRH could be present multiple times 

Yes

> (updating 8200 as it went).

Unnecessary, IMHO.

    Brian

> 
>  
> 
> Cheers,
> 
> Adrian
> 
>  
> 
> *From:*ipv6 <ipv6-bounces@ietf.org> *On Behalf Of *Ron Bonica
> *Sent:* 09 December 2019 03:04
> *To:* 6man <6man@ietf.org>
> *Subject:* Extension Header Insertion
> 
>  
> 
> Folks,
> 
>  
> 
> This question is posed primarily to the proponents of Extension Header insertion.
> 
>  
> 
> Do you think that it is acceptable to insert a second routing header into a packet that already has one, so the resulting packet looks like the following:
> 
>  
> 
>   * IPv6 header
>   * SRH
>   * SRH
>   * Upper-layer header
> 
>  
> 
> Would this be common in TI-LFA?
> 
>  
> 
>                                                                       Ron
> 
>  
> 
>  
> 
> Juniper Business Use Only
> 
> 
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