Re: Extension Header Insertion

On Mon, Dec 9, 2019 at 1:34 AM Adrian Farrel <adrian@olddog.co.uk> wrote:
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> Hi Ron,
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>
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> I think we can jump to a quick answer on this because draft-ietf-spring-srv6-network-programming-05 says:
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>
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>    We assume that the SRH may
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>    be present multiple times inside each packet.
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> 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.
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>
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> And 8200 is clear when it says:
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>    Each extension header should occur at most once, except for the
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>    Destination Options header, which should occur at most twice (once
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>    before a Routing header and once before the upper-layer header).
>
Adrian,

It's probably arguable if that would be a SHOULD or a MUST requirement
in normative language. In either case, the expectation is that
different types of extension headers only appear once. It is
conceivable that some receiving implementations enforce this
assumption so that in the presence of multiple occurrences things
could fail (i.e. be conservative in what you send).

Note that encapsulation with EH instead of Eh insertion would avoid
multiple occurrences of EH within the same IP packet thereby
maintaining the expectation in RFC8200.

Tom

>
>
> 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.
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> Ideally, I suppose, draft-ietf-6man-segment-routing-header would have contained the clarification that the SRH could be present multiple times (updating 8200 as it went).
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> Cheers,
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> Adrian
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>
>
> 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,
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>
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> This question is posed primarily to the proponents of Extension Header insertion.
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>
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> 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:
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>
>
> IPv6 header
> SRH
> SRH
> Upper-layer header
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>
>
> Would this be common in TI-LFA?
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>
>
>                                                                       Ron
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>
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>
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>
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