So, I've tried to look at this with fresh eyes, and thanks for the
various updates and clarifications.
(I'm still not on the SPRING list so please leave me in CC.)
I remain a bit puzzled. First, a quote from the SRH specification
(draft-ietf-6man-segment-routing-header-26):
> 4.2. Transit Node
>
> As specified in [RFC8200], the only node allowed to inspect the
> Routing Extension Header (and therefore the SRH), is the node
> corresponding to the DA of the packet. Any other transit node MUST
> NOT inspect the underneath routing header and MUST forward the packet
> toward the DA according to its IPv6 routing table.
Next, a quote from the current draft:
> SRH[n]: A shorter representation of Segment List[n], as defined in
> [I-D.ietf-6man-segment-routing-header].
>
> When a packet is intercepted on a wire, it is possible that SRH[SL]
> is different from the DA.
Huh? That would be extremely unusual in the normal interpretation
of a routing header, where is RH[SL] is by definition the next
destination where the RH will be processed. Any other node is a transit
node, and I don't see anything in draft-ietf-6man-segment-routing-header-26
that allows for anything else. So it seems to me that the quoted statement
needs an explanation of why it isn't a violation of
draft-ietf-6man-segment-routing-header-26, not to mention why it's useful.
That leads us back to:
> 4.16.1. PSP: Penultimate Segment Pop of the SRH
>
> The SRH processing of the End, End.X and End.T behaviors are
> modified: after the instruction "S14. Update IPv6 DA with Segment
> List[Segments Left]" is executed, the following instructions must be
> executed as well:
>
> S14.1. If (Segments Left == 0) {
> S14.2. Update the Next Header field in the preceding header to the
> Next Header value of the SRH
> S14.3. Decrease the IPv6 header Payload Length by the Hdr Ext Len
> value of the SRH
> S14.4. Remove the SRH from the IPv6 extension header chain
> S14.5. }
This is clearly a breach of RFC8200, but it can never be reached if
DA == SRH[SL].
The operation "4.16.2. USP: Ultimate Segment Pop of the SRH" seems like
a pointless variant on "4.16.3. USD: Ultimate Segment Decapsulation",
since the packet has reached its destination anyway and will presumably
be decapsulated anyway.
Regards
Brian Carpenter
On 12-Dec-19 08:54, internet-dra...@ietf.org wrote:
>
> A New Internet-Draft is available from the on-line Internet-Drafts
> directories.
> This draft is a work item of the Source Packet Routing in Networking WG of
> the IETF.
>
> Title : SRv6 Network Programming
> Authors : Clarence Filsfils
> Pablo Camarillo Garvia
> John Leddy
> Daniel Voyer
> Satoru Matsushima
> Zhenbin Li
> Filename : draft-ietf-spring-srv6-network-programming-06.txt
> Pages : 39
> Date : 2019-12-11
>
> Abstract:
> The SRv6 Network Programming framework enables a network operator or
> an application to specify a packet packet processing program by
> encoding a sequence of instructions in the IPv6 packet header.
>
> Each instruction is implemented on one or several nodes in the
> network and identified by an SRv6 Segment Identifier in the packet.
>
> This document defines the SRv6 Network Programming concept and
> specifies the base set of SRv6 behaviors that enables the creation of
> interoperable overlays with underlay optimization (Service Level
> Agreements).
>
>
> The IETF datatracker status page for this draft is:
> https://datatracker.ietf.org/doc/draft-ietf-spring-srv6-network-programming/
>
> There are also htmlized versions available at:
> https://tools.ietf.org/html/draft-ietf-spring-srv6-network-programming-06
> https://datatracker.ietf.org/doc/html/draft-ietf-spring-srv6-network-programming-06
>
> A diff from the previous version is available at:
> https://www.ietf.org/rfcdiff?url2=draft-ietf-spring-srv6-network-programming-06
>
>
> Please note that it may take a couple of minutes from the time of submission
> until the htmlized version and diff are available at tools.ietf.org.
>
> Internet-Drafts are also available by anonymous FTP at:
> ftp://ftp.ietf.org/internet-drafts/
>
> _______________________________________________
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> Internet-Draft directories: http://www.ietf.org/shadow.html
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>
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