Re: [spring] Penultimate Segment Popping and RFC8200 (Was Re: We don't seem to be following our processes (Re: Network Programming - Penultimate Segment Popping))

Brian E Carpenter <brian.e.carpenter@gmail.com> Sat, 07 December 2019 19:49 UTC

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To: "Ketan Talaulikar (ketant)" <ketant@cisco.com>, Suresh Krishnan <Suresh@kaloom.com>, Fernando Gont <fgont@si6networks.com>, SPRING WG <spring@ietf.org>
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From: Brian E Carpenter <brian.e.carpenter@gmail.com>
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Date: Sun, 8 Dec 2019 08:49:29 +1300
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Subject: Re: [spring] Penultimate Segment Popping and RFC8200 (Was Re: We don't seem to be following our processes (Re: Network Programming - Penultimate Segment Popping))
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Ketan,
On 07-Dec-19 23:13, Ketan Talaulikar (ketant) wrote:
> +1
> 
>  
> 
> For some strange reason the PSP behaviour is being mixed with EH insertion and likely there is some misunderstanding here.

I found the language in draft-ietf-spring-srv6-network-programming very hard to understand, and your comment and those from Robert Raszuk really don't clear it up. No insult intended, but it seems that SRH exponents are so close to SRH that you don't understand why others find it hard to understand.

So let me ask for clarification on three points in the draft. (Please keep me in CC as I'm not on the spring list.)

(1) Where the draft uses the word "insert", does it refer *only* to the encapsulating node at the SR domain ingress?

(2) What does the phrase ""Pop the SRH" mean? Does it mean "delete" a header inserted as in (1),
at the same time as decapsulating the packet?

(3) In *very* elementary language, what is "updated SL" in statement S14.2? It isn't defined elsewhere as far as I can see. It may just be sloppy writing, because if "Segments Left" is a variable, then perhaps "updated SL" just means the current value of "Segments Left" after executing S14.

With specific answers to those questions, the text would be easier to interpret.

Some diagrams of the encapsulation would be helpful, too.

Regards
   Brian

> 
>  
> 
> Fernando says:
> 
> 
> (pop when you are the destination but SL!=0 is essentially 'in the
> network removal’)
> 
>  
> 
> This is NOT what PSP is (refer https://tools.ietf.org/html/draft-ietf-spring-srv6-network-programming-05#section-4.16.1) – the “pop” is done when the SL becomes 0.
> 
>  
> 
> FWIW, this has been stated in different ways and clarified on the mailing list previously by the authors as well as others involved in SRv6 development and deployments. There is no violation of RFC8200 here.
> 
>  
> 
> Thanks,
> 
> Ketan
> 
>  
> 
> *From:*spring <spring-bounces@ietf.org>; *On Behalf Of *Suresh Krishnan
> *Sent:* 07 December 2019 12:50
> *To:* Fernando Gont <fgont@si6networks.com>;; SPRING WG <spring@ietf.org>;
> *Cc:* Ron Bonica <rbonica=40juniper.net@dmarc.ietf.org>;; int-ads@ietf.org; Andrew Alston <Andrew.Alston@liquidtelecom.com>;; rtg-ads <rtg-ads@ietf.org>;; Bob Hinden <bob.hinden@gmail.com>;; Ole Troan <otroan@employees.org>;; Brian E Carpenter <brian.e.carpenter@gmail.com>;
> *Subject:* [spring] Penultimate Segment Popping and RFC8200 (Was Re: We don't seem to be following our processes (Re: Network Programming - Penultimate Segment Popping))
> 
>  
> 
> (responding on spring mailing list)
> 
>  
> 
> Hi Fernando,
> 
> 
> 
>     On Dec 7, 2019, at 11:07 AM, Fernando Gont <fgont@si6networks.com <mailto:fgont@si6networks.com>> wrote:
> 
>      
> 
>     On 6/12/19 23:47, Brian E Carpenter wrote:
> 
>         Again, comment at the end...
>         On 07-Dec-19 14:37, Fernando Gont wrote:
> 
>             On 6/12/19 22:15, Brian E Carpenter wrote:
>             [...]
> 
> 
> 
>                     and if such a thing is required, an update to RFC8200 should be done.
> 
> 
>                 Why does that follow? Alternatively, draft-ietf-spring-srv6-network-programming could acknowledge that it deviates from RFC8200.
> 
> 
>             You can deviate from s "should", not from a "must". This is an outright
>             violation of a spec, rather than a mere "deviation".
> 
> 
> 
>                 Whether that's acceptable would be a question for the IETF Last Call rather than any single WG.
> 
> 
>             I would expect that a WG cannot ship a document that is violating an
>             existing spec, where the wg shipping the document is not in a position
>             of making decisions regarding the spec being violated.
> 
>             That would be like a waste of energy and time for all.
> 
> 
> 
> 
>                 At the moment, the draft only mentions RFC8200 in a context that discusses neither insertion nor removal of extension headers, which is beside the point. Like draft-voyer, if it describes a violation of RFC8200, shouldn't that be explicit in the text?
> 
>                 There's a lot of jargon in draft-ietf-spring-srv6-network-programming. I can't tell from the jargon whether "insert" means "insert on the fly" and whether "Pop the SRH" means "delete on the fly". Should those terms be clarified before the draft advances?
> 
> 
>             Well, if it's not clear to you, it would seem to me that the simple
>             answer would be "yes".
> 
> 
>         But if "insert" refers to the encapsulating node at the SR domain ingress, it's no problem, and if "pop" simply means doing normal routing header processing, it's no problem. It simply isn't clear in the text, at least not clear to me.
> 
> 
>     The fact that a folk that has been deeply involved with IPv6 cannot
>     unequivocally tell what they talking about should be an indication with
>     respect to how ready the document is to be shipped.
> 
>     (pop when you are the destination but SL!=0 is essentially 'in the
>     network removal’)
> 
>  
> 
> It is not obvious to me why you think this is a violation of RFC8200 though it is possible that I misread your comment. The relevant text I am looking at is
> 
>  
> 
> "  Extension headers (except for the Hop-by-Hop Options header) are not
> 
>    processed, inserted, or deleted by any node along a packet's delivery
> 
>    path, until the packet reaches the node (or each of the set of nodes,
> 
>    in the case of multicast) identified in the Destination Address field
> 
>    of the IPv6 header.”
> 
>  
> 
> which seems to permit it. Can you please clarify where there is a violation?
> 
>  
> 
> Regards
> 
> Suresh
>