Re: [spring] Question on draft-ietf-spring-srv6-network-programming-12

> On Mar 10, 2020, at 2:13 PM, Pablo Camarillo (pcamaril) <pcamaril=40cisco.com@dmarc.ietf.org> wrote:
> 
> Hi Chris,
> 
> Thanks for going through the document.
> The behaviors 4.13 (End.B6.Encaps), 4.14 (End.B6.Encaps.Red) and 4.15 (End.BM) correspond to Binding SIDs [1].
> 
> As a result of 4.13 for example, the packet is encapsulated with a new IPv6 header and an SRH that contains the SR policy associated to the BSID.
> Once the new IPv6 header is pushed into the packet, the NET-PGM pseudocode passes this packet to the IPv6 module of the router for transmission.
> 
> Normally the Upper-Layer Header should not be processed on a packet with a BSID, since you have just pushed an SR policy into the packet.
> That said, when the ultimate destination is BSID, then the Upper Layer Header processing is the same to End (4.1).
> 
> Hope it clarifies.

I'm still not clear on things I guess, but your answer leads me to a more basic question:

Section 4.1 described the basic "FIB entry" "End" which says:

  "When N receives a packet whose IPv6 DA is S and S is a local End SID, N does..."

So it's talking about a FIB entry for a "local End SID".

Section 4.1.1 says:

  "When processing the Upper-layer Header of a packet matching a FIB
   entry locally instantiated as an SRv6 End SID"

It's talking about a "FIB entry locally instantiated as an SRv6 END SID"

I'm not understanding how these 2 things are different. 4.1s calling a FIB Entry a "local End SID" 4.1.1 is calling something (different?) a "FIB Entry locally instantiated as an SRv6 END SID".

The terms seem too similar for me to make a distinction, where I feel the document expects me to make one.

Thanks,
Chris.

> 
> Thanks,
> Pablo.
> 
> [1]. https://tools.ietf.org/html/rfc8402#section-5
> 
> 
> -----Original Message-----
> From: spring <spring-bounces@ietf.org> on behalf of Christian Hopps <chopps@chopps.org>
> Date: Saturday, 7 March 2020 at 12:50
> To: "spring@ietf.org" <spring@ietf.org>
> Cc: Christian Hopps <chopps@chopps.org>
> Subject: [spring] Question on draft-ietf-spring-srv6-network-programming-12
> 
>    In sections 4.13, (implicitly in 4.14) and 4.15 a set of steps is indicated. As far as I can tell the processing of the IPv6 header chain in all cases is terminated. e.g.,
> 
>    "
>       When N receives a packet whose IPv6 DA is S and S is a local End.BM
>       SID, does:
> 
>      S01. When an SRH is processed {
>      S02.   If (Segments Left == 0) {
>    ....
>                   Interrupt packet processing and discard the packet.
>      S04.   }
>      S05.   If (IPv6 Hop Limit <= 1) {
>    ....
>                   Interrupt packet processing and discard the packet.
>      S07.   }
>      S09.   If ((Last Entry > max_LE) or (Segments Left > (Last Entry+1)) {
>    ....
>                   Interrupt packet processing and discard the packet.
>      S11.   }
>    ....
>      S15.   Submit the packet to the MPLS engine for transmission to the
>                topmost label.
>      S16. }
>    "
> 
>    The text then says:
> 
>       When processing the Upper-layer header of a packet matching a FIB
>       entry locally instantiated as an SRv6 End.BM SID, process the packet
>       as per Section 4.1.1.
> 
>    Why would I ever be processing the upper-layer header at this point?
> 
>    Thanks,
>    Chris.
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> 
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