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

"Pablo Camarillo (pcamaril)" <pcamaril@cisco.com> Tue, 10 March 2020 18:13 UTC

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From: "Pablo Camarillo (pcamaril)" <pcamaril@cisco.com>
To: Christian Hopps <chopps@chopps.org>
CC: "spring@ietf.org" <spring@ietf.org>
Thread-Topic: [spring] Question on draft-ietf-spring-srv6-network-programming-12
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Date: Tue, 10 Mar 2020 18:13:30 +0000
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Subject: Re: [spring] Question on draft-ietf-spring-srv6-network-programming-12
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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.

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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