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

Hi Joel,

Please check revision 13 of this document that clarifies the PSP section.

About your last point:
For both SR-MPLS and SRv6, there are restrictions on the path to be used, in particular:
- the SR policy may only use SIDs instantiated on SR Endpoints.
- When computing the SR policy, there are additional restrictions to consider, such as the Maximum SID Depth (MSD) capability of nodes in the topology. (for SRv6, see section 4 of draft-ietf-lsr-isis-srv6-extensions).

Regards,
Pablo.

-----Original Message-----
From: "Joel M. Halpern" <jmh@joelhalpern.com>
Date: Tuesday, 10 March 2020 at 19:26
To: "Pablo Camarillo (pcamaril)" <pcamaril@cisco.com>
Cc: "spring@ietf.org" <spring@ietf.org>
Subject: Re: [spring] Question on draft-ietf-spring-srv6-network-programming-12

    Pablo, in your reply below you say that the text in 8200 is "crystal 
    clear".  It requires an interesting lens to find something "crystal 
    clear" about which so many people have expressed so much disagreement. 
    While a lawyer may claim to a judge that text in a contract is crystal 
    clear, it is almost always hyperbole.  That may be useful in other 
    contexts.  It is not useful here.

    As far as I can tell, the text allows the interpretation that the PSP 
    protagonists have reached.  It also allows other interpretations.  In 
    the absence of clarity, I can not claim that PSP biolates 8200.  But it 
    sure as heck is not "crystal clear".

    I also find the articulated use cases for PSP muddy.  And as far as I 
    can tell, if the use cases are accurate, then there is a need for 
    greater clarity in the underlying drafts (NP because I do not want to 
    try call back the base SRH document) about the restrictions on paths 
    that can be used.

    Yours,
    Joel

    On 3/10/2020 2:13 PM, Pablo Camarillo (pcamaril) 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.
    > 
    > 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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    >      spring@ietf.org
    >      https://www.ietf.org/mailman/listinfo/spring
    >      
    > 
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