The MPLS WG Archive

[Bora Akyol <akyol@pluris.com>]

There is no such mechanism. The assumption is that the network
operator knows how to configure their equipment and they know
their network.

Bora


>>>>> "James" == James Huang <James_Huang@Mitel.COM> writes:

    James> From: James Huang@MITEL on 01/24/2001 12:03 PM PST Hi
    James> Bora: Maybe I did not express my concern clear
    James> enough.  As you said, the LSP setup will fail when
    James> the egress LSR assigns an Implicit NULL label to the
    James> penultimate hop, if the penultinate hop does not
    James> support PHP.  So there should be some negotiation
    James> mechanism in LDP or RSVP/TE such that an egress
    James> router will know not to assign an Implicit NULL label
    James> to a penultimate hop that does not support PHP.  But
    James> I can not find such mechanism in the documents.

    James> -- James Huang





    James> Bora Akyol <akyol@pluris.com> on 01/23/2001 08:24:45
    James> PM

    James> To: James Huang/USA/Mitel@Mitel cc: mpls@UU.NET

    James> Subject: PHP negotiation




    James> You should also read the label encapsulation
    James> RFC. What happens is that the egress LSR assigns an
    James> (...) NULL label (I think it should be Implicit Null)
    James> to the penultimate hop, if penultimate hop does not
    James> support this, then LSP setup should fail.

    James> There was a LOOONG discussion on this sometime last
    James> year.

    James> Some people think this stuff is really clear. I think
    James> that it is in about three different RFCs, and someone
    James> needs to write a BCP that explains common usage and
    James> tricks that network operators that use MPLS should
    James> use.

    James> BTW, this question comes up about once a month on the
    James> list, maybe we should have an MPLS FAQ.

    James> Bora


>>>>> "James" == James Huang <James_Huang@Mitel.COM> writes:

    James> Hi all, The following paragraph is from Section
    James> 3.16. (Penultimate Hop Popping) of RFC3031.


    James> "Initial label distribution protocol negotiations
    James> MUST allow each LSR to determine whether its
    James> neighboring LSRS are capable of popping the label
    James> stack.  A LSR MUST NOT request a label distribution
    James> peer to pop the label stack unless it is capable of
    James> doing so."

    James> However, I can not find any mechanism in LDP/CR-LDP
    James> or RSVP-TE to accomplish this PHP negotiation.

    James> Am I missing something here?



    James> -- James Huang