Subject: Re: Re: Some questions(label space, NHLFE, ldp peers for an address prefix)

From: Eric Miao <[email-masked]>
Date: Mon, 8 Jan 2001 18:54:20 +0800

>Hi Eric,
>
>> 1. Label Space
>> ==============
>> 
>> <draft-ietf-mpls-arch-07> 3.14. Scope and Uniqueness of Labels says
>> 
>>      In general, Rd can only tell whether it was Ru1 or Ru2 that put the
>>      particular label value L at the top of the label stack if the
>>      following conditions hold:
>> 
>>         - Ru1 and Ru2 are the only label distribution peers to which Rd
>>                               ~~~~
>>           distributed a binding of label value L, and
>>         - Ru1 and Ru2 are each directly connected to Rd via a point-to-
>>                                                               ~~~~~~~~~
>>           point interface.
>>           ~~~~~
>> 
>>      When these conditions hold, an LSR may use labels that have "per
>>      interface" scope, i.e., which are only unique per interface.  We may
>>      say that the LSR is using a "per-interface label space".  When these
>>      conditions do not hold, the labels must be unique over the LSR which
>>      has assigned them, and we may say that the LSR is using a "per-
>>      platform label space."
>> 
>> Why must Ru1 and Ru2 be only label distribution peers to which Rd distributed a
>> binding of label value L, and be each directly connected to Rd via a p2p interface?
>> 
>
>You can think about this otherwise:
>Rd distributes label "L".
>{Ru1, Ru2, Ru3...RuN} is a set of upstream LSRs (peers of Rd). If Rd
>has distributed the SAME label value "L" to all the LSRs in the set, when
>a packet with label "L" arrives to Rd, Rd can determine which LSR in the
>set sent the packet based on the interface the packet came through. Note
>that this is possible only if each LSR in the set is connected to Rd by a
>DIFFERENT interface.
>
>
>> 2. NHLFE
>> ========
>> 
>> <draft-ietf-mpls-arch-07> 3.10. The Next Hop Label Forwarding Entry (NHLFE) says
>> 
>>    the operation to perform on the packet's label stack; this is
>>    one of the following operations:
>>           a) replace the label at the top of the label stack with a
>>              specified new label
>>           b) pop the label stack
>>           c) replace the label at the top of the label stack with a
>>              specified new label, and then push one or more specified
>                                             ^^^^
>>              new labels onto the label stack.
>> 
>> Since there is FEC to NHLFE map (FTN) which determines what label an unlabeled packet
>> should be labeled with, why no  PUSH operation in NHLFE.
>> 
>
>There is a push operation in (c).
a) SWAP
b) POP
c) SWAP and PUSHes, not PUSHes

>Regards,
>	Josue

            Eric Miao
            [email-masked]