Subject: RE: Some questions(label space, NHLFE, ldp peers for an address p refix)

From: Steve Yao <[email-masked]>
Date: Mon, 8 Jan 2001 10:14:51 -0600

Josue,

I think your description is probably better and the first condition in the
draft can be removed.

- Steve  

> -----Original Message-----
> From: Josue Kuri [mailto:[email-masked]]
> Sent: Monday, January 08, 2001 2:42 AM
> To: Eric Miao;
> @[email-masked]@[email-masked]@cinna
> .enst.fr@c
> inna.enst.fr
> Cc: [email-masked];
> @[email-masked]@[email-masked]@cinna
> .enst.fr@c
> inna.enst.fr
> Subject: Re: Some questions(label space, NHLFE, ldp peers for 
> an address
> prefix)
> 
> 
> 
> 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).
> 
> 
> 
> Regards,
> 
> 	Josue
> 

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