The MPLS WG Archive

["Santosh Gupta" <santoshg@daewoo.dti.daewoo.co.kr>]

Hi Yoshihiro
    Please see the embedded comments.

> Ajithn,
>
>  > LSP-IDs become part of the "traffic engineering state" of the network.
So
>  > it is legitimate to define a CR-LSP, whose ingress is LER2,  stacking
or
>  > splicing with an existing CR-LSP whose ingress is LER1,  the latter
being
>  > specified by its LSP-ID.   The entity which does traffic engineering
can be
>  > thought of as "higher" than the LSR, and it knows these LSP-IDs.  At
that
>  > level, there is global (or, supra-local) knowledge.
>
>  > However, from the point of view of LSRs, local knowledge is sufficient.
>  > LSRs need to know only the LSP-IDs they participate in.
>
>  > In your example,  LER2 and LSR5 do not need to know the spliced/stacked
>  > CR-LSP's LSP-ID because all they do with it is, just pass it downward.
>  > That remains true as we go down the request path till we hit LSR3, for
>  > which it is intended.   So there is no need for non-participating LSRs
to
>  > be aware of the LSP-ID.
>
> There is an issue here on how an LSR that is not aware of the LSP-ID
> can determine who is the "downward" LSR for the LSP-ID.
>
> I think it depends on the FEC type used for the CR-LSP, that is,
> an opaque FEC should not be used in this case.  If we use a prefix FEC or
> host address FEC, the "downward" LSR can be determined based
> on the FEC information.

Who is supposed to be the "Downstream" peer is decided by the global (or,
supra-local) entity which has the knowledge of all the LSPs and the topology
of the network.
An Opaque FEC has to be used for CR-LSP(sec 4.10 in
draft-ietf-mpls-cr-ldp-03) since this feature is there only in CR-LDP and to
setup a CR-LSP it is compulsory.
One more issue that crops up at this point is that how is this type of LSP
to be setup. The initial scenario that we discussed was

                LER1 ------> LSR2-------->LSR3------>LSR4

                LER2-------->LSR5

Now suppose the scenario were like

                LER1 ------> LSR2-------->LSR3------>LSR4------>LSR6

                LER2-------->LSR5------->LSR7

and LSR7 was supposed to connect to LSR4. How is the new LSP to be setup?
The  global (or, supra-local) entity will inform only LER2 which will be
sending message to LSR5 which would in turn send the request to LSR7. Is
there any standard draft on how this is to be handled?

Santosh Gupta

>
> Yoshihiro Ohba
>
>
>  > -- Ajith
>
>