The MPLS WG Archive

[S Ramesh <rashanmu@npd.hcltech.com>]

Claus,

Please see inline

claus.bauer@tellabs.com wrote:

> The draft-ietf-mpls-lsp-hierarchy defines forwarding adjacencies and
> explains how these can be used to route LSPs within LSPs with higher
> switching granularity. Assuming an MPLS, not GMPLS network where the
> draft hierarchical LSP is not implemented, I got the following
> questions:
> LSPs can be tunneled through existing LSPs via label stacking.
> a. How do routers initiating an LSP know about the existence of these
> tunnels except by external means ? How can the available BW of the
> tunnel be known except by external means ?

In MPLS LSP tunnel is set up when there is request from a LSR ( downstream
on demand ) or pre-emptively by a LSR in the network ( downstream
unsolicitated ). The existence of the LSP tunnel can be known from the
forwarding table of the Ingress LSR initiating the LSP ( Control Driven
Model ). The available BW of the interface in which the LSP is established
can be known through a implementation which queries the Link Layer and
tells you the BW allocated and remaining on the interface.

>
> b. Assume a tunnel is known and an LSR initiating an LSP wants to route
> the LSP through the tunnel, how does the LSR starting the tunnel know
> that the LSP wants to be routed through this tunnel. From the ERO ?
>

A Ingress LSR initiating a LSP wants to send the flow through a specified
LSP ( besides the one present in the forwarding table for that flow )
means, it has to use the ERO object, specifying the LSP the flow has to
travel.

Thanks,
Ramesh

>
> Claus
>
>
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