Subject: Re: [mpls] (no subject)

From: [email-masked]
Date: Mon, 18 Feb 2002 09:36:06 -0600

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 ?
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 ?

Claus

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Thank you.
Tellabs
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From: S Ramesh <[email-masked]>
Date: Mon, 18 Feb 2002 21:28:48 +0530

Claus,

Please see inline

> 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.

> 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