From: Tim (ccie2be@nyc.rr.com)
Date: Sun Aug 20 2006 - 11:20:11 ART
Hi guys,
I recently started trying to learn MPLS so I'm a complete newbie on the
topic.
I've been listening to the MPLS Essential VOD's on Cisco's PEC web site and
reading intro books on the technology.
However, there's a topic on which I'm very confused having to do with label
creation and distribution.
Suppose we have a very simple MPLS domain with 3 routers:
net-A rtr-1 net-B rtr-2 net-C rtr-3 net-D
Via the IGP, all routers learn about all subnets, A, B, C and D.
rtr-1 and rtr-3 and edge-LSR's and rtr-2 is just a plain LSR.
In this scenario, for which routes in the route table do the routers create
Labels?
Do they create labels for each route regardless of whether the route was
learned via the IGP or not; or for just the locally connected routes?
And, if it's for all routes, why is that?
For example, suppose rtr-1 creates a label for net-D. When would that label
ever be used?
On a related topic, how does a LSR decide what label to create? Does it
matter as long as the label is unique on the router creating the label?
Does the label have to certain characteristics to be a valid label?
Thanks in advance for any info that can be provided.
Tim
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