[ns] MPLS rerouting problem

[Dan Wang <nsloam@yahoo.com>]

Hello everyone:

I'm quite confused about MPLS rerouting.
I tried the example /tcl/test-suite-mpls.tcl
the topology is

	         2----4----6
	      	/    /	  / \
               /    /    /   \    
	0-----1----3----5-----7-----8
		     
The packet will go through 0-1-3-5-7-8.
When the link 3~5 breaks down, the packets will
be sent from 3 back to the source and choose
another route to the destination. The full route
will be 0-1-3-1-2-4-6-7-8. This is fine. 

But when I change the broken link from 3~5 to 1~3, 
(I do not modify any other thing)
then, there will be a long time for the network to
probe and reconstruct the second route. But I think
the MPLS network should switch to the second route
immediately.

What's more, when I change the broken link from 3~5
to 5~7, the network will also probe for a long time
and reroute as 0-1-3-5-6-7-8. It does not choose
the route 0-1-3-5-3-1-2-4-6-7-8 as I expected.

I also imitated this example and wrote some other 
simple scripts but they does not work too. I read 
several MPLS documents and find that they are not 
detailed enough.

Any suggestion is appreciated.

Dan.

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