Subject: [Isis-wg] ISIS doubts.

From: ramanathan rams <[email-masked]>
Date: Wed, 18 Sep 2002 10:21:02 -0700

hi all,

I have some doubts in ISIS-TE, could u please explain me, also please let
me know if I am wrong with my assumptions.?

Assumptions :

*  In traffic engineering we usually specify the Explicit route for 
LSP(tunnel)
   establishment to the signalling protocol.

*  Link's traffic engineering attributes are distributed within the area
   for L1 and within L2 backbone for L2.

Doubts :

*  Using the domain wide prefix distribution standard, L2 information is
leaked inside the area and  L1 information is leaked outside the area. So
the path computed will have a best exit point( L1L2 router ) from that
area. ( from the exit point, L2 SPF is run and resulting inofrmation is
flooded within the area using  L1 LSPs ), for TE links how do L1L2
routers(exit points) compute the C-SPF( on what basis ) and flood the
information within the area using L1 LSP?

*  how do we get the full path( list of router's IP addresses ) which is
used for setting up the LSP, by running the C-SPF ? ( my assumption is that 
we can get information only till the exit router after that we don't know
about any routers which is present along the path to the destination) or
even the partial path till the exit point is enough for setting up LSP
tunnels?

How do we guarantee the specified constraints along the complete path of
the LSP using the ISIS-TE extension( because the TE information about the
links which are present in the other areas are not distributed throughout
the AS ) ?

* could u please briefly explain me how the Explicit path is calculated
with given constraints using ISIS TE & C-SPF to any destination which is
outside the source area in an ISIS AS( path calculation and TE database 
synchronisation which is used for explicit path calculation)?

thanks
rams.

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