Subject: [Isis-wg] External route addition!

From: Mohit Thakur <[email-masked]>
Date: Tue, 10 May 2005 10:14:26 +0200

Hi,

I have some basic doubts and would be helpful if anyone can clear them.

Lets take a simple network:

R1 ------ R2

Two routers R1 & R2 are connected and have IS-IS running on them (Level 1).

The routers will build up adjancencies with the hello packets when they 
are turned on. The LSPDatabase for R1 will have two LSPs one of router 
R1 (itself) and the other for router R2.

Now if any external route is added in the router R1 (lets say 
statically), R1 should add it in the LSPDB but in the R1's own LSP.
Now:

1) When external routes are added in R1, do they have to be associated 
to any circuit, initially?

After this, if i understand the protocol well (please correct me if i 
don't), when any external route is added, the LSP (non pseudonode, in 
this case LSP-L1) is generated and is sent to all the circuits. This LSP 
will have the tlv data field for external routes.

So to understand it properly:
2) The LSP will be generated on the addition of external routes. Are the 
  LSPs generated on the topological change and timer expiration itself?

3) Is the role of CSNP just to help maintain the same Database in all 
routers by sending the list of LSPs and we call it so called update?

Thanks for your time and your help also.

Mohit Thakur

R&D Trainee,
6WIND, France

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From: Abhishek Verma <[email-masked]>
Date: Tue, 10 May 2005 15:23:15 +0530

Hi Mohit,

Let me attempt to help you here.
 
> R1 (itself) and the other for router R2.

Yes, and a pseudonode LSP issued by whichever router is the DIS on
this circuit (assuming this to be on a LAN)

> statically), R1 should add it in the LSPDB but in the R1's own LSP.

You would add this static route in the LSDB only if you have
redistributed static routes into ISIS.

> to any circuit, initially?

No. I assume by 'circuit' you mean an interface over which ISIS is
running. No, you could add a static route over an interface which may
not be running ISIS.

> will have the tlv data field for external routes.

Yes.

> 2) The LSP will be generated on the addition of external routes. 

Yes

> Are the

Yes, LSPs are re-generated when topology changes/reachability changes/
and/or timer expirations.

> routers by sending the list of LSPs and we call it so called update?

Yes.

Thanks,
Abhishek.

-- 

--
Class of 2004
Institute of Technology, BHU
Varanasi, India