Subject: [Isis-wg] Doubt regarding IP Internal Reach TLV

From: "R Selvaraj" <[email-masked]>
Date: Mon, 21 May 2001 01:36:12 -0700

Hi,
Section 5.3.4 of RFC 1195 states that IP addresses within the routing domain reachable directly via one or more interfaces on the router should be encoded in the L1 LSP's IP Internal reachability TLV. reachability . Here, do we need to consider circuit level also. I mean, a L12 router while encoding its L1 LSP's IP Inernal Reachability TLV should it encode only all of its L1 circit's IP address and should not consider its L2 circuit's IP address at all.

I found some implementation, for L12 router, not encodeing L2 circuit's IP address in its L1 LSP's IP Internal Reach TLV.

It'll be helpful if I get clarified.

Thanks,
Selva.

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From: Jeff Parker <[email-masked]>
Date: Thu, 24 May 2001 09:57:20 -0400

> By the way, most implementations allow you to run ISIS on an 
> interface in "passive mode" saying: "don't exchange packets 
> (don't raise adjacencies) but advertise the IP of the 
> interface as IP Internal Reachability".
> 
> Omer
> 
> > I would like to know wheather a L12
> > router shall include its local L2 circits IP adress in its L1 LSP's
> > Internal Reach TLV and vice versa for its L2 LSP.
> >
> > Selva.

I thought the issue was that there was no point in advertising 
that you can reach a network if you have no evidence that you
can, in fact, reach the network.  Just because you are configured
and you have carrier doesn't mean that you can get there from
here.  

The existence of an IS-IS Adjacency on a link proves that
there is at least one other router under the delusion that 
it can reach the net in question.  Implementations use 
"passive" to bring in networks that do not have other IS-IS
routers on it: the assumption is that the administrator 
has performed extra due-diligence on the link, much as he
would with a static configuration.   

- jeff parker
- axiowave networks