[c-nsp] IS-IS: Ignore Attached Bit

[Mark Tinka]

On Thursday 24 July 2008 05:19:28 Asbjorn Hojmark - Lists 
wrote:

> > r(config)#router isis
> > r(config-router)#ignore-attached-bit
> > r(config-router)#
>
> When/why would you want to do that?

Just to add to what Shankar mentioned, in our particular 
case, we only use IS-IS to carry our infrastructure and 
Loopback addresses.

ALL customer prefixes (either from their own blocks or 
assigned from ours) are maintained in iBGP.

We hold full BGP tables on most of our edge routers. We 
don't run BGP in the core (core is based on MPLS 
forwarding), and the core are L1/L2 IS's strung together.

Ignoring the ATT bit ensures we do not send traffic to 
destinations BGP might not know about, only to drop 
it "higher up" in the network. Moreover, since we use IS-IS 
only for infrastructure and Loopback address reachability, 
those routes are specifically carried within the network - 
so no need for a default route.

Cheers,

Mark.
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