Re: When is the ISIS attached bit set?

On Mon, Jul 23, 2012 at 10:06 PM, John Neiberger <jneiberger_at_gmail.com> wrote:
> I'm playing around with ISIS and I'm wondering about something that I
> hadn't really thought about much until now. If you have a mix of L2
> and L1 routers, the L2 routers will set the attached bit to advertise
> their candidacy for a default route. However, this only seems to
> happen if the L1/L2 router is attached to another area or detects an
> L2 router that is attached to another area.
>
> Does this mean that if we run single area ISIS, the L1/L2 routers will
> never set the attached bit and the L1 routers will not have a default
> route out to the rest of the network? If so, in situations like that
> it seems like it would just make more sense to run all one level.
>
> Thoughts?
>
> Thanks,
> John

Answering my own question, I took another look at default-information
originate in ISIS. By default, an L1/L2 router will only advertise the
default into L2. However, with the use of a route map, the
default-information originate command can be made to advertise it to
L1, as well.

route-map isis-default
 set level level-1-2

router isis 1
 default-information originate route-map isis-default

Regards,
John

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Received on Mon Jul 23 2012 - 22:28:27 ART