When is the ISIS attached bit set?

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

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Received on Mon Jul 23 2012 - 22:06:20 ART