Silly ISIS Question.

["Michael Snyder" <msnyder@xxxxxxxxxxxxxxxxxxxxxx>]

I have a bunch of Level 2 routers connected to some Level 1 routers, all
in the same area.  I assumed that the level one routers would get passed
or figure it out for themselves that the level-1-2 neighbor should be
their default route.  
 
Guess I was thinking it would work like a ospf stub no summary or nssa
area, with the abr passing the route.
 
How do does the level 1 routers decide to use their level 1-2 neighbor
as a default route?