I know I posted about this before, and Giuseppe was very helpful. But still...
What really is the interplay between IS-IS and CLNS? There are claims in my books that IS-IS uses CLNS to transport its own routing info. In the real world, I know that IS-IS is its own Layer 3 protocol, separate from CLNP; and I also set up a tiny IS-IS environment in my lab in which two routers were configured with IS-IS routing and "ip router isis" on their interfaces. There were some loopbacks on one of the routers, and those loopback networks appeared in its neighbor's ip table as IS-IS routes (lowercase "i" on the left).
And when I did "show clns neighbors" I got a "%CLNS not running" message.
So it seems to me like IS-IS can get along fine without using CLNS at all. Or, did it work in the above case just because the routers were on the same broadcast medium? Do Level 2 routers need CLNS, since they do a fair amount of remote routing?
IS-IS is one of the scariest parts of the exam for me (along with IPv6, multicast routing, BGP prefix lists, route reflectors, regular expression, EIGRP query scoping, 6to4 tunneling...)