I took the "Do I know this already" quiz in Cisco's BSCI Exam Certification Guide, and one of the questions asked me to identify which statements were true about IS-IS. One of them was that all L2 routers must be contiguous, which I selected as true, and the answer key said it was wrong. Later on in the chapter it is stated that in fact L2 routers DO need to be contiguous (makes sense to me).
So don't they? WHY WHY WHY WHY WHY does Cisco Press publish exams to make people who are actually right think they're wrong?!?!
I also encountered the claim that all L1 routers within an area form adjacencies with each other; while only the DIS sends out LSP's. (Unlike in OSPF where they only get adjacent with the DR and BDR.) Well then why do non-DIS routers form adjacencies with each other? What exactly does adjacency mean in the IS-IS context?