If you’re following along with my IS-IS example, it seems it’s a bit more complex than I thought. I brought up R2 and R1 stopped working.

So far, I’ve set the priority on R3 to 99 so it becomes the DIS which lets R1 and R2 see all routes except each other’s. Going to pull out Doyle and read more but I’m dealing with a bit of a water problem in the house. More later.

BTW, R3 has to be the DIS because of that whole pseudonode thing, and IS-IS not having an NBMA type network. The DIS has to see all the other routers, and neither R1 or R2 have that luxury.