Been reading Doyvle V1 IS-IS chapter. Also been reading the PDF on cisco's web site regarding IS-IS.
Some questions based on this reading. 1) Why is it that the IS-IS model of having the router be in only a single area, as opposed to where an OSPF router can be in multiple areas results in significantly fewer LSPs? This reason is than used to suggest that IS-IS has better scaling properties than OSPF. It might, I'm just trying to understand why the different area demarc location would result in fewer LSA-type advertisements. If, in OSPF, any ABR router was limited to be in just two areas, would this equate to the same number of LSPs in IS-IS, and hence scale accordingly with IS-IS? 2) Is it possible for IS-IS to support the equivalent of an OSPF NSSA? In an OSPF NSSA, the area sees no external area routes, but ASBRs can be present in the area. In IS-IS, the ASBR equivalent would be a L1/L2 router. And it appears that all routers which perform L2 function must be interconnected, which means: * the ASBR (L1/L2 router) would see all of the AS routes. This breaks one aspect of an NSSA in that only routes within the areas are present (LSA type 1, 2 and 7) * in order to satisfy the L2 connectivity requirement, there would need to be a string of routers in the area which are L2 that connect the ASBR (L1/L2) back to the L2 backbone. This sort of defeats the concept of an area, which is isolated from the backbone as the backbone needs to be pulled into the area to the ASBR (L1/L2) 3) Why is it that by limiting the possible metric values to be between [0, 1023] allows SPF to be more efficient? Thanks Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=60217&t=60217 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
