How IS-IS Works
IS-IS is a link-state protocol that runs the shortest path first (SPF or Dijsktra) algorithm to calculate the best path through a network. IS-IS provides two levels of routing for hierarchy—level 1 (L1) routing areas are interconnected using level 2 (L2) routing. The L2 routing domain is sometimes called the core.
IS-IS uses hierarchical addressing to break an autonomous system up into L1 routing areas and to distinguish between L1 and L2 routes. All nodes within a given area use L1 routing to reach each other, whereas nodes in different areas must use L2 routing to reach one another.
As a link-state protocol, IS-IS relies on routers flooding the state of their links to all other routers within their area (L1 or L2) to propagate ...
Get Advanced IP Network Design (CCIE Professional Development) now with the O’Reilly learning platform.
O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.
