Introduction to IS-IS
IS-IS is based on link-state technology, which has two levels of hierarchy. Networks can be divided into manageable-sized subdomains called areas. An area's topology information is held within that area. This containment of information is known as level 1. Level 2 connects multiple level 1 areas, which is how level 2 became known as the backbone area.
IS-IS forwards both OSI and IP packets unaltered; packets are transmitted directly over the underlying link-layer protocols without the need for mutual encapsulation. IS-IS uses the Dijkstra algorithm to find the shortest path to the destination.
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