Chapter 6

OSPF and Integrated IS–IS

In protocol design, perfection has been reached not when there is nothing left to add, but when there is nothing left to take away.

Ross Callon (RFC1925)


In this chapter, we present two important link state routing protocols: Open Shortest Path First (OSPF) and Intermediate System-to-Intermediate System (IS–IS). They are interior gateway protocols (IGPs) used in an autonomous system (AS). They are often deployed by large Internet service providers within their networks. For each of these protocols, general operations and message structures are presented. Their differences are also highlighted.


OSPFv2; OSPFv3; LSA types; equal-cost multipath (ECMP); multitopology routing; integrated ...

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