The Complete IS-IS Routing Protocol

IS-IS has always been my favourite Interior Gateway Protocol. Its elegant simplicity, its well-structured data formats, its ?exibility and easy extensibility are all appealing – IS-IS epitomizes link-state routing. Whether for this reason or others, IS-IS is the IGP of choice in some of the world’s largest networks. Thus, if one is at all interested in routing, it is well worth the time and effort to learn IS-IS. However, it is hazardous to call any routing protocol “simple”. Every design decisi