Summary
This chapter reviews the basic concepts underlying the design of the IS-IS routing protocol. The chapter also discusses the two-level hierarchy for controlling distribution of routing information within IS-IS areas and between them: Level 1 and Level 2, respectively. You learned that technically all IS-IS routers belong to one physical Level 1 area because of the node-based addressing scheme of CLNP. The related issue of suboptimal interarea routing resulting from the architecture proposed in ISO 10589 and adopted by RFC 1195 is discussed in detail in Chapter 7, “General Network Design Issues.” Chapter 7 also discusses workarounds and IS-IS protocol enhancements that address this major limitation of the original IS-IS protocol architecture. ...
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