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Overview

IS-IS is a dynamic routing protocol developed by the International Organization for Standardization (ISO) and commonly referred to as ISO 10589. IS-IS was originally developed at Digital Equipment Corporation for Phase V DECnet. The motivation to standardize IS-IS, however, was through the efforts of the American National Standards Institute (ANSI) X3S3.3 Network and Transport Layers Committee.

Similar to the Open Shortest Path First (OSPF) routing protocol, IS-IS is a link-state protocol. It builds a complete and consistent picture of a network’s topology by sharing link-state information across all network Intermediate System (IS) devices.

The IS-IS routing protocol provides routing for pure Open Systems Interconnection (OSI) environments. IS-IS as implemented on the E-series router supports IP networks and enables you to configure IS-IS as an IP routing protocol only. In IS-IS, networks are partitioned into routing domains, which are further divided into areas. A two-level hierarchical routing design is used. With this model, routing is referred to as level 1, level 2, or both level 1 and level 2.

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