Networking / Beginners

Integrated Intermediate System-to-Intermediate System

IS-IS is an OSI link-state hierarchical routing protocol that is based on work originally done at Digital Equipment Corporation for DECnet/OSI (DECnet Phase V). This protocol floods the network with link-state information to build a complete, consistent picture of network topology.

The International Organization for Standardization (ISO) has developed the following routing protocols for use in the Open System Interconnection (OSI) protocol suite:

  • Intermediate System-to-Intermediate System (IS-IS) protocol
  • End System-to-Intermediate System (ES-IS) protocol
  • Interdomain routing protocol (IDRP)

The American National Standards Institute (ANSI) X3S3.3 (network and transport layers) committee was the motivating force behind ISO standardization of IS-IS, which was originally developed to route in ISO connectionless network protocol (CLNP) networks. A version has since been created that supports both CLNP and IP networks. It is usually referred to as integrated IS-IS; this is the version discussed here.

OSI routing protocols are summarized in several ISO documents; those dealing with IS-IS are as follows:

  • ISO 10589: Standards definition for IS-IS
  • RFC 1195: Intermediate IS-IS
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