OSI Routing Protocol (3)

IS-IS

• based on work done at Digital for DECnet Phase V

• originally developed for CLNP (Connection-Less Network Protocol), then extended to IP (Integrated IS-IS)

• ISO 10589 - specification of IS-IS

• link-state hierarchical routing protocol

• IS-IS packets have complex structure (hello packets, link-state packets, sequence number packets)

• link-state update messages - ISs learn the network topology

• IS-IS distinguishes between Level 1 and Level 2 ISs

• default single metric assigned by an administrator (max path value 1024); optional metrics: delay, expense and error; IS-IS uses these metrics to compute routes through the network.

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