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IS-IS
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based on work done at Digital for DECnet Phase V
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originally developed for CLNP (Connection-Less Network Protocol), then extended to IP (Integrated IS-IS)
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ISO 10589 - specification of IS-IS
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link-state hierarchical routing protocol
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IS-IS packets have complex structure (hello packets, link-state packets, sequence number packets)
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link-state update messages - ISs learn the network topology
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IS-IS distinguishes between Level 1 and Level 2 ISs
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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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