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How to configure IS-IS for IP

Core Issue

Integrated Intermediate System-to-Intermediate System (IS-IS) is a link-state routing protocol that has evolved from International Organization for Standardization (ISO) IS-IS. While ISO IS-IS was an Open System Interconnection (OSI) protocol meant for supporting only ISO Connectionless Network Service (CLNS) networks, Integrated IS-IS can support CLNS only, IP-only, or dual (both CLNS and IP) environments. IS-IS runs directly on top of the data link layer without being encapsulated into any Layer 3 protocol.


A router configured for IS-IS (either ISO or Integrated) requires a Network Entity Title (NET) address to uniquely identify itself in the network, just like the Open Shortest Path First (OSPF) router ID in IP networks. This is true even if Integrated IS-IS is being used in an IP-only environment. To configure a router for IS-IS in IP networks, perform these steps:

  1. Issue the router isis command from global configuration mode.

  2. Assign the NET address by issuing the net command from configuration router mode.

  3. Issue the ip router isis command under the interfaces that need to be included under IS-IS.

Other commands might be needed for fine tuning and optimization, depending on the requirements.

For more information, refer to these documents: