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Intermediate System to Intermediate System (IS-IS)

The Intermediate System to Intermediate System (IS-IS) routing protocol is a link-state interior gateway protocol (IGP) similar to OSPF. IS-IS operates at layer 2 (L2), unlike OSPF and BGP which operate at layer 3 (L3). IS-IS automatically locates neighbors on directly connected L2 networks and neighbors cannot be configured manually. IS-IS can route both IPv4 and IPv6 traffic with the same configuration, unlike OSPF which requires configuring OSPFv2 and OSPFv3 separately.

See also

• IS-IS and OSPF Comparison

• IS-IS Router Using Ethernet or TEB GRE Interfaces

• FRR IS-IS Documentation

Warning

Due to the fact that IS-IS operates at L2, active IS-IS interfaces must be able to carry L2 information. Currently this is limited to Ethernet interfaces as well as GRE interfaces in Transparent Ethernet Bridging (TEB) mode.

IS-IS Topics

• IS-IS Terminology
  • IS-IS PDU Types
  • Levels
  • Network Entity Title (NET)
• IS-IS Required Information
• IS-IS Example
• IS-IS Configuration
  • Enable IS-IS
  • IS-IS Server Configuration
  • IS-IS Interface Configuration
  • IS-IS Debugging Information
• IS-IS Status
  • Configuration Information
  • Status Information

See also

For additional detail on IS-IS routing, read the following in order:

• ISO/IEC 10589

• RFC 1142

• RFC 1195