IS-IS


Overview

  • Link-state, uses Dijkstra algorithm

Router Types

  • Level 1: intra-area (can only form relationships with other Level 1 routers).
  • Level 2: inter-area (can only form relationships with other Level 2 routers).
  • Level 1-2: both.

Routing

  • Level 1 ↔ Level 1
  • Level 2 ↔ Level 2
  • Level 1 ↔ Level 1-2 ↔ Level 2

Other Stuff

  • Area borders are between routers (i.e. on the link):
    • in contrast to OSPF where the area border is within an ABR.

Useful Articles

  • Digging deep into IS-IS.  [Network Collective]
  • RFC 8202: IS-IS multi-instance.  [Russ White]
  • IS-IS for IPv6.  [ipCisco]
    • Configuration example on Cisco IOS.  [ipCisco]
  • IS-IS configuration example on Cisco IOS.  [ipCisco]
  • Demystifying the IS-IS database.  [MellowD]
  • Junos day one: IS-IS for dummies.  [ipSpace]
  • Multi-level IS-IS in a single area?  Think again!  [ipSpace]
  • Multi-topology IS-IS.  [IOS Hints]
  • Basics of IS-IS.  [MPLS VPN]