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

  • Running IS-IS over unnumbered Ethernet interfaces. [ipSpace]

  • IS-IS flooding details. [ipSpace]

  • LSA/LSP flooding in OSPF and IS-IS. [ipSpace]

  • 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]

© Robert Larsen. All rights reserved.