Intermediate System to Intermediate System (IS-IS)

Intermediate System to Intermediate System (IS-IS) is a dynamic link-state routing protocol widely used in large-scale networks, especially in service provider environments. One of its features is interlevel routing, which allows communication between IS-IS levels (Level 1 and Level 2). This post explains IS-IS interlevel routing and provides configuration examples to implement it in practical scenarios.

IS-IS Lab Setup

 

Labs download

The CML Lab is available for download here.

1 – Lab IS-IS Configuration

Using Cisco’s Modeling Labs (CML) I build the following MPLS-SR lab using OSPF as the IGP.

  • 2 x L2 Router ( Top )  (R1, R2) running XRv with IOS-XR.
  • 2 x L1L2 Router ( left ) (R3, R4) running XRv with IOS-XR.
  • 2 x L1 Router ( left ) (R9, R10) running IOS with IOSv.
  • 2 x L1L2 Router ( Center ) (R5, R6) running XRv with IOS-XR.
  • 2 x L1 Router ( Center ) (R11, R12) running IOS with IOSv.
  • 2 x L1L2 Router ( Right ) (R7, R8) running XRv with IOS-XR.
  • 2 x L1 Router ( Right ) (R13, R14) running IOS with IOSv.

Logical View:

Physical View:

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