Category: IS-IS

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. In this post I will look at the following IS-IS configurations;

• Redistribution of OSPF into IS-IS, and the differences between L1 and L2.
• IS-IS Path selection when L1 and L2 routes are available.
• How and where to apply IS-IS Route Summarization.

IS-IS Lab Setup

Using Cisco’s Modeling Labs (CML) I build the following IS-IS and OSPF topology:

• 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 ) (R7, R8) running IOS with IOSv.
• 2 x L1L2 Router ( Center ) (R5, R6) running XRv with IOS-XR.
• 2 x L1 Router ( Center ) (R9, R10) running IOS with IOSv.
• 1 x OSPF Router (R11) running IOS with IOSv.

Logical View:

Physical View:

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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

Using Cisco’s Modeling Labs (CML) I build the following IS-IS topology:

• 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:

(more…)