ISIS Configuration Example on Cisco IOS

isis-topology-ipcisco-2

In this Cisco ISIS configuration example, we will configure an ISIS domain and see how to establish ISIS Routing.

For our example we will use the below four-routered topology. Here, we will have 3 different area. We are using multi area model to show you the link level configurations.

isis-topology-ipcisco

Let’s start the ISIS configuration.

Firstly we will create the router ISIS process with the value “1” and we will give a “net” address to each router. After that we will set the router type. By default all routers are Level 1/2 .
By the way, let’s remember ISIS router types quickly;

L1 routers, establish neighbourship with only the routers in the same area.
L2 routers, establish neighbourship with routers in different areas or in the same area.
L1/2 routers, establish neighbourship with routers in any area.

How about LSDBs?

• L1 routers have Level-1 LSDB for the area
• L2 router s have Level-2 LSD for inter-area (between areas)
• L1 routers has two separate LSDB for both Level-1 and Level-2

 
Router A # config terminal
Router A (config) # router isis 1
Router A (config-rtr)# net 49.0000.0000.0000.AAAA.00
Router A (config-rtr)# is-type level-2-only
 
Router B # config terminal
Router B (config) # router isis 1
Router B (config-rtr)# net 50.0000.0000.0000.BBBB.00
Router B (config-rtr)# is-type level-2-only
 
Router C # config terminal
Router C (config) # router isis 1
Router C (config-rtr)# net 51.0000.0000.0000.CCCC.00
Router C (config-rtr)# is-type level-1-2
 
Router D # config terminal
Router D (config) # router isis 1
Router D (config-rtr)# net 51.0000.0000.0000.DDDD.00
Router D (config-rtr)# is-type level-1-2

isis-topology-with-levels

The other articles on IS-IS Protocol are below:

Routing With IS-IS Protocol – Part 1
Routing With IS-IS Protocol – Part 2 (IS-IS Addresses)
Routing With IS-IS Protocol – Part 3 (IS-IS Packet Types)
Routing With IS-IS Protocol – Part 4 (IS-IS Adjacency)
Routing With IS-IS Protocol – Part 5 (IS-IS versus OSPF)

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