IS-IS Area Configuration in Junos OS

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To enable IS-IS on a Junos device, one of the parameters you must configure is the network entity title (NET), which is usually set on the lo0 interface. The NET contains the area ID, system ID, and selector.

The correct answer is C. [edit protocols isis level 1].

Intermediate System-to-Intermediate System (IS-IS) is a routing protocol that operates at the OSI layer 2 level and is used to distribute routing information among routers in a network. It uses a hierarchical structure, where routers are grouped into areas. Each area has a unique area ID, and all routers within an area must have the same area ID.

To configure the area value for IS-IS in Junos OS, you need to edit the IS-IS protocol configuration under the [edit protocols isis] hierarchy. The specific configuration statement for setting the area value depends on the level of the IS-IS instance:

• For level 1 IS-IS, you can set the area ID under the [edit protocols isis level 1] hierarchy. You can use the following configuration statement to set the area ID:

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set protocols isis level 1 area <area-id> 

• For level 2 IS-IS, you can set the area ID under the [edit protocols isis level 2] hierarchy. You can use the following configuration statement to set the area ID:

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set protocols isis level 2 area <area-id> 

Note that if you are configuring IS-IS on a loopback interface, you can set the area value under the [edit interfaces lo0 unit 0 family iso address] hierarchy using the following configuration statement:

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set interfaces lo0 unit 0 family iso address <area-id>.00 

However, this configuration only applies to the router's own IS-IS process and does not affect the IS-IS process of other routers in the network.

Therefore, the correct answer is C. [edit protocols isis level 1] for configuring the area value for IS-IS in Junos OS.