Router Priorities in IS-IS Network

C

IS-IS (Intermediate System to Intermediate System) is a routing protocol used in larger service provider networks and can also be used in enterprise networks. In an IS-IS network, the designated intermediate system (DIS) is responsible for flooding link-state information throughout the network.

When a new router is added to an IS-IS network, it can potentially become the new DIS, depending on its priority value. The priority value is a configurable parameter on each IS-IS router, and the router with the highest priority value becomes the DIS.

In this scenario, Router A is the current DIS with a priority of 64, and Router B comes online with a priority of 100. Based on this information, we can conclude that Router B has a higher priority value than Router A and can potentially become the new DIS.

Now let's look at each of the answer options:

A. Router A remains as the DIS. This option is not correct because Router B has a higher priority value than Router A, which means that Router B can potentially become the new DIS.

B. Router A remains the DIS and Router B becomes the backup DIS. This option is also not correct because if Router B becomes the new DIS, Router A will no longer be the DIS. Additionally, IS-IS does not have a backup DIS concept.

C. Router B becomes the DIS. This option is correct based on the information given. Router B has a higher priority value than Router A, which means that Router B can potentially become the new DIS.

D. Router B becomes the DIS and Router A becomes the backup DIS. This option is not correct because IS-IS does not have a backup DIS concept.

Therefore, the correct answer is C. Router B becomes the DIS.