Network Routing Issues: IS-IS on Broadcast Network

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The DIS Router sends CSNPs describing all the LSPs in the database every 3 seconds.

IS-IS (Intermediate System to Intermediate System) is a link-state routing protocol that operates in a broadcast network, such as Ethernet. IS-IS routers send Hello packets to establish adjacency and exchange link-state information.

In this scenario, Router A is sending Hello packets every three seconds, while Router B is sending Hello packets every nine seconds. Both routers are configured with the default IS-IS configuration values.

To determine the DIS (Designated Intermediate System) router in a broadcast network, all routers send Hello packets to the multicast MAC address 01:80:C2:00:00:14. The router with the highest priority becomes the DIS, and if there is a tie, the router with the highest MAC address becomes the DIS.

The two possible answers for this scenario are:

1. Router A is the DIS router and Router B is a non-DIS router. If Router A is sending Hello packets every three seconds, it is likely that it has the highest priority and became the DIS router. Router B, on the other hand, is sending Hello packets every nine seconds, which suggests that it is a non-DIS router.

2. Router B is the DIS router and Router A is a non-DIS router. If Router B is sending Hello packets every nine seconds, it is likely that it has a lower priority than Router A. However, if Router A is not sending Hello packets at the same time as Router B, it could mean that it is not detecting the Hello packets from Router B, which could be due to a network issue. In this case, it is possible that Router B is the DIS router and Router A is a non-DIS router.

Therefore, both options are possible, and without additional information, it is impossible to determine the correct answer.