R1, R2, R3, and R4 run IS-IS, and the DIS priorities of their interfaces are...

DIS Election in IS-IS:

In IS-IS, theDesignated Intermediate System (DIS)is elected on broadcast networks to reduce the number of LSAs exchanged and maintain the LSDB.

The DIS is elected based onpriority:

The router with thehighest priorityis elected as the DIS.

If priorities are equal, theSystem IDis used as a tie-breaker, and the router with thehighest System IDbecomes the DIS.

HCIP-Datacom-Core Technology Training Material (IS-IS DIS Election Mechanism)​​.

Given DIS Priorities:

R1: Priority = 10

R2: Priority = 20

R3: Priority = 30

R4: Priority = 40

R4 has the highest DIS priority of 40, which makes it the clear choice for DIS election.

Scenario Details:

Since all devices are started simultaneously, the DIS election process will follow the priorities without requiring a tie-breaker (System ID).

Conclusion:

The device with the highest DIS priority isR4, and it will be elected as the DIS.