Which statement is true about IS-IS hello (IIH) PDUs?

• A. The same IIH PDU is used for both point-to-point and broadcast networks.
• B. IIH PDUs maintain the link-state database synchronization.
• C. IIH PDUs provide the priority value used in DIS election.
• D. IIH PDUs are transmitted only at the beginning of adjacency establishment.

Answer: (C)

The statement about IS-IS Hello (IIH) PDUs that is true is that they provide the priority value used in the Designated Interim System (DIS) election. In IS-IS routing protocol, IIH PDUs play a crucial role in the neighbor discovery process and adjacency formation between routers. When routers send IIH PDUs, they include a priority value, which is essential for determining which router will become the DIS in a multi-access network. The DIS acts as a central point to manage the transmission of link-state information, and the router with the highest priority value is elected as the DIS. If two routers have the same priority, the router with the highest System ID will win the election.

Understanding the significance of IIH PDUs in the context of DIS election is key in IS-IS networking as it impacts how routers efficiently communicate and maintain their state information. This functionality underlines the need for effective neighbor discovery and compatibility in dynamic network environments.