What is the multicast address used for all OSPF routers?

The correct multicast address used for all OSPF (Open Shortest Path First) routers is 224.0.0.5. This specific address is defined in the Internet Assigned Numbers Authority (IANA) special-use address ranges, and it is designated for use by all OSPF routers within a network.

When OSPF routers send updates or other protocol messages, they use this multicast address to ensure that all OSPF-enabled devices on the shared link can receive the information at the same time, facilitating efficient communication and network updates among routers. As a result, this address plays a crucial role in maintaining OSPF operation by enabling all participating routers to effectively receive routing updates and other important network information.

In contrast, the other addresses listed have different usages within multicast addressing and do not pertain to OSPF:

• 224.0.0.6 is specifically used for OSPF designated routers.

• 225.0.0.5 and 239.0.0.5 are not standard addresses associated with OSPF and do not serve the same purpose within OSPF routing protocols. Thus, using 224.0.0.5 is essential for OSPF routers to communicate effectively in