Which multicast address is designated for all routers using OSPF?

The multicast address designated for all routers using OSPF (Open Shortest Path First) is FF02::5. This address is part of the IPv6 multicast address space, specifically used for OSPFv3, which is the version of OSPF that supports IPv6.

When OSPF routers need to communicate updates about routing information, they send this information to the multicast address FF02::5. This ensures that all OSPF routers in the local network segment receive the routing information simultaneously. By using this multicast address, OSPF can efficiently manage routes without needing to send unicast messages to each individual router, which saves bandwidth and speeds up the routing process.

It's critical to note that other multicast addresses such as FF02::2, FF02::9, and FF02::A serve different purposes within IPv6 multicast operations and are not specifically designated for OSPF communications. FF02::2 is used for all IPv6 routers, FF02::9 is reserved for protocols like the Routing Information Protocol (RIP), and FF02::A is generally used for EIGRP (Enhanced Interior Gateway Routing Protocol). Thus, understanding the specific function of each address ensures proper network design and functionality.