What protocol does OSPF use for multicast communications?

OSPF, or Open Shortest Path First, utilizes a specific multicast address for sending routing protocols' information packets between routers. The protocol designated for OSPF communications is identified by IP protocol number 89. This unique designation allows routers to recognize and process OSPF messages effectively, differentiating them from other types of network communications.

Multicast communications in OSPF specifically leverage the multicast addresses 224.0.0.5 and 224.0.0.6. These addresses enable OSPF routers to send updates and routing information efficiently within an OSPF area, ensuring that only OSPF routers receive the updates intended for them.

Using IP protocol number 89 is essential because it is specifically defined for OSPF, providing the necessary framework for the protocol to operate within the broader Internet Protocol suite. Other protocols like TCP and UDP, which are associated with IP protocols 6 and 17 respectively, are not used by OSPF for these purposes, emphasizing the unique nature of OSPF’s requirements for routing communications.