Cisco Certified Network Associate (CCNA) Practice Exam

Which multicast address is used by OSPF to send hello packets?

1. 224.0.0.6

2. 239.255.255.255

3. 224.0.0.5

4. 225.0.0.5

The correct answer is: 224.0.0.5

The correct multicast address used by OSPF to send hello packets is 224.0.0.5. This address is designated for OSPF routers to communicate with all OSPF-enabled devices on the same local network segment. When OSPF routers send hello packets, they utilize this multicast address to ensure that all OSPF devices on that segment receive the packets simultaneously. Using a multicast address like 224.0.0.5 allows OSPF to facilitate efficient communication, as it avoids broadcasting to all devices, which can create unnecessary traffic. Instead, it specifically targets OSPF routers, making the process of establishing adjacency and exchanging routing information more efficient and streamlined. The other addresses mentioned are associated with different protocols or functions. For instance, 224.0.0.6 is used for OSPF DR (Designated Router) processes, whereas 239.255.255.255 is a local multicast address typically for applications and not specific to OSPF. 225.0.0.5 is not a valid multicast address used in standard networking protocols.