Question

A network engineer configures a Loopback0 interface with IP address 10.10.10.1/24 on router R3 and enables OSPF on it using 'network 10.10.10.0 0.0.0.255 area 0'. On neighboring router R1, the route to R3's loopback appears in the routing table as '10.10.10.1/32' instead of the expected '10.10.10.0/24'. The engineer needs R1 to learn the full /24 prefix. What is the cause and the correct remediation?

Accepted Answer

By default OSPF advertises loopback interfaces as /32 host routes; configure 'ip ospf network point-to-point' on Loopback0 to advertise the configured subnet mask.

Answer

The loopback is in a different area; move it to area 0 with 'network 10.10.10.0 0.0.0.255 area 0' to advertise the /24.

Answer

OSPF auto-summarization is enabled; disable it with 'no auto-summary' under the OSPF process to advertise the /24 prefix.

Answer

The mask is being overridden by a route map; remove the 'set ip address' statement to restore the /24 advertisement.