OSPF- Loopback

R2

interface Loopback101
 ip address 102.1.0.1 255.255.255.0

router ospf 10

 network 102.1.0.1 0.0.0.0 area 0

R5

interface Loopback101

 ip address 201.2.0.1 255.255.255.0

 ip ospf network point-to-point

router ospf 10

network 201.2.0.1 0.0.0.0 area 0

R2#sh ip route | in 201.2

O     201.2.0.0/24 [110/2] via 25.0.0.5, 00:05:27, FastEthernet0/0

R2#sh ip ospf int lo101
Loopback101 is up, line protocol is up
  Internet Address 102.1.0.1/24, Area 0, Attached via Network Statement
  Process ID 10, Router ID 2.2.2.2, Network Type LOOPBACK, Cost: 1

R5#sh ip route | in 102

      102.0.0.0/32 is subnetted, 1 subnets

O        102.1.0.1 [110/2] via 25.0.0.2, 00:03:44, FastEthernet0/0

R5#sh ip ospf int lo101
Loopback101 is up, line protocol is up
  Internet Address 201.2.0.1/24, Area 0, Attached via Network Statement
  Process ID 10, Router ID 55.5.5.5, Network Type POINT_TO_POINT, Cost: 1
  Transmit Delay is 1 sec, State POINT_TO_POINT
  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

Now change network type on R2 also

interface Loopback101
 ip address 102.1.0.1 255.255.255.0
ip ospf network point-to-point

now in R5 , subnet with 24 bit is advertised

R5#sh ip route | in 102

      102.0.0.0/24 is subnetted, 1 subnets
O        102.1.0.0 [110/2] via 25.0.0.2, 00:00:03, FastEthernet0/0
R5#

R2#sh ip ospf int lo101
Loopback101 is up, line protocol is up
  Internet Address 102.1.0.1/24, Area 0, Attached via Network Statement
  Process ID 10, Router ID 2.2.2.2, Network Type POINT_TO_POINT, Cost: 1
  Topology-MTID    Cost    Disabled    Shutdown      Topology Name
        0           1         no          no            Base
  Transmit Delay is 1 sec, State POINT_TO_POINT