In this lab we will configure the Open Shortest Path First routing protocol (OSPF) between two routers in the same area. With OSPF you must use a wildcard mask in your network statements as shown below.
CIDR Information
Address: 172.16.0.1 10101100.00010000.00000000.000000 01 Netmask: 255.255.255.252 = 30 11111111.11111111.11111111.111111 00 Wildcard: 0.0.0.3 00000000.00000000.00000000.000000 11 ! Network: 172.16.0.0/30 10101100.00010000.00000000.000000 00 HostMin: 172.16.0.1 10101100.00010000.00000000.000000 01 HostMax: 172.16.0.2 10101100.00010000.00000000.000000 10 Broadcast: 172.16.0.3 10101100.00010000.00000000.000000 11 Hosts/Net: 2 Class B, Private Internet
OSPF Configuration
R1(config)#router ospf 1 ! R1(config-router)#network 172.16.0.0 ? A.B.C.D OSPF wild card bits ! R1(config-router)#network 172.16.0.0 0.0.0.3 area ? <0-4294967295> OSPF area ID as a decimal value A.B.C.D OSPF area ID in IP address format ! R1(config-router)#network 172.16.0.0 0.0.0.3 area 0 ! R2(config)#router ospf 1 R2(config-router)#network 172.16.0.0 0.0.0.3 area 0
Verification
R1# *Oct 16 05:24:08.650: %OSPF-5-ADJCHG: Process 1, Nbr 172.16.0.2 on GigabitEthernet0/0 from LOADING to FULL, Loading Done ! R2# *Oct 16 05:24:08.922: %OSPF-5-ADJCHG: Process 1, Nbr 172.16.0.1 on GigabitEthernet0/0 from LOADING to FULL, Loading Done ! R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 172.16.0.2 1 FULL/DR 00:00:35 172.16.0.2 GigabitEthernet0/0 ! R2#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 172.16.0.1 1 FULL/BDR 00:00:34 172.16.0.1 GigabitEthernet0/0
From the output above we can see that R2 is the Designated Router (DR) and R1 is the Backup Designated Router (BDR). The election of R2 as the DR was made because it has the highest Neighbor ID.
OSPF Hello Packet in Wireshark captured from R1
