! Two isolated IOS-style routers. Adapt interface names before use.
! Documentation networks; no connection to an employer network.
! ROUTER A
hostname LAB-R1
interface GigabitEthernet0/0
 ip address 198.51.100.1 255.255.255.252
 no shutdown
interface Loopback0
 ip address 192.0.2.1 255.255.255.255
router ospf 10
 router-id 1.1.1.1
 passive-interface default
 no passive-interface GigabitEthernet0/0
 network 198.51.100.0 0.0.0.3 area 0
 network 192.0.2.1 0.0.0.0 area 0
!
! ROUTER B - apply this section only on the second router
hostname LAB-R2
interface GigabitEthernet0/0
 ip address 198.51.100.2 255.255.255.252
 no shutdown
interface Loopback0
 ip address 203.0.113.1 255.255.255.255
router ospf 10
 router-id 2.2.2.2
 passive-interface default
 no passive-interface GigabitEthernet0/0
 network 198.51.100.0 0.0.0.3 area 0
 network 203.0.113.1 0.0.0.0 area 0
!
! VERIFY on each router:
! show ip ospf neighbor
! show ip route ospf
! show ip ospf interface GigabitEthernet0/0
! Single uplink: link failure interrupts this topology. No failover is claimed.