Million common configuration is here.

1. Cisco Virtual Lab Convenient startup-config
2. Router: Cisco Equipment Convenient startup-config ($2) · Snippets · GitLab

• R1

configure terminal
!
interface GigabitEthernet 0/1
 ip address 10.1.2.1 255.255.255.0
 no shutdown
interface Loopback 0
 ip address 1.1.1.1 255.255.255.255
 no shutdown
!
router ospf 1
 network 10.1.2.1 0.0.0.0 area 0
 network 1.1.1.1 0.0.0.0 area 0
exit
!
end

• R2

configure terminal
!
interface GigabitEthernet 0/1
 ip address 10.1.2.2 255.255.255.0
 no shutdown
interface Loopback 0
 ip address 2.2.2.2 255.255.255.255
 no shutdown
!
router ospf 1
 network 10.1.2.2 0.0.0.0 area 0
 network 2.2.2.2 0.0.0.0 area 0
exit
!
end