configure terminal
hostname R2
interface loopback 2
description Marketing Department
ip address 10.1.2.1 255.255.255.0
interface serial 0/0/0
ip address 10.1.12.2 255.255.255.0
no shutdown
interface serial 0/0/1
ip address 10.1.23.2 255.255.255.0
clockrate 64000
no shutdown

router ospf 1
network 10.1.12.0 0.0.0.255 area 0
network 10.1.2.0 0.0.0.255 area 0
exit
interface loopback 2
ip ospf network point-to-point

router ospf 1
network 10.1.23.0 0.0.0.255 area 23

router ospf 1
area 23 virtual-link 192.168.103.

interface serial0/0/0
ip ospf authentication message-digest
ip ospf message-digest-key 1 md5 cisco