OSPF area authentication

 interface Serial1
   ip address 131.108.1.3 255.255.255.0
   ip ospf message-digest-key 1 md5 abcdef
 !
 router ospf 10
   area 0 authentication message-digest
   network 131.108.0.0 0.0.255.255 area 0

• The MD5 key, must be done on both sides of link.
• If you set the authentication for the whole area, then it should be done on all routers in the area.