When neighbor authentication has been configured on a router, the router authenticates the source of each routing update packet that it receives. This is accomplished by the exchange of an authenticating key (sometimes referred to as a password) that is known to both the sending and the receiving router.

To exchange routing update information in a secure manner, enable OSPF authentication. OSPF authentication can either be none (or null), simple, or Message Digest 5 (MD5).

OSPF supports 3 types of authentication:

Click the Play button in the animation to see how MD5 authentication is used to authenticate neighboring peer messages.

Note: RIPv2, EIGRP, OSPF, IS-IS, and BGP all support various forms of MD5 authentication.