Some of the timestamp protocols provide a means for the two nodes to synchronize their time when necessary. If a registration reply does not return promptly, the mobile node registers again with a new timestamp. In each registration the mobile node returns the latest nonce it has received. If the home agent sees the nonce it expects, the message is fresh. If a registration is rejected because its nonce is wrong, the mobile node simply registers again using the fresh nonce from the rejection message.
Attackers can break the simpler variants of both protocol families.
Attacks on a timestamp protocol usually try to make one of the nodes set its clock incorrectly. If the home agent's clock is set back to a previous time, it will accept replay of old registrations. If the mobile node's clock is set ahead, it will generate validated registrations that the attacker can replay in the future. Either of these attacks can be used to redirect traffic to an old location and to deny service. Attacks on a nonce protocol replay registration replies to make the mobile node use old nonces.