Abstract: The present invention supports an authentication protocol on a foreign agent to avoid rejecting re-registration request when congestion has delayed receipt at a mobile node of a foreign agent challenge code in a registration reply or agent advertisement message. Upon receipt of a re-registration request message containing a stale foreign agent challenge code, the identification code of the re-registration request message is compared to the identification code of the previous valid registration request message. If the identification code is greater than and not equal to the identification code in the previous valid request message, the foreign agent authenticates the message. The authenticated registration request message is processed to reset the lifetime so the communication session can continue.