US Patent 7536552 Upper-level protocol authentication

A method for authenticating communication traffic includes receiving a first message, sent over a network from a source address, requesting information from a server in accordance with a higher-level protocol. A challenge is sent to the source address in reply to the first message, in accordance with the higher-level protocol. A second message is received from the source address following the challenge, and the legitimacy of the source address is assessed by determining whether the second message contains a correct response to the challenge.