A method for operating a communication device is disclosed. One embodiment includes the steps of: generating an intermediary key corresponding to peer to peer (P2P) communication between a client and a counterpart client; transmitting the intermediary key to the counterpart client; obtaining an intermediary path corresponding to the intermediary key; receiving the data through the intermediary path from the client that did not receive an acknowledgement for data transmitted to the counterpart client because of a change of a network address of the counterpart client; and transmitting the data to the counterpart client if the counterpart client accesses the changed network address by using the intermediary key.