A network address translation apparatus and method within a Voice over Internet Protocol (VoIP) router is described. This apparatus and method operates within networking devices such as routers, switches, bridges, etc. These devices masks both source and destination addresses and may either replace or complement a firewall in providing security. According to one embodiment, network type information, corresponding to the gateways within connection, is embedded in a port number within a packet header. This network type information is extracted and analyzed to identify the network types of both gateways within the connection. According to another embodiment, a port number is assigned according to the network types of both gateways within a connection. Thus, this network type information may be identified by processing the port number on which a packet is received.