 This problem can be mitigated by tracking the destination IP address in addition to the port (thus sharing a single local port with many remote hosts), at the expense of implementation complexity and CPU/memory resources of the translation device.Because the internal addresses are all disguised behind one publicly accessible address, it is impossible for external hosts to initiate a connection to a particular internal host without special configuration on the firewall to forward connections to a particular port.Applications such as VOIP, videoconferencing, and other peer-to-peer applications must use NAT traversal techniques to function.