Advanced Topics: NAT Traversal

Network address translation (NAT) was initially used to protect corporate networks from people attempting to access internal networks from the Internet. With one-to-one NAT, each computer accessing the Internet needs to have one public address. The network address and port translation (NAPT) technique makes it possible for multiple users to access the Internet without an application-level proxy, for all applications that use transport protocols that have a port information to characterize a connection in addition to the IP address. This chapter shows that NAT/NAPT problems should be avoided at all costs for large-scale deployments, as they can become maintenance and troubleshooting nightmare. The method has the advantage of cleanly separating the VoIP network and the regular data network, which helps delineate the respective responsibilities of the enterprise and the service provider in terms of security. Controlled Vocabulary Terms Internet telephony; network address translation; transport protocols; Voice over Internet protocol network