Firewall traversal is an interesting dilemma . While firewall traversal may sound like it refers to the act of someone hacking across your firewall, it is far less scary than it sounds. It simply refers to the connection made when cross NAT gateways, which is technical jargon that describes how your network allows many computers to share a single connection. It happens in almost every network model, even the little cheap firewall/router devices that are used in home wireless devices. Each computer that wants to access the internet must have a unique identification, known as an IP address. Public addresses that are unique from the perspective of the outside world are limited, so giving each computer its own IP address is not feasible. A router splits a bunch of private addresses across a single public address. Firewall traversal becomes an issue when an application that runs on a workstation requires a public address to allow communcation back to the device. As an example, if your laptop runs a file sharing application that acts as a server, someone outside your network will not be able to talk to your machine specifically, only your firewall and its IP address. That is where firewall traversal comes in. Firewall traversal technologies allow visibility of your computer back through your firewall when you initiate this kind of connection. Firewall traversal has become more of an issue with the advent of voice over IP; IP based phones establish peer to peer connections with other phones, and the data packets must use firewall traversal to find their way back to your phone when you make a call. If you plan to deploy an IP phone system in your company, firewall traversal methods should be looked into to make sure that your existing equipment will be able to handle the firewall traversal technologies involved.
