NAT traversal (NAT-T) is a feature that allows IPsec traffic to “traverse” through NAT or PAT points without the incompatibilities that would normally arise. NAT (or PAT) works by translating a local address or addresses to a public address or several public addresses. In the case of PAT, several local addresses are translated to one global address using different ports. This means that, for local traffic [source IP address/port and destination IP address/port], PAT will change the source IP address to the global PAT IP address and will also change the source port to a unique port.