
Impact of Network Address Translation 127
NAT Traversal UDP Tunneling
To solve the problems that occur when the tunnel needs to terminate behind NAT and NAPT
gateways, the Internet Engineering Task Force (IETF) Mobile IP working group standardized
RFC 3519, which defines a UDP tunneling protocol to be used for both the forward and reverse
Mobile IP tunnels. The new protocol defines extensions to the registration and agent
advertisement portions of the Mobile IP protocol. A key feature of this NAT–Mobile IP solution
is that data packets are now also sent to the UDP ports that set up the Mobile IP registration,
that is, UDP port 434 on the Home