 NAT "port preservation" for outgoing TCP connections is crucial for TCP NAT traversal, because as TCP requires that one port can only be used for one communication at a time, programs bind distinct TCP sockets to ephemeral ports for each TCP communication, rendering NAT port prediction impossible for TCP.On the other hand, for UDP, NATs do not need to have "port preservation".Indeed, multiple UDP communications (each with a distinct endpoint) can occur on the same source port, and applications usually reuse the same UDP socket to send packets to distinct hosts.