NAT Traversal

March 2008 document describing nat traversal approaches for TCP/UDP based applications: State of Peer-to-Peer (P2P) Communication across Network Address Translators (NATs)

terminology:

• endpoint mapping
  • endpoint independent
  • endpoint dependent: address dependent & address-port dependent

• endpoint filtering
  • endpoint independent
  • endpoint dependent: address dependent & address-port dependent

   A NAT device employing "Endpoint-Dependent Filtering" will accept
   incoming traffic to a mapped public port from only a restricted set
   of external endpoints on the public network.

3.1 relaying

make the peer-to-peer communication look to the network like client/server: the two clients (behind NAT) can simply
use the server S to relay messages between them.