[轉］STUN protocol

fr3@k 大大的一系列介紹，還沒空消化
先轉載一下
http://fsfoundry.org/codefreak/2006/09/20/nat-traversal-part-0/
http://fsfoundry.org/codefreak/2006/09/21/nat-traversal-part-1-nat-behavior/
http://fsfoundry.org/codefreak/2006/10/01/nat-traversal-part-2-stun/
http://fsfoundry.org/codefreak/2007/04/14/nat-traversal-part-3-turn/