title: How to understand the Kademlia(KAD) protocol
body: <p>Recently, I've read a document of the Kademlia Protocol, I tried to understand the protocol, but I still have some question:
  Why a node must find another node when he knows its ID but ip or port?
  Why he has the ID while he doesn't know the ip or port, where did he get the ID?
  I think the "distance" between two different nodes is not a routing distance or real distance, it's only a virtual distance that can be used the algorithm to find the node quickly, it's that right?</p>
  
  <p>Maybe my English is not very clear because English is not my mother tongue, but I'll try to express myself clear if you need.
  Thanks very much!</p>