NAT


NAT (Network Address Translation) is a technique which could modify the private address to legal IP address. It is not only perfectly solve the lack of IP address, but also prevent the attack from outside. It could hide and protect those systems which are inside the WAN.

There are four types of NAT:

1. Full cone NAT:
          It is also know as one_to_one NAT.

         

          Once an internal address (iAddr:iPort) is mapped to an external address (eAddr:ePort), any packets from iAddr:iPort will be sent through eAddr:ePort. Any external host can send packets to iAddr:iPort by sending packets to eAddr:ePort.

2. Restricted Cone Nat:

         

          Once an internal address (iAddr:iPort) is mapped to an external address (eAddr:ePort), any packets from iAddr:iPort will be sent through eAddr:ePort. An external host (hAddr:any) can send packets to iAddr:iPort by sending packets to eAddr:ePort only if iAddr:iPort has previously sent a packet to hAddr:any. "Any" means the port number doesn't matter.

3. Port Restricted Cone Nat:
         no Like an address restricted cone NAT, but the restriction includes port numbers.
         

          Once an internal address (iAddr:iPort) is mapped to an external address (eAddr:ePort), any packets from iAddr:iPort will be sent through eAddr:ePort. An external host (hAddr:hPort) can send packets to iAddr:iPort by sending packets to eAddr:ePort only if iAddr:iPort has previously sent a packet to hAddr:hPort.

4. Symmetric NAT:
         no user has any particular rights or delegation and each and every decision
         (including on the acceptance of each candidate to be a constituent) is always taken directly
         by the whole constituency by vote. In this case, even when they see the same data, constituents
         may draw different conclusions as to the composition of the constituency.
         

          Each request from the same internal IP address and port to a specific destination IP address and port is mapped to a unique external source IP address and port, if the same internal host sends a packet even with the same source address and port but to a different destination, a different mapping is used. Only an external host that receives a packet from an internal host can send a packet back.

To enable the use of DDP2P, some systems might be behind the NAT, it would prevent the communication between each peers. So, we provide serval methods to pirece the NATs.





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