Four NAT network structures

introduction

NAT is an address translation method that converts internal network address mapping to external network address, which saves limited IP address resources. Generally speaking, it is divided into symmetrical NAT and conical NAT. The conical NAT is divided into complete cone NAT, IP restricted cone NAT, and Port restricted cone NAT.

1 Completely conical NAT

Full-cone NAT means that the same internal network IP1+Port1 sends data to any external network, and the NAT will be mapped to the same external network IP2+Port2; and when the external network sends data to IP2+Port2, it will also be converted To the internal network IP1+Port1. The proxy node of some reverse proxy servers is this type of NAT.

2 IP restriction cone NAT

IP restriction cone NAT refers to the same internal network IP1+Port1 sending data to any external network, and it will be mapped to the same external network IP2+Port2 in the NAT; but this address mapping is associated with the external network destination host IP That is to say, when the internal network IP1+Port1 does not actively send data to the external network host of IP3, then the host of IP3 sends data to IP2+Port2, which will be discarded by NAT.

3 Port restriction cone NAT

Port restricted cone NAT means that the same internal network IP1+Port1 sends data to any external network, and it will be mapped to the same external network IP2+Port2 in the NAT; but this address mapping is with the external network destination host IP and port Associated, that is, when the internal network IP1+Port1 does not actively send data to Port3 of the external network host of IP3, then IP3+Port3 sends data to IP2+Port2, which will be discarded by NAT. The IP restricted cone NAT only recognizes the last name and does not ask the first name, while the Port limit cone NAT recognizes both the last name and the first name.

4 Symmetric NAT

Symmetric NAT means that when the internal network IP1+Port1 sends data to the external network IP2+Port2, the NAT will be mapped to an external network IP3+Port3; when the external network IP4+Port4 sends data, the NAT will be mapped to IP5+Port5 of an external network. This mechanism cannot guarantee the consistency of the mapped external network IP and port when the same internal network IP and port send data to different external network IPs and ports.

5 Summary

P2P hole punching technology can be established for the three cone NATs, but the P2P effect cannot be achieved for symmetric networks.