NAT Learning Notes

NAT Introduction

NAT, full name network address translation (translation), is a technology that overrides the source IP address or destination IP address when IP packets pass through a router or firewall .

The classification and introduction of NAT

The most important thing in a NAT device is the mapping table, the MAP table structure:

which

External protocol: The IP address assigned to the device by the external network of the NAT device

External port: The port number that the NAT device allocates for this connection from the ports pool of the device

Internal address: NAT device Internal network device such as PC, smart phone LAN IP address

Internal Port: The port number used by a device in the NAT device's internal network to issue a network message

Destination Address: The IP address of the device that you want to receive messages from

Destination port: The port number of the device that you want to receive the message to

The main role of NAT

When an internal message is sent to an external device through a NAT device, the NAT device changes the source IP address in the message and the source port to the NAT device's own IP address and port number, and logs the mapping operation to the mapping table, which allows the destination device to assume that the message was sent by the NAT device

When the target device replies to a NAT device, Nat looks for a matching record in the mapping table, discards the message if no match is reached, changes the destination address and destination port number of the message to the internal address and internal Port number in the mapping table, and sends the message to the internal device

This completes the request and reply message communication work, the NAT device in this process acts as a network masking or IP masking, so that the external device does not know the existence of internal devices, can only communicate directly with the NAT device, All communication needs to be handled by a NAT device.

Reference information:

http://cgs1999.iteye.com/blog/1994072

Https://zh.wikipedia.org/wiki/%E7%BD%91%E7%BB%9C%E5%9C%B0%E5%9D%80%E8%BD%AC%E6%8D%A2

Http://www.h3c.com.cn/Service/Channel_Service/Operational_Service/ICG_Technology/201001/662399_30005_0.htm

Http://www.h3c.com.cn/MiniSite/Technology_Circle/Net_Reptile/The_Five/Home/Catalog/201206/747042_97665_0.htm

NAT Learning Notes