The concept (a) NAT and works
Simply put, nat is a private URL into the URL of a total technology. NAT is typically deployed at the network egress position an organization to become NAT gateway. For chestnuts, some wanted to leave private messages, you must go through NAT gateways transmit data to the public Internet, achieved by nat source IP address mapping for public IP addresses, Internet IP is actually found that the private IP, it will be requested service implementation, and back to the source IP through the gateway. Such a host to a private network requests and responses to the public network server is realized.
Note: Network access can only be initiated first by the private network side, the public is unable to take the initiative to access the private network host.
Category (b) NAT's
1. Static NAT: one mode, namely an internal host occupies a unique public IP, commonly used server.
2. Dynamic NAT: one mode, the upcoming unregistered IP addresses are mapped to an address registered IP address pool.
3. NAPT: Many-mode, is about to multiple private IP public IP mapped to a different port number, the main principle is the uniqueness of the port number. Note: the port number of the transport layer is greater than 1024.
(C) NAT implementation
1. To achieve a static NAT is divided into three steps (the code is implemented ip and port number are based on the figure):
Verify: L1-V3ping external network through L4
Explanation: show ip nat translations by command, it can be seen within the IP network server with public IP conversion.
2.NAPT implementation is divided into five steps :
The above is my understanding and realization of NAT, if insufficient, looking bear.
References:
Cisco simulator video to explain the realization of nat