Shulou(Shulou.com)06/01 Report--

1. Network address translation NAT:

Some hosts in the private network have been assigned local IP addresses, but now the easiest way to communicate with the hosts on the Internet is to apply for some global IP addresses, but there are not many IPv4 addresses in the world, so one method is network address translation.

Install NAT software on the router connected to Internet on the private network. The router with NAT software is called NAT router. It has at least one valid external global IP address before it can connect with Internet. When all hosts using local addresses communicate with Internet, the local addresses are translated into global IP addresses on the NAT router. In this way, a large number of hosts in the private network can take turns using a limited number of global IP addresses of NAT routers.

Through NAT, you can connect the private network to Internet.

(1) work at the network layer and transport layer

(2) address translation is performed on the passed packet before forwarding

(3) the network address of NAT is bi-directional.

Second, the working principle of NAT router (host A to B communication)

When the NAT router has n IP addresses, at most n hosts in the private network can access Internet at the same time.

The host of the private network cannot be used as a server (imagine that the host on the Internet wants to initiate communication. When the IP Datagram arrives at the NAT router, the NAT router does not know which local host's IP address to translate the destination IP address into).

IV. The working process of NAT router

(1) the intranet computer submits a request for access to the external network to the NAT router

(2) NAT router translates the address of the request packet

(3) the NAT router submits the translation request to the public network server

(4) the NAT router records the mapping in the translation table

(5) the public network server returns the reply packet to the NAT router.

(6) NAT router queries the translation table to obtain mapping information

(7) NAT router translates answer packets

(8) the NAT router should be packaged and returned to the intranet computer after conversion.

Benefits of using NAT to connect the internal network to the external network

(1) Common IP address and network connection, so that the private network shares a public network address to access the Internet

(2) protect the network security by hiding the private network IP address to make it impossible to directly * the private network.

6. Working principle diagram of proxy server

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