The connection of intranet IP extranet IP and the principle of accessing Internet

First, explain the concept of "intranet" and "Extranet":

Intranet: That is to say the LAN, such as the school's local area network, the local area network each computer IP address in this local area network has the mutual opposite sex, is not repeatable. But the intranet IP in two LAN can have the same.

Extranet: That is, the Internet, LAN through a server or a router external connection network, this IP address is unique. That is to say, all computers in intranet are connected to this one extranet IP, through this one external IP external exchange data. In other words, a local area network of all computers in the intranet IP is not the same, but the common use of an external network IP. (using Ipconfig/all to find the IP is your local intranet IP; What you see on www.ip138.com is the IP you use to connect to the Internet, that is, the extranet).

In the LAN, each computer can allocate its own IP, this IP is only valid in the LAN. And if you connect the computer to the Internet, your network provider (ISP) server will assign you an IP address, which is the IP address of your external network. Two IP exist at the same time, one internal, one external.

When you buy two computers in your home, you want to set up a local area network, you have to use network cable and router and other devices to connect two computers, you will also have two sets of computer fixed IP, For example, computer a set to 192.168.1.2, Computer B is set to 192.168.1.3, so you can use these two IP addresses to each other to access two computers, but these two IP addresses only between the two computers, the external network is not valid. Therefore, the IP allocated in the LAN has no correspondence with the IP in the WAN.

You are in the intranet in the Internet, are in the gateway to send a request, and then by the gateway (generally for routers) with the external network IP to the int online, after receiving data, then distributed to your intranet IP.

For example: The gateway is your school gate, to the outside, your extranet IP is your school gate number. But inside your school, you are a few units several floors several dormitory (namely intranet IP). The thing you want to send, first pass the school gate (Gateway). Take back the thing is also only wrote the school number (extranet IP). Then the concierge received the arrival, and then according to your dorm room number unit number (that is, intranet IP) sent to your door. The following figure:

Internet IP (i.e. extranet IP) address unification is managed by an organization called "IANA" (internetassigned numbersauthority, internet network number distribution agency).

Due to the unreasonable distribution and the limitations of the IPV4 protocol itself, the IP address resources of the Internet are getting more and more tense, in order to solve this problem, the IANA will retain part A, B and Class C IP address for the use of LAN.

IP address space:

Class A network

10.0.0.0~10.255.255.255

Class B Network

172.16.0.0~172.31.255.255

Class C Network

192.168.0.0~192.168.255.255

In other words, if you find the IP address in the above a, B, c range of IP address, it must be the IP address of the local area network, otherwise it is the address of the WAN.