Public IP

Public network, the network access the Internet are two ways.Public network access: access to the Internet to get the IP address of the computer is non-reserved address on the Internet. Public network of computers and other computers on the Internet can easily access each other.
 NAT (Network Address Translator) is a network address translation, it is within the topology to achieveNetwork IP address and public network addresses and vice versa, a large number of internal IP addresses to one or a small number of public IP addresses, to reduce the public IP address of the occupation. NAT is the most typical applications are: in a LAN, only one computer connected to the Internet, you can use NAT to share Internet connection, so that other computers within the LAN can access. Using the NAT protocol, LAN computer can access the Internet on computers, but computers on the Internet can not access the LAN computer.
Windows operating system, Internet connection sharing, sygate, winroute, unix / linux software such as the natd are using NAT to share Internet connection protocol. All ISP (Internet Service Provider) to provide Internet access within the network mode, almost all NAT-based protocol.Specific operationsAnalogy with the mail system. A public network ip, equivalent to saying that you have a detailed address, you can send someone else to write, others can also use this address for all communications with you.
 Now take a look at the internal network ip is not what the situation. It's like living in a large yard, all incoming and outgoing e-mail forwarded by the janitor's room. If an ordinary e-mail, can be placed on the janitor's room, janitor's uncle aunt to see you will turn to you, or you go to the janitor's room to see, this is not important, anyway, even after a little twists and turns, you can still see to the message. Now assume the following if you come to a registration, post office staff said: I must sign. Janitor's uncle say: I'm sorry, I have to go through all the mail transit ~. So the post office staff had to take the letter back ... ...The actual situation and the almost, so there is no public network ip, that your machine is not directly connected to the internet, but all communication through a proxy (usually transparent gateway) for transit, this time the problem came, it will Some communications can not be smooth in this mechanism. Such as between two Internet cafes, Internet cafes machine ip is not a typical example of public network, usually between two Internet cafes can not transfer files to each other through QQ. Another example is no public network ip, play online games usually play against the problem, you build the game so that others can not join.Public network ip addressClass A: 1.0.0.0 to 126.255.255.255 primarily allocated to a large number of hosts and the small number of large local area network networkClass B: 128.0.0.0 to 191.255.255.255 are generally used for international companies and government agenciesClass C: 192.0.0.0 to 223.255.255.255 for general small companies and other research institutions CampusClass D: 224.0.0.0 to 239.255.255.255.0 for special purposes, also known as the radio addressClass E: 240.0.0.0 to 247.255.255.255 retainPrivate ip addressThese types of addresses as private addresses the followingClass A: 10.0.0.0 to 10.255.255.255Class B: 172.16.0.0 to 172.31.255.255Class C: 192.168.0.0 to 192.168.255.255127.0.0.0 to 127.255.255.255 which loopback address for the system