IPv4 dotted decimal number into five, medium and small to adapt to different network types, different classes of bits used to represent the network and the difference between the number of bits used to represent the host. This is five:
• Class A addresses
• Class B addresses
• Class C addresses
• Class D address
• Class E addresses
wherein:
• Class A addresses: the first octet address in a Class A bit network, and the network position the first bit is always expressed 0,1-7bit network identifier, i.e., the total of the format: 0 ××××××××. After three octets host bits represented by a class A address format can know the network address of the identified class A valid range is 00000001 - 011111111, expressed in decimal 1.0.0.0 to 126.0.0.0 i.e. a total of 64 + 32 + 16 + 8 + 4 + 2 + 1 = 127 possible class a network, the host 24 identifies two power minus 2 (to remove all-zero and all-1's address). I.e., the number of each network host 16777214, this type of support giant network address, typically assigned to a network having a large number of hosts.
Technically 127.0.0.0 is a class A address, but he has been retained as a closed loop (look back) test can not be assigned to a network. TCP / IP protocol provides a packet containing the network 127 can not appear on any network; two, hosts and gateways can broadcast routing information for any address.
• Class B addresses: the first two octets of network address in a Class B bits, and the first two bits are always a bit 10,3-15bit network represents a network identifier, i.e., a total of the format: 10 ×××× ×× ××××××××. After two octets bit indicates the host, the format B may know the network address class identifier class B address valid range is 1,000,000,000,000,001 1,011,111,111,111,110 ~, i.e. in decimal 128.1.0.0 ~ 191.254.0.0, host identification number 16 is a power of 2 minus 2 (to remove all-zero and all-address 1). That number is 65534 for each network host, these addresses are generally assigned to medium-sized networks.
• Address Class C: Class C address before three octets represent the network bits, and the first three bits always 110,4-23bit bit network represents a network identifier, i.e. a total of format: 110 ××××× ×××××××× ××××××××. After a bit octet indicates the host, the format of the class C address identifies the network can know the effective range of the class C address 11000000 ~ 11011111 1,111,111,111,111,110 0,000,000,000,000,001, i.e. 192.0.1.0 ~ 223.255.254.0 represented in decimal, so the effective network number 2097152. Host identification number is 8 2 power minus 2 (to remove all-zero and all-1's address). I.e., the number of each network host 254, such address is generally assigned to the small-scale networks.
• Class D addresses: a multicast (Multicasting, also known as multicast broadcast) in the IP network, the first four bit set constant at 1110. A multicast address is a unique network address. It guide packet reaches a predefined set of IP addresses, such a machine can simultaneously transmit data to multiple receiving end, the receiving end so that each ratio create a different stream effectively reduces network traffic. Because Class D address for a private network multicast packet to the IP address of the end system defined group, but not for interconnecting the separate end system or network, there is no need to address the octet or separate address bits to represent the network host and, on the contrary, the entire address space is used to identify a group IP address (either a, B or class C address). The scope of the Class D address space of 224.0.0.0 to 239.255.255.254.
• E Class address: used to be reserved for the study of the IETF, the Internet is not available Class E address. 4 before the constant bit set to 1111. Effective address range 240.0.0.0 to 255.255.255.255
in IP address range, and some non-routable address. IANA (Internet Assigned Numbers Authority) reserved as part of the address to a private IP address space specifically for use inside the LAN, the following address:
A class of addresses: 10.0.0.0 ~ 10.255.255.255
Class B addresses: 172.16.0.0 ~ 172.31.255.255
Class C addresses: 192.168.0.0 ~ 192.168.255.255
The Internet address will not be assigned, they also never be routed on the Internet, although they are not directly connected to the network and the Internet, but can still be used and Internet communications, we can choose the appropriate address classes as needed, in the internal LAN addresses as public IP addresses as used. On the Internet, those devices do not need to communicate with the Internet, such as printers, managed hubs, etc. You can also use these addresses to save IP address resources.