First, IP address and network classification
(1) IP address
We know that different physical network technologies have different addressing methods; the main in different physics networks
Machine, there are different physical network addresses. Internet technology is highly high in different physical network technology
Layer software technology. Internet technology uses a global universal address format for every network of the whole network and
Each host allocates a network address to shield the difference in physical network addresses.
The IP protocol provides an address format for all Internet networks, and is assigned under unified management.
One address corresponds to a network host (including gateway), which is the difference between the physical address by the IP layer
shield. The address used by the IP layer is called the network address and is also a IP address. It by the network number and host
The two parts are composed, all hosts in the unified network use the same network number, and the host number is unique.
The IP address is a 32-binary number, divided into 4 fields, 8 bits per field.
(2) Three types of major network addresses
We know that from LAN to WAN, different types of network scale varies greatly, and must take a difference. therefore
According to the size of the network, the network address is divided into three types, as shown in the figure:
Category A: 0 1 2 3 8 16 24
31
0
Network number
Host number
Class B:
1
0
Network number
Host number
Class C:
1
1
0
Network number
Host number
Class A address is used for a small number of large networks larger than 216, each Class A network
Hand up to 224 hosts; Class B address is used for host numbers between 28-216, there are not many numbers
Medium network, Class B network up to 214; Class C addresses can only accommodate 28 hosts per network
Summary net, Class C network up to 221.
In addition to the three primary types of the three main types of A, B, and C, there are two other types of addresses, as shown:
Class D:
1
1
1
0
Multicast address
Class E:
1
1
1
1
0
Reopeize
Among them, multicast address is a multi-point transmission address slightly weaker than broadcast addresses.
Metal transmission technology is supported. The E-address is used for future extensions.
(3) TCP / IP regulations
In addition to a host, the network address is also a special form of special forms.
* Broadcast address
TCP / IP stipulates that the network address of the host number is "1" is used for broadcast use, called broadcast addresses.
The so-called radio refers to sending messages to all hosts to the Internet.
* Limited broadcast
The broadcast address mentioned earlier contains a valid network number and host number, which is technically called direct broadcast.
(Directed Boradcasting) Address. Anything on the Internet online can be used to any other net
Many direct broadcasts, but there is a shortcoming in direct broadcasting, that is to know the network number of the Subtock Network.
Sometimes it is necessary to broadcast within this network, but I don't know the network number. TCP / IP regulations, 32 ratios
Extremely "1" network network address is used for this broadcast, this address is called a limited broadcast address (Limited
Broadcast address.
* "0" address
The TCP / IP protocol stipulates that all the network numbers that are "0" are interpreted as "this" network.
* Return address
Class A network address 127 is a reserved address for communication between network software tests and local machine processes.
Called with a loopback address. Regardless of the program, once the return address is used, the protocol software returns now, and no network transmission is not performed. TCP / IP protocol regulations, one, including
The grouping of the network number 127 cannot appear on any network; Second, the host and gateway cannot broadcast the address
Any finding information.
It can be seen from the above provisions that the host number "0" "1" address is special in the TCP / IP protocol
Meaning, cannot be used as a valid address of a host.
