As we know, the Internet is a communication network formed by global computers as a whole. The connection between two computers communicates with each other in the network, and the data packets they send will contain some additional information, which is the address of the computer that sent the data and the address of the computer that received the data. Every computer that likes to communicate easily has a similar pre-assigned telephone number, which is used to identify the address in our daily life. This is how the address symbol of IP address is introduced. According to the TCP/IP protocol, the IP address is a 32-bit binary number, which is only within the scope of the Internet. For example, the IP address of a computer connected to the Internet:
1 10 100 10 0 100 100 1 1000 1 100 000000 10
Obviously, these figures are a good memory. In order to facilitate people's memory, the 32-bit binary of the computer IP address will be divided into four segments, separated by decimal points, and then every eight segments will be converted into decimal numbers, so that the computer IP address will become: 2 10.73. 140.2.
IP address classification
We have made it clear that the Internet is a large-scale interconnected network. There are many networks in the world, and each network computer is uniquely identified by its own IP address. Based on this, we can imagine that on this huge Internet, each network has its own identification code. Very similar, in our daily life, such as a telephone number, the first four digits of the telephone number 05 15 163 indicate which region the mobile phone belongs to, and the latter digits indicate the telephone number of the region. Similar to the above example, the IP address of the computer is also divided into two parts, namely the network ID and the host ID. All hosts on the same physical network use the same network identification, and all hosts in the network (including workstations, servers and routers on the network) have corresponding host identification? The 4-byte IP address is divided into two parts, one part is to determine the specific network segment, that is, the other part is to determine the host identification of a specific node, that is, the specific network computer number. For example, the IP address of Yancheng Information Network Center Server is 2 10.73. 140.2, and the IP address can be divided into two parts: network ID and host ID, so that the IP address can be written as:
BR/>； Network logo: 2 10.73. 140.0
Host ID: 2
Write together: 2 10.73. 140.2.
Because there may be different computers in the network, some networks may contain more computers, and some networks may contain fewer computers, according to the size of the network, the 32-bit address information is set to be three-thirds, corresponding to Class A, Class B and Class C IP addresses respectively.
1。 Class a IP address
One type of IP address refers to the network number of the IP address in the first four digits, while the other three parts are all on the local computer. If the IP address is expressed in binary form, the most important bit of the network address must be "0", which consists of a 3-byte network address of 1 byte and a Class A IP address of the host address. The length of network identification of 7 hosts with Class A IP addresses determines that 24 classes can be used in large networks with more than 6,543,800 hosts and fewer network addresses.
2。 Class b IP address
The first two digits, four digits IP address and network number of Class B IP address. Class B IP address consists of 2 bytes of the host address of a 2-byte network address, and the highest bit of the network address is "10". Class B IP addresses identify the length of the network 14. Hosts identified by 16 B network addresses are suitable for medium-sized networks, and each computer network can accommodate more than 60,000 computers.
3。 Class c IP address
Class C IP address refers to a four-digit IP address. The first three segments of an IP address are the network number, and the rest of the periods are located on the local computer. Binary IP address. Class C IP address consists of a 3-byte network address and a 1 byte host address. The most significant bit of the network address must be "1 10". Class C IP address identification length is 8, and a large number of Class C network addresses are suitable for small-scale local area networks. The 254 computers in each network can only contain one network with a maximum length of 265,438+0 hosts.
In addition to the above three types of IP addresses, there are several special types of IP addresses. According to TCP/IP protocol, the address "lll0" in the first byte of an IP address is called a multicast address. Therefore, if the first byte is greater than 223 and less than 240, the IP address is the IP address corresponding to the multicast address ("0.0.0.0") of the current host. The IP address of each byte ("255.255.255.255") is the address of the broadcast address of the current subnet. Any IP address of llll0 is reserved for future use as a special destination IP address. The beginning cannot be decimal "127", 27. 1. 1.6558.
Network addressing rules
The network address must be unique.
B, 127 logo. Class A address, number 127 is reserved for internal loopback function.
C, the first byte of the network identifier cannot be 255. The number 255 is used as the broadcast address.
D the first byte of the network identifier cannot be "0", which means that the address was not sent by the local host.
2。
Host addressing rules that must be unique host ID are in the same network.
B. Each bit of the host identifier cannot be "1" at the same time. If all bits are "1", the machine address is the broadcast address, not the host of the address.
C, each bit of the host identifier need not be "0". If each bit is "0", it means "media, network only", not any host in the network.
, IP subnet mask overview
1。 Mask concept of subnet
A part of the subnet mask, a 32-bit address, is used to mask the IP address and interpretation to distinguish the network ID from the host ID, and the IP address is on the local area network or online remotely.
2 Determine the subnet mask
A digital subnet mask consists of the number of possible subnets and the number of hosts in each subnet. The original subnet number and host number must be consistent with the previous custom subnet mask.
To customize the subnet mask, follow these steps:
We use it to determine the group address. For example, we applied for the normalization of the network number "2 10.73". Ab ",class C IP address, the network address with the network identification of" 2 10.73 "and the host identification of" AB ".
B, according to the subnet number, the number of extended subnets that may appear in the future, and some bits of the host, define the subnet mask. For example, we need 12 subnet now, and we may need 16 subnet in the future. The subnet mask determined by the first and third bytes of the first four bytes. The number 4 is set to "1", that is, "1110000" in the third byte. Let's call it a new binary subnet mask.
C. The sum of each bit corresponding to the initial network is set to "1", that is, the first two bytes are set to "1" and the fourth byte is set to "0". Intermittent binary form of mask:11111.1165438+.
D will be in intermittent decimal form: "255.255.240.0"
The number of subnet masks for this network.
3.IP mask label
Marking method network
The IP address of a network without children can be written as a host number 0 mask. If the IP address is 2 10.73. 140.5 and the subnet mask is 255.255.255.0, the default mask is to write only the IP address.
b，
Subnets marked with subnets must appear in pairs. For example, a class C address.
The first three bytes of 1.IP address indicate the network number, and the last byte indicates the subnet number and host number, and whether the two IP addresses belong to the same network segment. If they belong to the same network time interval, the information exchange between these two addresses does not go through the router. If they don't belong to the same network range and have different subnet numbers, they need to exchange information between the two addresses through the router. For example, the host IP address of 2 10.73. 140.5 is the host with host ID 000010, 210.73.140.16. This shows that the two IP addresses are in the same network area, and the information exchange between the two hosts needs to go through the router's host ID 10. 73. 60. 1, 00000 1, 210.73.60.2521. Network, exchange information through routers. Its subnet hosts are 1 and 252.
2。 Subnet screening function, there are multiple subnets, and the subnet number can only be expressed as a range. If you don't specify the subnet number and subnet mask format (class C address), you can't talk about the specific subnet mask completely:
V. Intellectual property matters
1。 Under normal circumstances, the network of the Internet Information Center is assigned an IP address, so only when the network address is involved, statements of Class A, Class B and Class C are used;
2。 The assigned network address and network identification are fixed, and the computer identification can be changed within a certain range. The following are the forms of three network addresses in the combination:
Class a address: 73.0 .0.0
Class b address: 160. 153.0.0.
Class C address: 2 10.73. 140.0.
You can change each 0 between 0 and 255.
It is decided that because the first three bits are all types of networks, Class A network addresses are no longer divided into Class B IP addresses, one IP address of Class B IP addresses and one IP address of Class C IP addresses.
When it comes to the IP address of a specific computer, don't use the expressions of Class A, Class B and Class C. You can say which A, B and C network the host address belongs to.
Through the above study, we must know the IP address. Using IP address, you can send e-mail to the Internet and get it, for example, WWW service, BBS service, FTP service, etc.
References:/question/459513.html.