<>IP the address is ? effect

IP the address is IP A unified address format provided by the protocol , It assigns a logical address to each network and host on the Internet , To shield the difference of physical address . common IP address , Divided into IPv4 And IPv6 Two categories
IPv4 The address is expressed in dotted decimal ,X.X.X.X (X It means a 10 Base ) example :192.168.1.1
every last X Corresponding to 8 Binary , Count Reg 32 bit; every last X corresponding 1 Bytes ;X The value range is 0 --255 ;
structure : Network bit + Host bit
IP Address is used to uniquely identify an online device within a certain range ;( All devices that need internet access , Must have IP address )

<>IP Address classification (IPv4)

IP Addresses fall into five categories , The number of addresses that can be accommodated is different :
A Class reserved for government agencies (0.0.0.0 reach 127.255.255.255)
B Class assigned to medium-sized companies (128.0.0.0 reach 191.255.255.255)
C Class is assigned to anyone who needs it (192.0.0.0 reach 223.255.255.255)
D Class for multicast (224.0.0.0—239.255.255.255)
E Class for experiments (240.0.0.0—247.255.255.255)
A,B,C Among the three categories IP address = network address + Host address , and D,E The two types do not distinguish between network address and host address
Special instructions :
(1)A In class 10.X.X.X Is a private address ;127.X.X.X Is a reserved address
(2)B In class 172.16.0.0~172.31.255.255 Is a private address
(3)C In class 192.168.X.X Is a private address

<> Subnet mask

Network address can be simply understood as network segment , The host address is the address of the corresponding different hosts in the network segment .
Subnet mask is used to distinguish IP Network bit and host bit in address , Must be with IP address , One to one correspondence , Appear in pairs ;
Subnet mask and IP The same address is 32 Bit address , Then IP The network address can be obtained by summing the address and subnet mask ( Network segment ).
In subnet mask 1 Corresponding IP Bits in address , Call it network bit ;
In subnet mask 0 Corresponding IP Bits in address , Called host bit .
Subnet mask characteristics :

* And IP Address to address correspondence ;
* 1 and 0 Always continuous , Will not cross ;
* Always on the left 1, Always on the right 0;
e.g. IP Address is 192.168.10.2, Subnet mask is 255.255.255.240. Binary representation : IP address : 11000000 10101000
00001010 00000010 Subnet mask : 11111111 11111111 11111111
11110000( indicate IP Address before 28 Bit indicates network bit , after 4 Bit is host bit ) IP The address and mask are summed : 11000000 10101000 00001010
00000000 So this IP The network where the address is located is 192.168.10.0, Host ID is 2.
An address :XX.XX.XX.128/25,/25 Is another form of mask , Indicates continuous 25 individual 1, Remaining use 0 Supplement .
(1) Host number : Host number + network number =32,32-25=7
(2) network address : When 7 Bit host numbers are all 0, that is XX.XX.XX.128
(3) Broadcast address : When 7 Bit host numbers are all 1, that is XX.XX.XX.255
(4) Number of available addresses :7 Bit host number yes 2 7 2^7 27 Kinds of results , But remove the network address and broadcast address , Namely : 2 7 − 2 = 126 2^7-2=126 27−2=
126, That is, there can be 126 Hosts .

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