Computers on the Internet must identify each other's identity in a mechanism to facilitate communication. In the second floor of the online seven-layer architecture, this mechanism is the online card hard body order (MAC address), which is represented by 6 Bytes, it looks like 00-0F-00-0A- E4-80, the top three yuan groups are the code of manufacturers, and the three bit groups behind are the factory number of the network card, and the MAC address of each online card must be the only worldwide. This mechanism is the SMB protocol in the top of the seven layers. Under UNIX, use HostName, use NetBIOS Name in the Windows network, this name is used for internal network, as long as the name in the same network is unique, in other words, the same name can be used Different domains. This mechanism is IP in a third layer in the seven layers. IP is composed of 32 positions, separated by (.) Per 8 bits, which looks like 163.21.236.71 in ten. Like the MAC site, IP of each computer must also be unique worldwide. Due to the popularity of TCP / IP in the network world, it makes IP addresses the most important identification mechanism. The formulation and verification of IP is managed by the NIC organization. They divide the 32-bit yuan of IP into four bits groups, and the order level is set, and the number of networks according to the number of copies is divided into four, B, C, and D. grade. Taking the Taipei Education Network as an example, the Ministry of Education will apply to the NIC's IP to Taipei Education Network, a set of Class B 163.21.xx, Taipei Education Network Center, then divides it into a plurality of groups Class C 163.21. 1.x ~ 163.21.254.x, designated to each school, some university colleges can be divided into multiple Class C, and smaller schools are divided into half Class C or quartzte Class C. To identify a computer on the Internet, just know its IP, but if you want to identify a group of computers, it is more troublesome, you must expressed in a network start IP and a network mask. For example: 163.21.236.0/255.255.255.0 represents the network of the author. Where the start IP is used to identify a network (a group of computers), it is generally referred to as a network number. This IP is not available. The network mask is used to indicate the size of the network. The network size refers to the number of computers that can accommodate the network, for example: 255.255.255.0 is that there can be up to 254 computers in the network, such as 255.255.255.128. It means that there can be up to 126 computers in the network. The network mask and IP address can be brought to the IP, which can be judged that the IP is a computer belonging to which network. For example: 10100011 00010101 11101100 01000111 = 163.21.236.71 111111 11111111 111111 00000000 = 255.255.255.0 ---------------------------------------------------------------------------------------- -------------------------------------------------- ------- 10100011 00010101 11101100 00000000 = 163.21.236.0 Take the IP 163.236.71 and Internet mask 255.255.255.0 at 163.21.236.71, to obtain a bitmine and operation of 163.21. 236.0 This value, so the computer is a computer within 163.21.236.0. Since the network mask 255.255.255.0 has a total of 24 from the left to the left, there is a simple use of 24, so 163.21.236.0/255.255.255.0 can be simply expressed as 163.21.236.0/24.
