Summary of written examination questions of safety company

One IP address (note definition of address range and private address)

The IP address is divided into five categories, Class A is reserved for government agencies, Class B is assigned to medium-sized companies, Class C is assigned to anyone who needs it, Class D is used for multicast, Class E is used for experiments, and the number of addresses can be accommodated varies. A, B, c Three characteristics of IP address: When the IP address written in binary form, a class address is always 0, the first two bits of class B address always 10,c the first three digits of the class address is always 110.Class A address(1) A class address 1th byte is the network address, the other 3 bytes are the host address. 　　The first digit of its 1th byte is fixed to 0. (2) Class A address range: 1.0.0.0---127.255.255.255 (3) The private address and reserved address in Class A address: ① 10.x.x.x is a private address ( the so-called private address is not used on the Internet, and is used in the 　　c6> address in Local area network). The range (10.0.0.0---10.255.255.255) ②127.x.x.x is a reserved address, used for cyclic testing. Class B address(1) Class B address 1th byte and 2nd byte is network address, the other 2 bytes is the host address. 　　The first two bits of its 1th byte are fixed to 10. 　　(2) Class B address range: 128.0.0.0---191.255.255.255. (3) The private address and reserved address of Class B address ①172.16.0.0---172.31.255.255 is a private address ②169.254.x.x is a reserved address. If your IP address is automatically obtained by IP address, and you do not find an available DHCP server on the network. 　　You will get one of the IP. 191.255.255.255 is a broadcast address and cannot be assigned. Class C Address(1) Class C address 1th byte, 2nd byte and 3rd byte are network address, 4th byte is host address. 　　In addition, the first three bits of the 1th byte are fixed to 110. 　　(2) Class C address range: 192.0.0.0---223.255.255.255. (3) The private address in the Class C address: 192.168.x.x is a private address. (192.168.0.0---192.168.255.255) Class D address(1) Class D address is not divided into network address and host address, its 1th byte of the first four bits fixed to 1110. (2) Class D address range: 224.0.0.0---239.255.255.255 Class E Address(1) Class E addresses are not divided into network address and host address, its 1th byte of the first four bits fixed to 1111. (2) Class E address range: 240.0.0.0---255.255.255.255 IP address if only use ABCDE class to divide, can cause a lot of waste: a network of 500 hosts, cannot use C class address. However, if a class B address is used, only 500 of the 60,000 + host addresses are used, resulting in a large waste of IP addresses. 　　Therefore, the IP address also supports VLSM technology, which can be further divided into subnets on the basis of ABC Class network. No class address

In addition to the ABCDE of IP address segment, such as: 192.168.1.0 255.255.255.252, etc. divided into C-segment address

This paper briefly describes how the TCP protocol can ensure the reliability of data packet in the process of transmitting and receiving.
For:
(1) In order to ensure the reliable transmission of packets, the sender must keep the packets sent in the buffer;
(2) and start a timeout timer for each sent packet;
(3) to release the buffer occupied by the other party if it receives an answer message from the other person (either an answer to this package or an answer to a subsequent package in the package) before the timer times out;
(4) Otherwise, retransmit the packet until the maximum number of times the answer or retransmission is received.
(5) When the receiving party receives the packet, CRC check first, if the correct data to the upper layer protocol, and then send a cumulative answer package to the sender, indicating that the data has been received, if the receiver just have data to send to the sender, the answer package can also be in the packet in the past.