Study notes for online learning, record some study points.
1. The five-layer model of the network: from bottom to top: physical layer, link layer, network layer, transport layer, application layer.
2. Physical layer: The physical layer connects the computers: it can be a fiber optic cable, wireless signal, etc., transmitting 0 and 1.
3. Link layer: mainly the Ethernet protocol, which defines a frame, that is, a group of electrical signals. The protocol header records the MAC addresses of both parties (the unique identifier of the hardware network card, the first six digits are the manufacturer id, and the last six digits are the manufacturer's internal flow id) and other protocol information. The MAC address is generally obtained through the ARP protocol.
4. Network layer: IP protocol, which combines countless sub-networks into the entire Internet. The IP address is mainly obtained from the network provider through the DHCP protocol. Communication between hosts is defined. IP address = network number + host number, and the network number and host number are divided by the subnet mask.
5. Transport layer: TCP protocol (high reliability) and UDP protocol (fast speed). Communication is established by IP address plus port (socket). Through the port, the control of both sides of the network transmission is accurate to the process and thread of the host.
6. Application layer: various custom protocols, such as http, ftp, etc.
7.DHCP: Dynamic Host Configuration Protocol, which is mainly used for centralized management and allocation of IP addresses, which realizes the automatic allocation of IP addresses without the need for users to set them by themselves.
8. ARP: Address Resolution Protocol, mainly used to manage the mapping relationship between IP addresses and MAC addresses. There is generally a cache of the mapping relationship between IP addresses and MAC addresses on the host. Generally , the MAC address is obtained through the IP address. If there is no cache to change the mapping, the data packet request is broadcast and sent in the local area network, and each host compares its own IP address. Whether it is consistent with the IP in the data packet, if it is consistent, it will reply its own MAC address, otherwise the request will be discarded.
9. DNS Domain Name System: A distributed system used to convert domain names into IP. It is divided into root domain name server, top-level domain name server, authority domain name server, and local domain name server. For example, to visit www.baidu.com locally. It is first parsed by the local domain name server, then sent to the root domain name server, then sent to the given - level domain name server (com server), and then sent to the authority domain name server (baidu server), returning ip.