Computer network-basic concepts of Network

(1) Basic Concepts

DNS (Domain Name System): domain name system, which establishes the IP ing between domain names and IP addresses.

HTTP (HyperText Transport Protocol): Hypertext Transfer Protocol (Hypertext Transfer Protocol) is an object-oriented protocol at the application layer. It is applicable to distributed hypermedia information systems in a simple and fast manner.

IP packet format: Header + data, header = Fixed part + Option part, fixed part 20 bytes, maximum length is 60.

Frame format: Destination Address + Source Address + Type + Data + FCs

(2) TCP three-way handshake

(1) TCP three-way handshake process: host a sends a connection request to host B; host B confirms the received packet segment of host; host a confirms host B again.
(2) The three-way handshake is used to prevent the invalid connection request packet segment from being suddenly transmitted to host B, thus generating an error. Invalid Connection Request Message segment means that the connection request sent by host a has not been confirmed by host B, so after a period of time, host a re-sends a connection request to host B, data transmission is completed in sequence. In this special case, the connection request sent by host a for the first time is not lost, but is delayed to reach host B Due to network nodes. Host B considers it a new connection initiated by host, therefore, host B agrees to the connection and sends the confirmation to host a. However, host a does not care at this time, and host B has been waiting for host a to send data, resulting in a waste of resources on host B.
(3) The two handshakes fail because of the special circumstances of the actual connection request described above.

(3) ARP Address Resolution Protocol

(1) The sender host saves the ARP buffer list, indicating IP address and MAC address ing.

(2) Before sending data at the physical layer, query the ARP buffer list and query the MAC address based on the IP address. If no ARP packet is sent to all hosts

(3) When an ARP packet is sent to another host, it determines whether it belongs to the specified IP address. This means that the broadcast informs the sender of its MAC address.

(4) The sender updates the ARP buffer list, adds the ing from the IP address to the MAC address, and sends data to the MAC address.

(4) ARP Virus

The third step of ARP Address Resolution is to pretend that you are the IP address and frequently tell the sender that I am the IP address you are looking for and ask the sender to update the ARP buffer list, this API intercepts the data sent later.

Computer network-basic concepts of Network