TCP/IP protocol

TCP/IP is synonymous with a set of protocols, and it also includes many protocols that make up the TCP/IP protocol cluster.

TCP/IP protocol cluster is divided into four layers, IP is located in the second layer of the Protocol cluster (corresponding to the third layer of OSI), TCP is located in the third layer of the Protocol cluster (corresponding to the fourth layer of OSI).

TCP and IP are the middle two layers of TCP-IP protocol cluster, which is the core of the whole protocol cluster, which plays a connecting role.

1. Interface Layer

The lowest layer of TCP/IP is the interface layer, and the common interface layer protocols are:

Ethernet 802.3, Token Ring 802.5, x., Frame Reley, HDLC, PPP and so on.

2. Network layer

The network layer includes IP (Internet Protocol) protocol, ICMP (Internet Control message Protocol) Control Message Protocol, ARP (address Resolution Protocol) address Translation Protocol, RARP (Reverse ARP) reverse address Translation protocol.

IP is the core of the network layer, and the next hop IP is encapsulated by routing to the interface layer. An IP datagram is a no-connect service.

ICMP is a supplement to the network layer and can be returned to the delivery paper. Used to detect whether the network is unobstructed.

The Ping command sends an ICMP echo packet, which is tested via echo relay.

ARP is a forward address Resolution protocol that finds the MAC address of the corresponding host through a known IP.

RARP is a reverse address Resolution protocol that determines the IP address by MAC address. such as diskless workstations and DHCP services.

3. Transport Layer

The Transport layer protocol is mainly: TCP(transmission Control Protocol) and User Datagram Protocol UDP(subscriber Datagram rotocol).

TCP is a connection-oriented communication protocol, the connection is established through three handshakes, the connection is removed when the communication is complete, because TCP is connection-oriented so it can only be used for point-to-point communication.

TCP provides a reliable data flow service, using "positive confirmation with retransmission" technology to achieve the reliability of transmission. TCP also uses a method called "sliding window" for traffic control, so-called window actually represents the ability to receive, to limit the sending speed.

UDP is a non-connection-oriented communication protocol, UDP data includes the destination port number and the source port number information, because the communication does not need to connect, so it can be implemented broadcast send.

UDP communication does not need to be confirmed by the receiver, is not reliable transmission, it is possible to lose packet phenomenon, the actual application requires programmer programming verification.

4. Application Layer

Application tiers are generally user-oriented services. such as FTP, TELNET, DNS, SMTP, POP3.

FTP (Files Transmision Protocol) is a file transfer Protocol, general upload download with FTP service, data port

Is 20H, the control port is 21H.

Telnet Service is a user remote login service, using 23H port, using the plaintext transmission, the confidentiality is poor, simple and convenient.

DNS (Domain Name Service) is the domain name resolution service that provides conversion between domain names to IP addresses.

SMTP (Simple Mail Transfer Protocol) is simply a message transfer protocol that controls the sending of letters,

Turn.

POP3 (Post Office Protocol 3) is the 3rd version of the Post Office protocol that is used to receive mail.

Data format:

Data frame: Frame header +ip packet + frame tail (frame header includes source and destination host MAC address and type, end of frame is check word)

IP packet: IP head +tcp data information (IP header includes source and destination host IP address, type, lifetime, etc.)

IP data information: TCP header + Actual data (TCP headers include source and destination host port number, shun sequence number, confirmation number, school

Test words, etc.)

TCP/IP protocol