OSI- transport layer
Port number (2 bytes
SYN（1bit）
ACK (1bit)
Session multiplexing (Why is an IP address can do a lot of things?)
Source port address can be different
Quintuple (not the same two quintuple world)
Source IP address - destination IP address - a source port number - destination port number - protocol number
port
0-65535
0-1023 well-known port
1024-65535
| The port number | application | Chinese name | protocol |
|---|---|---|---|
| 20/21 | FTP | File Transfer Protocol (transfer of large files) | TCP |
| 22 | SSH | Remote management application (security, encryption) | TCP |
| 23 | telent | Effective remote protocol (insecure) | TCP |
| 25 | SMTP | Simple Mail Transfer Protocol (just mail) | TCP |
| 53 | DNS | Domain Name Resolution Protocol | UDP/TCP |
| 69 | TFTP | Transfer small files | UDP |
| 80 | HTTP | Hypertext Transfer Protocol | TCP |
| 110 | POP3 | recieve email | TCP |
| 161/162 | SNMP | Network Management Protocol | UDP |
| 179 | BGP | Exterior Gateway Routing Protocol | TCP |
| 443 | HTTPS | (HTTP + SSL) secure http | TCP |
| 520 | RIP | Dynamic routing protocols | UDP |
| 521 | RIPng | The next generation of dynamic routing protocols | UDP |
The reliability of TCP
reliability of the foundation
1. Data transmission is ordered
2. The data transmission is the acknowledgment mechanism
3. The data retransmission mechanism
4. Reliability premise is to establish a connection
TCP three-way handshake
1. The first handshake: Client Sever tries to establish a connection, a randomly generated sequence number seq = j, the SYN flag bit is set to 1, and the data packet to Server, Clinet enters the SYN_SENT state, waiting for acknowledgment Sever.
2. The second handshake: Sever Client wants to know the received packet to establish a connection, SYN flag is 1 and the other indicates a request to establish a connection, ACK flag is 1 agree to establish a connection, ack = J + 1, client terminal seq I want to send data to tell you the hair of x, x server sends + 1 is to tell the other side, you send the packets x I have received (confirmation effect), x + 1 from the next time it began to send sEQ ID NO own randomly generated seq = K, Server enters SYN_RCVD state.
3. Third handshake: the Client receives acknowledgment, checking whether the ack J + 1, ACk is 1, then if the correct ACK flag is set to 1, ack = K + 1, K represents the data received before , sends the data packet to the Server, ack Server checks whether K + 1, aCK is set, and if correct, the connection is established, Server, and Client enters the eSTABLISHED state, complete the three-way handshake, then transmission can begin between Client and Server the data.
Specific reference blog https://www.cnblogs.com/Qing-840/p/9283367.html