Shulou(Shulou.com)06/03 Report--

Common Ports and Services

21/tcp FTP File Transfer Protocol

22/tcp SSH Secure Login, File Transfer (SCP), and Port Redirection

23/tcp Telnet Unsecure text transfer

25/tcp SMTP Simple Mail Transfer Protocol (E-mail)

53. Dns Service

67, 68 dhcp server, client

69/udp TFTP Trivial File Transfer Protocol

79/tcp finger Finger

HTTP Hypertext Transfer Protocol (HTTP)

88/tcp Kerberos Authenticating agent

110/tcp POP3 Post Office Protocol (E-mail)

113/tcp ident old identification server system

119/tcp NNTP used for usenet newsgroups

123 NTP Network Time Protocol

220/tcp IMAP3

443/tcp HTTPS used for securely transferring web pages

1521Oracle

3306MySQL

Seven-layer and four-layer network models

Osi Level 7:

Application Layer-Presentation Layer-Session Layer-Transport Layer-Network Layer-Data Link Layer-Physical Layer (Layer 1)

TCP/IP layer 4

Application Layer (Application Layer, Presentation Layer, Session Layer)-Transport Layer-Network Layer-Link Layer (Data Link Layer and Physical Layer)

TCP3-way handshake establishes connection

In TCP/IP protocol, TCP protocol provides reliable connection service, using three-way handshake to establish a connection, as shown in Figure 1.

(1)First handshake: When establishing a connection, client A sends a SYN packet (SYN=j) to server B and enters SYN_SEND state, waiting for server B to acknowledge.

(2)The second handshake: Server B receives the SYN packet and must acknowledge the SYN(ACK=j+1) of client A. At the same time, it also sends a SYN packet (SYN=k), i.e., SYN+ACK packet. At this time, server B enters the SYN_RECV state.

(3)Third handshake: Client A receives SYN+ACK packet from server B and sends ACK packet (ACK=k+1) to server B. After sending this packet, client A and server B enter ESTABLISHED state to complete the three-way handshake.

The three-way handshake is completed and the client and server begin transmitting data.

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