Analysis of the establishment and release of TCP connections using the Tcpdump capture packet under Linux

I use the environment for the WIN7 64-bit flagship version under the VirtualBox installation of the centOS6.5 experimental environment

Establish a connection

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In Terminal 1, enter root permissions, type tcpdump tcp-vx-i eth2

#使用man手册查看tcpdump的使用方法

#eth2为接口, you can use ARP-A to display the current interface

In Terminal 2, type telnet www.baidu.com

#远程登录www. Baidu.com 80 Port

Information about the connection pack that appears in Terminal 1, such as

The figure contains three packages:

1. From the local computer to the remote, the flag is [S], that is, set SYN, establish the connection, SEQ is 1189337464

2. From the remote to the local computer, the flag is [S.], that is, the SYN is set, see the ACK value is 1189337465, is the remote response to the local computer to establish a connection requirements

3. From the local computer to the remote, ACK value is 1, three handshake is completed

Release connection

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Type Ctrl +] in Terminal 2, and exit Telnet

The unpacking information begins to appear in Terminal 1, such as

The figure contains 4 packets, and the analysis packet can be found

Analysis of the establishment and release of TCP connections using the Tcpdump capture packet under Linux