语法：
tcpdump [options] [Protocol] [Direction] [Host(s)] [Value] [Logical Operations] [Other expression]
Protocol(协议)：
Values(取值)：ether,fddi,ip,arp,rarp,decnet,lat,sca,moprc,mopdl,tcp and udp.
If no protocol is specified, all the prorocols are used
Direction(流向)：
If no source of destination is specified,the "src or dst" keywords are applied.(默认是src or dst).
For example, "host 10.2.2.2" is equivalent to "src or dst host 10.2.2.2".
Host(s)(主机)：
Values(替代关键字)：net,port,host,portrange.
If no host(s) is specified, the "host" keyword is used.默认如果此段没有指定关键字，默认即host.
For example, "src 10.1.1.1" is equivalent ro "src host 10.1.1.1".
Logical Operations：
(1)AND
and or &&
(2)OR
or or ||
(3)EXCEPT
not or !
参数说明：
-i any：Listen on all interfaces just to see if you're seeing any traffic.(指定接口)
-n：Don't resolve hostnames.(不反解主机名)
-nn：Don't resolve hostnames or port name.(不反解主机名，也不反解端口号对应的服务名)
-X：Show the packets's contents in both hex and ASCII.(把报文内容转为ASCII方式显示)
-XX：Same as -X,but also shows the ethernet header.(包含-X，同时会显示以太网帧首部信息)
-v,-vv,-vvv：Increase the amount of packet information you get back.(显示详细信息)
-c #：Only get x number of packets and then stop.(制定抓包的个数)
-s：Define the snaplength(size) of the capture in bytes. Use -s0 to get everything,unless you are intentionally capturing less.()
-S：Print absolute sequence numbers.(显示报文的序列号)
-e：Get the ethernet header as well.(显示以太网首部信息)
-q：Show less protocol information.(显示更少的协议信息)
-E：Decrypt IPSEC traffic by providing an encryption key.(通过提供一个加密密钥解密IPSEC传输信息)
-A：Display Cpatured Packets in ASCII.(把报文内容转为ASCII方式显示)
-w /path/from/some_file：Capture the packets from a saved file.(捕获的数据包保存文件)
-r /path/from/some_file：Reading the packets from a saved file.(读取捕获的数据包文件信息)
-tttt：Capture packets with proper readable timestamp.(捕获数据包通过适当的可读的时间戳)
例子：
抓取eht1的所有报文信息，并以
tcpdump -i eth1 -nn -XX ip dst host 192.168.2.2 and tcp dst port 3306