以下将给出9个使用tcpdump的例子，以说明tcpdump的具体使用方法。
1.针对特定网口抓包(-i选项)
当我们不加任何选项执行tcpdump时，tcpdump将抓取通过所有网口的包；使用-i选项，我们可以在某个指定的网口抓包：
linux:/tmp/lx # tcpdump -i eth0 tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes 10:50:28.607429 IP 10.70.121.92.autodesk-lm > 10.71.171.140.ssh: . ack 116 win 64951 10:50:28.607436 IP 10.71.171.140.ssh > 10.70.121.92.autodesk-lm: P 116:232(116) ack 1 win 12864 10:50:30.384195 arp who-has 128.128.128.35 tell 128.128.128.35
以上例子中，tcpdump抓取所有通过eth0的包。
2.抓取指定数目的包(-c选项)
默认情况下tcpdump将一直抓包，直到按下”ctrl+c”中止，使用-c选项我们可以指定抓包的数量：
linux:/tmp/lx # tcpdump -c 2 -i eth0 tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes 10:58:05.656104 IP 10.71.171.140.ssh > 10.70.121.92.autodesk-lm: P 1210443473:1210443589(116) ack 2583117929 win 12864 10:58:05.657074 IP 10.70.121.92.autodesk-lm > 10.71.171.140.ssh: . ack 116 win 65211 2 packets captured 6 packets received by filter 0 packets dropped by kernel
以上例子中，只针对eth0网口抓2个包。
3.将抓到包写入文件中(-w选项)
使用-w选项，我们可将抓包记录到一个指定文件中，以供后续分析
linux:/tmp/lx # tcpdump -w 20120606.pcap -i eth0 tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes 75 packets captured 150 packets received by filter 0 packets dropped by kernel
应当保存为.pcap后缀的文件，方便我们使用wireshark等工具读取分析。
4.读取tcpdump保存文件(-r选项)
对于保存的抓包文件，我们可以使用-r选项进行读取：
linux:/tmp/lx # tcpdump -r 20120606.pcap reading from file 20120606.pcap, link-type EN10MB (Ethernet) 11:01:57.392907 IP 10.71.171.140.ssh > 10.70.121.92.autodesk-lm: P 1210446405:1210446457(52) ack 2583119957 win 12864 11:01:57.392917 IP 10.71.171.140.ssh > 10.70.121.92.autodesk-lm: P 52:168(116) ack 1 win 12864 11:01:57.393649 IP 10.70.121.92.autodesk-lm > 10.71.171.140.ssh: . ack 52 win 65327
5.抓包时不进行域名解析(-n选项)
默认情况下，tcpdump抓包结果中将进行域名解析，显示的是域名地址而非ip地址，使用-n选项，可指定显示ip地址。
6.增加抓包时间戳(-tttt选项)
使用-tttt选项，抓包结果中将包含抓包日期：
linux:/tmp/lx # tcpdump -n -tttt -i eth0 2012-06-06 11:14:59.539736 IP 10.71.171.140.22 > 10.70.121.95.1787: P 1:53(52) ack 100 win 7504 2012-06-06 11:14:59.539754 IP 10.71.171.140.22 > 10.70.121.95.1787: P 53:105(52) ack 100 win 7504 2012-06-06 11:14:59.539770 IP 10.71.171.140.22 > 10.70.121.95.1787: P 105:157(52) ack 100 win 7504
7.指定抓包的协议类型
我们可以只抓某种协议的包，tcpdump支持指定以下协议：ip,ip6,arp,tcp,udp,wlan等。以下例子只抓取arp协议的包：
linux:/tmp/lx # tcpdump -i eth0 arp tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes 11:22:26.948656 arp who-has 10.10.1.30 tell 10.10.1.26 11:22:27.017406 arp who-has 10.10.1.30 tell 10.10.1.26 11:22:27.078803 arp who-has 10.10.1.30 tell 10.10.1.26
8.指定抓包端口
如果想要对某个特定的端口抓包，可以通过以下命令：
linux:/tmp/lx # tcpdump -i eth0 port 22 tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes 11:41:04.387547 IP 10.70.121.92.autodesk-lm > 10.71.171.140.ssh: . ack 1216136825 win 64751 11:41:04.387891 IP 10.71.171.140.ssh > 10.70.121.92.autodesk-lm: P 1:233(232) ack 0 win 16080 11:41:04.398973 IP 10.70.121.92.autodesk-lm > 10.71.171.140.ssh: P 0:52(52) ack 233 win 64519
9.抓取特定目标ip和端口的包
网络包的内容中，包含了源ip地址、端口和目标ip、端口，我们可以根据目标ip和端口过滤tcpdump抓包结果，以下命令说明了此用法：
linux:/tmp/lx # tcpdump -i eth0 dst 10.70.121.92 and port 22
Reference: Packet Analyzer: 15 TCPDUMP Command Examples