抓eth1的包
tcpdump -i eth1 -w /tmp/xxx.cap
抓 192.168.1.123的包
tcpdump -i eth1 host 192.168.1.123 -w /tmp/xxx.cap
抓192.168.1.123的80端口的包
tcpdump -i eth1 host 192.168.1.123 and port 80 -w /tmp/xxx.cap
抓192.168.1.123的icmp的包
tcpdump -i eth1 host 192.168.1.123 and icmp -w /tmp/xxx.cap
抓192.168.1.123的80端口和110和25以外的其他端口的包
tcpdump -i eth1 host 192.168.1.123 and ! port 80 and ! port 25 and ! port 110 -w /tmp/xxx.cap
抓vlan 1的包
tcpdump -i eth1 port 80 and vlan 1 -w /tmp/xxx.cap
抓pppoe的密码
tcpdump -i eth1 pppoes -w /tmp/xxx.cap
以100m大小分割保存文件， 超过100m另开一个文件
-C 100m
抓10000个包后退出
-c 10000
后台抓包， 控制台退出也不会影响：
nohup tcpdump -i eth1 port 110 -w /tmp/xxx.cap &
抓下来的文件可以直接用ethereal 或者wireshark打开。