在baidu和google上找了N篇文章，都没有一篇是介绍怎么用iftop的-f参数，全部都是说“-f这个暂时还不太会用，过滤计算包用的”，最后，终于找到了使用方法，介绍如下：
iftop accepts pcap-filter formatted filters on the commandline with the -f flag. Below is a table of some of the filers you might want to use with iftop:
| dst host host | src host host |
| dst net net | src net net |
| dst port port | src port port |
| dst portrange start-end | src portrange start-end |
| gateway gateway | |
| ip proto protocol |
For example, to view only traffic going from your local machine to www.itkylin.com over eth0, you could run:
iftop -i eth0 -f “dst host www.itkylin.com”
Or to see only ssh traffic over wlan0:
iftop -i wlan0 -f “dst port 22″
其它的使用方法自己上baidu或google上找吧，此处不做重复介绍了！