一，iftop的作用:
基于ip统计外部机器与本机之间的网络流量，
可以方便的查看各客户端是否有非正常的到本机的访问
说明：刘宏缔的架构森林是一个专注架构的博客，地址：https://www.cnblogs.com/architectforest
对应的源码可以访问这里获取： https://github.com/liuhongdi/
说明：作者:刘宏缔 邮箱: 371125307@qq.com
二，安装iftop:
[root@yjweb ~]# yum install iftop
说明：如果yum报错没有任何匹配,则先安装epel源
[root@localhost liuhongdi]# yum install epel-release
三，查看iftop的帮助信息与版本
[root@yjweb ~]# iftop -h
iftop: display bandwidth usage on an interface by host
Synopsis: iftop -h | [-npblNBP] [-i interface] [-f filter code]
[-F net/mask] [-G net6/mask6]
-h display this message
-n don't do hostname lookups
-N don't convert port numbers to services
-p run in promiscuous mode (show traffic between other
hosts on the same network segment)
-b don't display a bar graph of traffic
-B display bandwidth in bytes
-a display bandwidth in packets
-i interface listen on named interface
-f filter code use filter code to select packets to count
(default: none, but only IP packets are counted)
-F net/mask show traffic flows in/out of IPv4 network
-G net6/mask6 show traffic flows in/out of IPv6 network
-l display and count link-local IPv6 traffic (default: off)
-P show ports as well as hosts
-m limit sets the upper limit for the bandwidth scale
-c config file specifies an alternative configuration file
-t use text interface without ncurses Sorting orders:
-o 2s Sort by first column (2s traffic average)
-o 10s Sort by second column (10s traffic average) [default]
-o 40s Sort by third column (40s traffic average)
-o source Sort by source address
-o destination Sort by destination address The following options are only available in combination with -t
-s num print one single text output afer num seconds, then quit
-L num number of lines to print iftop, version 1.0pre4
copyright (c) 2002 Paul Warren <pdw@ex-parrot.com> and contributors
四，iftop最常用的三个参数
[root@loadserver ~]# iftop -n -N -P
-n:使host信息默认直接都显示IP
（默认会反解成域名，没必要）
-N:使端口信息默认直接都显示端口号
(默认会显示成服务，如:http,https,
没必要，自定义的端口也显示不了)
-P:使host信息及端口信息默认就都显示
说明：加了-P这个参数的统计是统计到了端口，
如果只想看统计到主机，则去掉-P参数
五，iftop的常用方法举例：
1，查看指定网卡的流量情况：
[root@loadserver ~]# iftop -n -N -P -i eth0
2，查看某个ip或网段的流量情况
[root@loadserver ~]# iftop -n -N -P -F 172.117.123.26/32
六，iftop的常用交互命令:
1，q:退出监控
2, b: 打开/关闭流量图形条
(一般不使用)
3,p: 打开/关闭按端口统计
4,P:暂停/继续显示
有时需要查看某一时间点的数据
5，T：打开/关闭 显示每个连接的总流量
6，h:打开/关闭 交互命令的帮助界面
七，把iftop的显示数据输出到文件
[root@loadserver ~]# iftop -t > /root/iftop.txt
八，查看当前的centos版本
[root@yjweb ~]# cat /etc/redhat-release
CentOS Linux release 8.0.1905 (Core)