tcpdump抓包以及port查看的一些操作

1.tcpdump。

nginx开启后会占用80端口，此时运行命令：tcpdump tcp port 80

结果例如以下：

[syswj@host ~]$ sudo tcpdump tcp port 80
[sudo] password for syswj:
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on Auto_eth0, link-type EN10MB (Ethernet), capture size 65535 bytes

採用tcpdump抓到大包会显示到屏幕上：

1.在windows上通过telnet ip port号 来连接linux上80port执行的nginxserver

tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on Auto_eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
14:14:23.406697 IP 192.168.137.1.7352 > 192.168.137.128.http: Flags [S], seq 322176964, win 8192, options [mss 1460,nop,wscale 8,nop,nop,sackOK], length 0
14:14:23.406740 IP 192.168.137.128.http > 192.168.137.1.7352: Flags [S.], seq 300095102, ack 322176965, win 14600, options [mss 1460,nop,nop,sackOK,nop,wscale 6], length 0
14:14:23.406992 IP 192.168.137.1.7352 > 192.168.137.128.http: Flags [.], ack 1, win 256, length 0

这就是tcp的3次握手经过

2.退出windows上的telnet后：

14:16:37.910069 IP 192.168.137.1.7360 > 192.168.137.128.http: Flags [F.], seq 1, ack 1, win 256, length 0
14:16:37.910194 IP 192.168.137.128.http > 192.168.137.1.7360: Flags [F.], seq 1, ack 2, win 229, length 0
14:16:37.910854 IP 192.168.137.1.7360 > 192.168.137.128.http: Flags [.], ack 2, win 256, length 0

client跟server发送一个FIN结束报文，server收到后。

3.在网页上(windows)进入http:192.168.137.128

进入的时候：

[sudo] password for syswj:
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on Auto_eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
14:23:09.504575 IP 192.168.137.1.rtps-dd-mt > 192.168.137.128.http: Flags [S], seq 4063271087, win 65535, options [mss 1460,nop,wscale 8,nop,nop,sackOK], length 0
14:23:09.504610 IP 192.168.137.128.http > 192.168.137.1.rtps-dd-mt: Flags [S.], seq 1526809447, ack 4063271088, win 14600, options [mss 1460,nop,nop,sackOK,nop,wscale 6], length 0
14:23:09.504867 IP 192.168.137.1.rtps-dd-mt > 192.168.137.128.http: Flags [.], ack 1, win 1024, length 0

也是和上面一样的3次握手

关闭页面，等待一段时间后：

14:24:09.565990 IP 192.168.137.128.http > 192.168.137.1.rtps-dd-mt: Flags [F.], seq 1, ack 1, win 229, length 0
14:24:09.566290 IP 192.168.137.1.rtps-dd-mt > 192.168.137.128.http: Flags [.], ack 2, win 1024, length 0

再等待一段时间后：

14:25:32.242143 IP 192.168.137.1.rtps-dd-mt > 192.168.137.128.http: Flags [F.], seq 1, ack 2, win 1024, length 0
14:25:32.242248 IP 192.168.137.128.http > 192.168.137.1.rtps-dd-mt: Flags [R], seq 1526809449, win 0, length 0

--由于超时的原因server已经关闭了这个连接，此时client再向server发送信息，server根本不识别这个client，所以返回一个RST报文

关于port的一些命令：

lsof -i :port号 ----查看port进程信息

关闭某个port的进程：

先用lsof -i:port号 查出这个port的进程，找出pid，然后kill -9 pid。关闭进程

或者 直接: fuser -k 80/tcp

查看port进程：

netstat -anp | grep 80