网络命令-nc(一)

一直在linux环境下编程,但却没有用过nc命令,不过最近发现Netcat这个命令-nc,发现真的蛮强大的,

为了备忘,就写了这个博客吧,不求全,只求把自己觉得很有用的命令整理出来,这篇文章估计要长期更新,想到了,看到了好的用法就

更新一番吧。

 

先把man nc 的内容贴一下!

 

NC(1) NC(1)

NAME
nc - TCP/IP swiss army knife //看看吧,瑞士军刀

SYNOPSIS
nc [-options] hostname port[s] [ports] ...
nc -l -p port [-options] [hostname] [port]

 

DESCRIPTION
netcat is a simple unix utility which reads and writes data across network connections, using TCP or UDP protocol. It is designed to be a reliable "back-end" tool that can be
used directly or easily driven by other programs and scripts. At the same time, it is a feature-rich network debugging and exploration tool, since it can create almost any kind
of connection you would need and has several interesting built-in capabilities. Netcat, or "nc" as the actual program is named, should have been supplied long ago as another
one of those cryptic but standard Unix tools.

 

//nc命令的选项,研究nc命令也就是研究他的选项组合
OPTIONS
-c string specify shell commands to exec after connect (use with caution). The string is passed to /bin/sh -c for execution. See the -e option if you don't have a working
/bin/sh (Note that POSIX-conformant system must have one).

-e filename specify filename to exec after connect (use with caution). See the -c option for enhanced functionality.

-g gateway source-routing hop point[s], up to 8

-G num source-routing pointer: 4, 8, 12, ...

-h display help

-i secs delay interval for lines sent, ports scanned

-l listen mode, for inbound connects

-n numeric-only IP addresses, no DNS

-o file hex dump of traffic

-p port local port number (port numbers can be individual or ranges: lo-hi [inclusive])  指定监听的端口()

-q seconds after EOF on stdin, wait the specified number of seconds and then quit. If seconds is negative, wait forever.

-b allow UDP broadcasts

-r randomize local and remote ports

-s addr local source address

-t enable telnet negotiation

-u UDP mode  若使用UDP协议传输,使用此选项

-v verbose [use twice to be more verbose]

-w secs timeout for connects and final net reads

-z zero-I/O mode [used for scanning]

-T type set TOS flag (type may be one of "Minimize-Delay", "Maximize-Throughput", "Maximize-Reliability", or "Minimize-Cost".)

 

1:监听指定端口

监听本地端口

nc -l 12345 ,如果你要将监听的输入指定到指定的文件,比如/dev/zero

nc -l 12345 > /dev/null

 

2:向指定主机的某一端口发送连接

nc  www.example.com 12345 (向www.example.com 主机的12345 端口建立tcp连接)

 

3:若想使用UDP连接,则两端都要使用-u 选项

 

4: -v 选项,显示nc 输出内容

例如 nc -l-v 12345 > /dev/null

输出:

root@ubuntu:~# nc -l -v -p 12345 > /dev/null
Listening on [0.0.0.0] (family 0, port 12345)

 

nc localhost -v 12345

输出:

root@ubuntu:~# nc -v localhost 12345
Connection to localhost 12345 port [tcp/*] succeeded!

5:可以使用nc 命令,-z选项扫描某一主机的端口是否开放

例如:检测我本机的10-30端口有哪些是开放的

nc -v -z localhost 10-30 

 

可以看到,我本机的13,21,22端口是开放的,而其他的端口都是关闭的

所以估计黑客门喜欢用吧,不过也许人家用更高达上的工具吧。不过对来我说很好用

 

6:使用 -w 选项限定空闲时间

服务端,可以使用 -w 选项来设置空闲时间限制。也就是说,当连接空闲超时时,连接会自动断开。注意,-w 选项并不会影响 -l 选项,也就是说,

如果还没有连接进来时,即使超出了超时时间,那么服务端的监听并不会自动断开。这里的超时是相对于连接来说的。比如下面服务端的设定

7:进行代理

比如我使用如下命令

nc -v -l 8899 | nc -v www.sina.com.cn 80

上面的意思是,先使 nc 监听在 8899 端口。如果客户端访问服务器的 8899 端口,那么就将请求通过管道送到另一边的 nc 命令中,该 nc 命令再将请求内容发往  www.sina.com.cn ,

当 www.sina.com.cn 响应时,所返回网站内容默认输出到标准输出上(文件描述符为 1),此时我们将这些内容重定向到 tunnel 这个有名管道中,一旦管道有了内容,它就输送到标准输入(0),

接着标准输入的内容被左端的 nc 接收,最后 nc 就将这些内容返回到客户端去

 

好了,有机会继续总结。。。。

posted @ 2015-05-11 00:09  Geeking  阅读(1094)  评论(0编辑  收藏  举报