即NetCat简写，在网络工具中有“瑞士军刀”美誉，其有Windows和Linux的版本。因为它短小精悍（1.84版本也不过25k，旧版本或缩减版甚至更小）、功能实用，被设计为一个简单、可靠的网络工具，可通过TCP或UDP协议传输读写数据。同时，它还是一个网络应用Debug分析器，因为它可以根据需要创建各种不同类型的网络连接。NetCat 官方地址：

功能说明：功能强大的网络工具语　　法：nc [-hlnruz][-g
     <网关...>
      ][-G
      <指向器数目>
       ][-i
       <延迟秒数>
        ][-o
        <输出文件>
         ][-p
         <通信端口>
          ][-s
          <来源位址>
           ][-v...][-w
           <超时秒数>
            ][主机名称][通信端口...]参　　数： -g 
            <网关>
              设置路由器跃程通信网关，最多可设置8个。 -G 
             <指向器数目>
               设置来源路由指向器，其数值为4的倍数。 -h 在线帮助。 -i 
              <延迟秒数>
                设置时间间隔，以便传送信息及扫描通信端口。 -l 使用监听模式，管控传入的资料。 -n 直接使用IP地址，而不通过域名服务器。 -o 
               <输出文件>
                 指定文件名称，把往来传输的数据以16进制字码倾倒成该文件保存。 -p 
                <通信端口>
                  设置本地主机使用的通信端口。 -r 乱数指定本地与远端主机的通信端口。 -s 
                 <来源位址>
                   设置本地主机送出数据包的IP地址。 -u 使用UDP传输协议。 -v 显示指令执行过程。 -w 
                  <超时秒数>
                    设置等待连线的时间。 -z 使用0输入/输出模式，只在扫描通信端口时使用。
                  
                 
                
               
              
             
            
           
          
         
        
       
      
     

1.端口扫描

[root@rusky2 ~]# nc -v  192.168.2.100 -z 11162-11170Connection to 192.168.2.100 11162 port [tcp/suncacao-jmxmp] succeeded!Connection to 192.168.2.100 11163 port [tcp/suncacao-rmi] succeeded!Connection to 192.168.2.100 11164 port [tcp/suncacao-csa] succeeded!nc: connect to 192.168.2.100 port 11165 (tcp) failed: Connection refusednc: connect to 192.168.2.100 port 11166 (tcp) failed: Connection refusednc: connect to 192.168.2.100 port 11167 (tcp) failed: Connection refusednc: connect to 192.168.2.100 port 11168 (tcp) failed: Connection refusednc: connect to 192.168.2.100 port 11169 (tcp) failed: Connection refusednc: connect to 192.168.2.100 port 11170 (tcp) failed: Connection refused

不加-v参数，则只显示已打开的端口

[root@rusky2 ~]# nc   192.168.2.100 -z 11162-11170Connection to 192.168.2.100 11162 port [tcp/suncacao-jmxmp] succeeded!Connection to 192.168.2.100 11163 port [tcp/suncacao-rmi] succeeded!Connection to 192.168.2.100 11164 port [tcp/suncacao-csa] succeeded!

2、简单聊天工具

[root@rusky ~]# nc -l 1234   #rusky开始端口1234hello ruskyhello rusky2[root@rusky2 ~]# nc 192.168.2.100 1234 　　#rusk2连接端口1234hello ruskyhello rusky2

   [root@rusky ~]# netstat -an | grep 1234

   tcp 0 0 0.0.0.0:1234 0.0.0.0:* LISTEN

   tcp 0 0 192.168.2.100:1234 192.168.2.200:58039 ESTABLISHED

3.。。。。。。。。　　　　　　

[root@YncmIAM-ESP-a ~]# man 1 ncNC(1)                     BSD General Commands Manual                    NC(1)NAME     nc - arbitrary TCP and UDP connections and listensSYNOPSIS     nc [-46DdhklnrStUuvz] [-i interval] [-p source_port] [-s source_ip_address] [-T ToS] [-w timeout]        [-X proxy_protocol] [-x proxy_address[:port]] [hostname] [port[s]]DESCRIPTION     The nc (or netcat) utility is used for just about anything under the sun involving TCP or UDP.  It can     open TCP connections, send UDP packets, listen on arbitrary TCP and UDP ports, do port scanning, and     deal with both IPv4 and IPv6.  Unlike telnet(1), nc scripts nicely, and separates error messages onto     standard error instead of sending them to standard output, as telnet(1) does with some.     Common uses include:           ??¤   simple TCP proxies           ??¤   shell-script based HTTP clients and servers           ??¤   network daemon testing           ??¤   a SOCKS or HTTP ProxyCommand for ssh(1)           ??¤   and much, much more     The options are as follows:     -4      Forces nc to use IPv4 addresses only.     -6      Forces nc to use IPv6 addresses only.     -D      Enable debugging on the socket.     -d      Do not attempt to read from stdin.     -h      Prints out nc help.     -i interval             Specifies a delay time interval between lines of text sent and received.  Also causes a delay             time between connections to multiple ports.     -k      Forces nc to stay listening for another connection after its current connection is completed.             It is an error to use this option without the -l option.     -l      Used to specify that nc should listen for an incoming connection rather than initiate a con-             nection to a remote host.  It is an error to use this option in conjunction with the -p, -s,             or -z options.  Additionally, any timeouts specified with the -w option are ignored.     -n      Do not do any DNS or service lookups on any specified addresses, hostnames or ports.     -p source_port             Specifies the source port nc should use, subject to privilege restrictions and availability.             It is an error to use this option in conjunction with the -l option.     -r      Specifies that source and/or destination ports should be chosen randomly instead of sequen-             tially within a range or in the order that the system assigns them.     -S      Enables the RFC 2385 TCP MD5 signature option.     -s source_ip_address             Specifies the IP of the interface which is used to send the packets.  It is an error to use             this option in conjunction with the -l option.     -T ToS  Specifies IP Type of Service (ToS) for the connection.  Valid values are the tokens             ?°lowdelay?±, ?°throughput?±, ?°reliability?±, or an 8-bit hexadecimal value preceded by ?°0x?±.     -t      Causes nc to send RFC 854 DON?ˉT and WON?ˉT responses to RFC 854 DO and WILL requests.  This             makes it possible to use nc to script telnet sessions.     -U      Specifies to use Unix Domain Sockets.     -u      Use UDP instead of the default option of TCP.     -v      Have nc give more verbose output.     -w timeout             If a connection and stdin are idle for more than timeout seconds, then the connection is             silently closed.  The -w flag has no effect on the -l option, i.e. nc will listen forever for             a connection, with or without the -w flag.  The default is no timeout.     -X proxy_version             Requests that nc should use the specified protocol when talking to the proxy server.  Sup-             ported protocols are ?°4?± (SOCKS v.4), ?°5?± (SOCKS v.5) and ?°connect?± (HTTPS proxy).  If the             protocol is not specified, SOCKS version 5 is used.     -x proxy_address[:port]             Requests that nc should connect to hostname using a proxy at proxy_address and port.  If port             is not specified, the well-known port for the proxy protocol is used (1080 for SOCKS, 3128 for             HTTPS).     -z      Specifies that nc should just scan for listening daemons, without sending any data to them.             It is an error to use this option in conjunction with the -l option.     hostname can be a numerical IP address or a symbolic hostname (unless the -n option is given).  In     general, a hostname must be specified, unless the -l option is given (in which case the local host is     used).     port[s] can be single integers or ranges.  Ranges are in the form nn-mm.  In general, a destination     port must be specified, unless the -U option is given (in which case a socket must be specified).CLIENT/SERVER MODEL     It is quite simple to build a very basic client/server model using nc.  On one console, start nc lis-     tening on a specific port for a connection.  For example:           $ nc -l 1234     nc is now listening on port 1234 for a connection.  On a second console (or a second machine), connect     to the machine and port being listened on:           $ nc 127.0.0.1 1234     There should now be a connection between the ports.  Anything typed at the second console will be con-     catenated to the first, and vice-versa.  After the connection has been set up, nc does not really care     which side is being used as a ??server?ˉ and which side is being used as a ??client?ˉ.  The connection may     be terminated using an EOF (??^D?ˉ).DATA TRANSFER     The example in the previous section can be expanded to build a basic data transfer model.  Any infor-     mation input into one end of the connection will be output to the other end, and input and output can     be easily captured in order to emulate file transfer.     Start by using nc to listen on a specific port, with output captured into a file:           $ nc -l 1234 > filename.out     Using a second machine, connect to the listening nc process, feeding it the file which is to be trans-     ferred:           $ nc host.example.com 1234 < filename.in     After the file has been transferred, the connection will close automatically.TALKING TO SERVERS     It is sometimes useful to talk to servers ?°by hand?± rather than through a user interface.  It can aid     in troubleshooting, when it might be necessary to verify what data a server is sending in response to     commands issued by the client.  For example, to retrieve the home page of a web site:           $ echo -n "GET / HTTP/1.0\r\n\r\n" | nc host.example.com 80     Note that this also displays the headers sent by the web server.  They can be filtered, using a tool     such as sed(1), if necessary.     More complicated examples can be built up when the user knows the format of requests required by the     server.  As another example, an email may be submitted to an SMTP server using:           $ nc localhost 25 << EOF           HELO host.example.com           MAIL FROM: 
     
                 RCPT TO: 
      
                  DATA           Body of email.           .           QUIT           EOFPORT SCANNING     It may be useful to know which ports are open and running services on a target machine.  The -z flag     can be used to tell nc to report open ports, rather than initiate a connection.  For example:           $ nc -z host.example.com 20-30           Connection to host.example.com 22 port [tcp/ssh] succeeded!           Connection to host.example.com 25 port [tcp/smtp] succeeded!     The port range was specified to limit the search to ports 20 - 30.     Alternatively, it might be useful to know which server software is running, and which versions.  This     information is often contained within the greeting banners.  In order to retrieve these, it is neces-     sary to first make a connection, and then break the connection when the banner has been retrieved.     This can be accomplished by specifying a small timeout with the -w flag, or perhaps by issuing a     "QUIT" command to the server:           $ echo "QUIT" | nc host.example.com 20-30           SSH-1.99-OpenSSH_3.6.1p2           Protocol mismatch.           220 host.example.com IMS SMTP Receiver Version 0.84 ReadyEXAMPLES     Open a TCP connection to port 42 of host.example.com, using port 31337 as the source port, with a     timeout of 5 seconds:           $ nc -p 31337 -w 5 host.example.com 42     Open a UDP connection to port 53 of host.example.com:           $ nc -u host.example.com 53     Open a TCP connection to port 42 of host.example.com using 10.1.2.3 as the IP for the local end of the     connection:           $ nc -s 10.1.2.3 host.example.com 42     Create and listen on a Unix Domain Socket:           $ nc -lU /var/tmp/dsocket     Connect to port 42 of host.example.com via an HTTP proxy at 10.2.3.4, port 8080.  This example could     also be used by ssh(1); see the ProxyCommand directive in ssh_config(5) for more information.           $ nc -x10.2.3.4:8080 -Xconnect host.example.com 42SEE ALSO     cat(1), ssh(1)AUTHORS     Original implementation by *Hobbit* ?′hobbit@avian.org?μ.     Rewritten with IPv6 support by Eric Jackson ?′ericj@monkey.org?μ.CAVEATS     UDP port scans will always succeed (i.e. report the port as open), rendering the -uz combination of     flags relatively useless.BSD