本文操作环境：centos 7系统、Dell G3电脑。

centos下什么是nc

nc是netcat工具的简称，一个网络工具，可以用来端口扫描、文件传输等功能。

centos上面安装也很简单：

yum install nc -y

nc常用功能

• 实现任意TCP/UDP端口的侦听，nc可以作为server以TCP或UDP方式侦听指定端口

• 端口的扫描，nc可以作为client发起TCP或UDP连接

• 机器之间传输文件

• 机器之间网络测速

一般nc只用来做TCP/UDP协议的端口测试，其它功能少用！

nc帮助说明

# nc --help 
Ncat 7.50 ( https://nmap.org/ncat )
Usage: ncat [options] [hostname] [port]
Options taking a time assume seconds. Append 'ms' for milliseconds,
's' for seconds, 'm' for minutes, or 'h' for hours (e.g. 500ms).
  -4                         Use IPv4 only
  -6                         Use IPv6 only
  -U, --unixsock             Use Unix domain sockets only
  -C, --crlf                 Use CRLF for EOL sequence
  -c, --sh-exec     Executes the given command via /bin/sh
  -e, --exec        Executes the given command
      --lua-exec   Executes the given Lua script
  -g hop1[,hop2,...]         Loose source routing hop points (8 max)
  -G                      Loose source routing hop pointer (4, 8, 12, ...)
  -m, --max-conns         Maximum  simultaneous connections
  -h, --help                 Display this help screen
  -d, --delay          Wait between read/writes
  -o, --output     Dump session data to a file
  -x, --hex-dump   Dump session data as hex to a file
  -i, --idle-timeout   Idle read/write timeout
  -p, --source-port port     Specify source port to use
  -s, --source addr          Specify source address to use (doesn't affect -l)
  -l, --listen               Bind and listen for incoming connections
  -k, --keep-open            Accept multiple connections in listen mode
  -n, --nodns                Do not resolve hostnames via DNS
  -t, --telnet               Answer Telnet negotiations
  -u, --udp                  Use UDP instead of default TCP
      --sctp                 Use SCTP instead of default TCP
  -v, --verbose              Set verbosity level (can be used several times)
  -w, --wait           Connect timeout
  -z                         Zero-I/O mode, report connection status only
      --append-output        Append rather than clobber specified output files
      --send-only            Only send data, ignoring received; quit on EOF
      --recv-only            Only receive data, never send anything
      --allow                Allow only given hosts to connect to Ncat
      --allowfile            A file of hosts allowed to connect to Ncat
      --deny                 Deny given hosts from connecting to Ncat
      --denyfile             A file of hosts denied from connecting to Ncat
      --broker               Enable Ncat's connection brokering mode
      --chat                 Start a simple Ncat chat server
      --proxy   Specify address of host to proxy through
      --proxy-type     Specify proxy type ("http" or "socks4" or "socks5")
      --proxy-auth     Authenticate with HTTP or SOCKS proxy server
      --ssl                  Connect or listen with SSL
      --ssl-cert             Specify SSL certificate file (PEM) for listening
      --ssl-key              Specify SSL private key (PEM) for listening
      --ssl-verify           Verify trust and domain name of certificates
      --ssl-trustfile        PEM file containing trusted SSL certificates
      --ssl-ciphers          Cipherlist containing SSL ciphers to use
      --version              Display Ncat's version information and exit

nc常用案例

TCP监听测试

nc可作为server端192.168.10.11启动一个tcp的监听

nc -l 80

客户端测试方法：直接telnet该机器ip+端口

telnet 192.168.10.11 80

或：nmap 192.168.10.11 -p 80

UDP监听测试

nc作为server端启动一个udp的监听

nc -lu 80

通过netstat可以看到udp协议已经监听：

> # netstat -tunlp
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address   Foreign Address   State  PID/Program name   
udp        0      0 0.0.0.0:80      0.0.0.0:*                15401/nc

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