What is nc under centos

NC under centos is the abbreviation of "netcat". It is a network tool that can be used for port scanning, file transfer, etc. nc can also implement listening on any TCP and UDP ports. You can use "yum install nc -y" command to install.

The operating environment of this article: centos 7 system, Dell G3 computer.

What is nc under centos

nc is the abbreviation of netcat tool, a network tool that can be used for port scanning, file transfer and other functions.

The installation on centos is also very simple:

yum install nc -y

nc commonly used functions

• realize any TCP /UDP port listening, nc can act as a server to listen to the specified port in TCP or UDP mode

• Port scanning, nc can act as a client to initiate a TCP or UDP connection

• Transfer files between machines

• Network speed test between machines

Generally nc is only used for TCP/UDP Protocol port testing, other functions should be used sparingly!

nc Help Description

# 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 <command>    Executes the given command via /bin/sh
  -e, --exec <command>       Executes the given command
      --lua-exec <filename>  Executes the given Lua script
  -g hop1[,hop2,...]         Loose source routing hop points (8 max)
  -G <n>                     Loose source routing hop pointer (4, 8, 12, ...)
  -m, --max-conns <n>        Maximum <n> simultaneous connections
  -h, --help                 Display this help screen
  -d, --delay <time>         Wait between read/writes
  -o, --output <filename>    Dump session data to a file
  -x, --hex-dump <filename>  Dump session data as hex to a file
  -i, --idle-timeout <time>  Idle read/write timeout
  -p, --source-port port     Specify source port to use
  -s, --source addr          Specify source address to use (doesn&#39;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 <time>          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&#39;s connection brokering mode
      --chat                 Start a simple Ncat chat server
      --proxy <addr[:port]>  Specify address of host to proxy through
      --proxy-type <type>    Specify proxy type ("http" or "socks4" or "socks5")
      --proxy-auth <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&#39;s version information and exit

nc Common Cases

TCP Listening Test

nc can be used as the server side 192.168.10.11 to start a tcp monitoring

nc -l 80

Client test method: directly telnet the machine ip port

telnet 192.168.10.11 80

Or: nmap 192.168.10.11 -p 80

UDP listening test

nc starts a udp as the server Monitoring

nc -lu 80

You can see through netstat that the udp protocol has been monitored:

> # 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

Recommended tutorial: "centos tutorial"

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