Skip to content

Instantly share code, notes, and snippets.

Embed
What would you like to do?
This gist contains basic usage examples of netcat tool, a feature-rich network debugging and exploration tool.

Minimalist Netcat usage examples:

Connect to TCP port 80 on host example.com:

nc -vv <hostname> 80

Port scan TCP ports 7 through 1023 on a specified host:

nc -v -z <hostname> 7-1023

Port scan TCP ports 7 through 1023 on a specific host, but stop for user interaction on open ports

nc -v <hostname> 7-1023

Port scan UDP ports 53 through 69 on a given host:

nc -v -z -u <hostname> 53-69

Listen for inbound connections on TCP port 1234 and pipe the results to a file data.txt

nc -vv -l 1234 > data.txt

Listen for inbound connections on TCP port 25 and pipe the results to /dev/null

nc -vv -l 25 > /dev/null

Listen for inbound connections on TCP port 25 and pipe the results to /dev/null, but keep listening on the port even after a disconnect.

nc -vv -k -l 25 > /dev/null

Listen for inbound connections on TCP port 25, keep listening on the port open even after a disconnect, but automatically drop any session after 3 seconds of inactivity:

nc -vv -k -w 3 -l 25

Listen for inbound connections on TCP port 25, automatically pushing the contents of file welcome.txt upon a connection.

cat welcome.txt | nc -vv -l 25

Transfer contents of file payload.txt to a given hostname using TCP port 1234

nc -vv <hostname> 1234 < payload.txt

And then receive the contents of the file from the remote host on the target host:

nc -vv -k -l 1234 > payload.txt

Transfer the image of device /dev/sda1 to host example.com using TCP port 1234

dd if=/dev/sda1 | nc -vv <hostname> 1234

Receive the raw image file of the imaged partition from the remote host to the target host:

nc -vv -k -l 1234 > drive.img

Advanced nc arguments:

-4: Forces nc to use IPv4 addresses only.

-6: Forces nc to use IPv6 addresses only.

-b: Allow broadcast.

-C: Send CRLF as line-ending.

-D: Enable debugging on the socket.

-d: Do not attempt to read from stdin.

-h: Prints out nc help.

-I: length Specifies the size of the TCP receive buffer.

-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 connection 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.

-O: (length) Specifies the size of the TCP send buffer.

-P: (proxy_username) Specifies a username to present to a proxy server that requires authentication. If no username is specified then authentication will not be attempted. Proxy authentication is only supported for HTTP CONNECT proxies at present.

-p: Specifies the source port nc should use, subject to privilege restrictions and availability.

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

-r: Specifies that source and/or destination ports should be chosen randomly instead of sequentially within a range or in the order that the system assigns them.

-S: Enables the RFC 2385 TCP MD5 signature option.

-s: (source) Specifies the IP of the interface which is used to send the packets. For UNIX-domain datagram sockets, specifies the local temporary socket file to create and use so that datagrams can be received. It is an error to use this option in conjunction with the -l option.

-T (toskeyword): Change IPv4 TOS value. toskeyword may be one of critical, inetcontrol, lowcost, lowdelay, netcontrol, throughput, reliability, or one of the DiffServ Code Points: ef, af11 ... af43, cs0 ... cs7; or a number in either hex or decimal.

-t: Causes nc to send RFC 854 DON'T and WON'T 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. For UNIX-domain sockets, use a datagram socket instead of a stream socket. If a UNIX-domain socket is used, a temporary receiving socket is created in /tmp unless the -s flag is given.

-V: (rtable) Set the routing table to be used. The default is 0.

-v: Have nc give more verbose output.

-w: (timeout) Connections which cannot be established or are idle timeout after timeout seconds. 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_protocol) Requests that nc should use the specified protocol when talking to the proxy server. Supported 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 destination 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: Enables DCCP mode.

-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.

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
You can’t perform that action at this time.