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version 1.27, 2004/01/22 13:28:46 version 1.28, 2004/02/20 10:53:10
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 .Os  .Os
 .Sh NAME  .Sh NAME
 .Nm nc  .Nm nc
 .Nd "arbitrary TCP and UDP connections and listens"  .Nd arbitrary TCP and UDP connections and listens
 .Sh SYNOPSIS  .Sh SYNOPSIS
 .Nm nc  .Nm nc
 .Op Fl 46hklnrtuvzSU  .Op Fl 46hklnrStUuvz
 .Op Fl i Ar interval  .Op Fl i Ar interval
 .Op Fl p Ar source port  .Op Fl p Ar source_port
 .Op Fl s Ar source ip address  .Op Fl s Ar source_ip_address
 .Op Fl x Ar proxy address Op :port  
 .Op Fl w Ar timeout  .Op Fl w Ar timeout
 .Op Fl X Ar socks version  .Op Fl X Ar socks_version
   .Oo Xo
   .Fl x Ar proxy_address Ns Oo : Ns
   .Ar port Oc Oc
   .Xc
 .Op Ar hostname  .Op Ar hostname
 .Op Ar port[s]  .Op Ar port Ns Bq Ar s
 .Sh DESCRIPTION  .Sh DESCRIPTION
 The  The
 .Nm  .Nm
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 .It  .It
 simple TCP proxies  simple TCP proxies
 .It  .It
 shell\-script based HTTP clients and servers  shell-script based HTTP clients and servers
 .It  .It
 network daemon testing  network daemon testing
 .It  .It
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 .Nm  .Nm
 to stay listening for another connection after its current connection  to stay listening for another connection after its current connection
 is completed.  is completed.
   It is an error to use this option without the
   .Fl l
   option.
 .It Fl l  .It Fl l
 Used to specify that  Used to specify that
 .Nm  .Nm
 should listen for an incoming connection rather than initiate a  should listen for an incoming connection rather than initiate a
 connection to a remote host.  connection to a remote host.
   It is an error to use this option in conjunction with the
   .Fl p ,
   .Fl s ,
   or
   .Fl z
   options.
 .It Fl n  .It Fl n
 Do not do any DNS or service lookups on any specified addresses,  Do not do any DNS or service lookups on any specified addresses,
 hostnames or ports.  hostnames or ports.
 .It Fl p Ar port  .It Fl p Ar source_port
 Specifies the source port  Specifies the source port
 .Nm  .Nm
 should use, subject to privilege restrictions and availability.  should use, subject to privilege restrictions and availability.
   It is an error to use this option in conjunction with the
   .Fl l
   option.
 .It Fl r  .It Fl r
 Specifies that source and/or destination ports should be chosen randomly  Specifies that source and/or destination ports should be chosen randomly
 instead of sequentially within a range or in the order that the system  instead of sequentially within a range or in the order that the system
 assigns them.  assigns them.
 .It Fl s Ar hostname/ip address  .It Fl S
   Enables the RFC 2385 TCP MD5 signature option.
   .It Fl s Ar source_ip_address
 Specifies the IP of the interface which is used to send the packets.  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
   .Fl l
   option.
 .It Fl t  .It Fl t
 Causes  Causes
 .Nm  .Nm
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 This makes it possible to use  This makes it possible to use
 .Nm  .Nm
 to script telnet sessions.  to script telnet sessions.
   .It Fl U
   Specifies to use Unix Domain Sockets.
 .It Fl u  .It Fl u
 Use UDP instead of the default option of TCP.  Use UDP instead of the default option of TCP.
 .It Fl v  .It Fl v
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 .Fl w  .Fl w
 flag.  flag.
 The default is no timeout.  The default is no timeout.
 .It Fl x Ar proxy address Op :port  .It Fl X Ar socks_version
 Requests that  Requests that
 .Nm  .Nm
   should use the specified version of the SOCKS protocol when talking to
   a SOCKS proxy.
   SOCKS versions 4 and 5 are currently supported.
   If the version is not specified, SOCKS version 5 is used.
   .It Xo
   .Fl x Ar proxy_address Ns Oo : Ns
   .Ar port Oc
   .Xc
   Requests that
   .Nm
 should connect to  should connect to
 .Ar hostname  .Ar hostname
 using a SOCKS proxy at address and port.  using a SOCKS proxy at
 If port is not specified, port 1080 is used.  .Ar proxy_address
   and
   .Ar port .
   If
   .Ar port
   is not specified, port 1080 is used.
 .It Fl z  .It Fl z
 Specifies that  Specifies that
 .Nm  .Nm
 should just scan for listening daemons, without sending any data to them.  should just scan for listening daemons, without sending any data to them.
 .It Fl S  It is an error to use this option in conjunction with the
 Enables the RFC 2385 TCP MD5 signature option.  .Fl l
 .It Fl U  option.
 Specifies to use Unix Domain Sockets.  
 .It Fl X Ar version  
 Requests that  
 .Nm  
 should use the specified version of the SOCKS protocol when talking to  
 a SOCKS proxy.  
 If version is not specified, SOCKS version 5 is used.  
 .El  .El
   .Sh CLIENT/SERVER MODEL
   It is quite simple to build a very basic client/server model using
   .Nm .
   On one console, start
   .Nm
   listening on a specific port for a connection.
   For example:
   .Pp
   .Dl $ nc -l 1234
   .Pp
   .Nm
   is now listening on port 1234 for a connection.
   On a second console
   .Pq or a second machine ,
   connect to the machine and port being listened on:
   .Pp
   .Dl $ nc 127.0.0.1 1234
   .Pp
   There should now be a connection between the ports.
   Anything typed at the second console will be concatenated to the first,
   and vice-versa.
   After the connection has been set up,
   .Nm
   does not really care which side is being used as a
   .Sq server
   and which side is being used as a
   .Sq client .
   The connection may be terminated using an
   .Dv EOF
   .Pq Sq ^D .
   .Sh DATA TRANSFER
   The example in the previous section can be expanded to build a
   basic data transfer model.
   Any information 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.
   .Pp
   Start by using
   .Nm
   to listen on a specific port, with output captured into a file:
   .Pp
   .Dl $ nc -l 1234 \*(Gt filename.out
   .Pp
   Using a second machine, connect to the listening
   .Nm
   process, feeding it the file which is to be transferred:
   .Pp
   .Dl $ nc host.example.com 1234 \*(Lt filename.in
   .Pp
   After the file has been transferred, the connection will close automatically.
   .Sh TALKING TO SERVERS
   It is sometimes useful to talk to servers
   .Dq 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:
   .Pp
   .Dl $ echo \&"GET\&" | nc host.example.com 80
   .Pp
   Note that this also displays the headers sent by the web server.
   They can be filtered, using a tool such as
   .Xr sed 1 ,
   if necessary.
   .Pp
   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:
   .Bd -literal -offset indent
   $ nc localhost 25 \*(Lt\*(Lt EOF
   HELO host.example.com
   MAIL FROM: \*(Ltuser@host.example.com\*(Gt
   RCPT TO: \*(Ltuser2@host.example.com\*(Gt
   DATA
   Body of email.
   \&.
   QUIT
   EOF
   .Ed
   .Sh PORT SCANNING
   It may be useful to know which ports are open and running services on
   a target machine.
   The
   .Fl z
   flag can be used to tell
   .Nm
   not to initiate a connection,
   together with the
   .Fl v
   .Pq verbose
   flag,
   to report open ports.
   For example:
   .Bd -literal -offset indent
   $ nc -vz 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!
   .Ed
   .Pp
   The port range was specified to limit the search to ports 20 \- 30.
   .Pp
   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 necessary 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
   .Fl w
   flag, or perhaps by issuing a
   .Qq Dv QUIT
   command to the server:
   .Bd -literal -offset indent
   $ 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 Ready
   .Ed
 .Sh EXAMPLES  .Sh EXAMPLES
 .Bl -tag -width x  Open a TCP connection to port 42 of hostname, using port 31337 as
 .It Li "$ nc hostname 42"  the source port, with a timeout of 5 seconds:
 Open a TCP connection to port 42 of hostname.  .Pp
 .It Li "$ nc -p 31337 hostname 42"  .Dl $ nc -p 31337 -w 5 hostname 42
 Open a TCP connection to port 42 of hostname, and use port 31337 as  .Pp
 the source port.  Open a UDP connection to port 53 of hostname:
 .It Li "$ nc -w 5 hostname 42"  .Pp
 Open a TCP connection to port 42 of hostname, and timeout after  .Dl $ nc -u hostname 53
 five seconds while attempting to connect.  .Pp
 .It Li "$ nc -u hostname 53"  
 Open a UDP connection to port 53 of hostname.  
 .It Li "$ nc -s 10.1.2.3 example.host 42"  
 Open a TCP connection to port 42 of example.host using 10.1.2.3 as the  Open a TCP connection to port 42 of example.host using 10.1.2.3 as the
 IP for the local end of the connection.  IP for the local end of the connection:
 .It Li "$ nc -v hostname 42"  .Pp
 Open a TCP connection to port 42 of hostname, displaying some  .Dl $ nc -s 10.1.2.3 example.host 42
 diagnostic messages on stderr.  .Pp
 .It Li "$ nc -v -z hostname 20-30"  
 Attempt to open TCP connections to ports 20 through 30 of  
 hostname, and report which ones  
 .Nm  
 was able to connect to.  
 .It Li "$ nc -v -u -z -w 3 hostname 20-30"  
 Send UDP packets to ports 20-30 of example.host, and report which ones  Send UDP packets to ports 20-30 of example.host, and report which ones
 did not respond with an ICMP packet after three seconds.  responded with an ICMP packet after three seconds:
 .It Li "$ nc -l 3000"  .Pp
 Listen on TCP port 3000, and once there is a connection, send stdin to  .Dl $ nc -uvz -w 3 hostname 20-30
 the remote host, and send data from the remote host to stdout.  .Pp
 .It Li "$ echo foobar | nc hostname 1000"  Create and listen on a Unix Domain Socket:
 Connect to port 1000 of hostname, send the string "foobar"  .Pp
 followed by a newline, and move data from port 1000 of hostname to  .Dl $ nc -lU /var/tmp/dsocket
 stdout until hostname closes the connection.  
 .It Li "$ nc -U /var/tmp/dsocket"  
 Connect to a Unix Domain Socket.  
 .It Li "$ nc -lU /var/tmp/dsocket"  
 Create and listen on a Unix Domain Socket.  
 .El  
 .Sh SEE ALSO  .Sh SEE ALSO
 .Xr cat 1 ,  .Xr cat 1
 .Xr telnet 1  
 .Sh AUTHORS  .Sh AUTHORS
 Original implementation by *Hobbit*  Original implementation by *Hobbit*
 .Aq hobbit@avian.org .  .Aq hobbit@avian.org .
 .Pp  .br
 Rewritten with IPv6 support by Eric Jackson  Rewritten with IPv6 support by
 .Aq ericj@monkey.org .  .An Eric Jackson Aq ericj@monkey.org .
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