dbc0713b05
Pointed out by: ru
416 lines
11 KiB
Groff
416 lines
11 KiB
Groff
.\" $OpenBSD: nc.1,v 1.36 2005/01/07 10:11:31 jmc Exp $
|
|
.\"
|
|
.\" Copyright (c) 1996 David Sacerdote
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 3. The name of the author may not be used to endorse or promote products
|
|
.\" derived from this software without specific prior written permission
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
|
|
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
|
|
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
|
|
.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
|
|
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
|
|
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
|
|
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
|
|
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
|
|
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
|
|
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
|
|
.\"
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd January 30, 2005
|
|
.Dt NC 1
|
|
.Os
|
|
.Sh NAME
|
|
.Nm nc
|
|
.Nd arbitrary TCP and UDP connections and listens
|
|
.Sh SYNOPSIS
|
|
.Nm nc
|
|
.Bk -words
|
|
.Op Fl 46DEdhklnorStUuvz
|
|
.Op Fl e Ar IPsec policy
|
|
.Op Fl i Ar interval
|
|
.Op Fl p Ar source_port
|
|
.Op Fl s Ar source_ip_address
|
|
.Op Fl w Ar timeout
|
|
.Op Fl X Ar proxy_protocol
|
|
.Oo Xo
|
|
.Fl x Ar proxy_address Ns Oo : Ns
|
|
.Ar port Oc Oc
|
|
.Xc
|
|
.Op Ar hostname
|
|
.Op Ar port Ns Bq Ar s
|
|
.Ek
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Nm
|
|
(or
|
|
.Nm 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
|
|
.Xr telnet 1 ,
|
|
.Nm
|
|
scripts nicely, and separates error messages onto standard error instead
|
|
of sending them to standard output, as
|
|
.Xr telnet 1
|
|
does with some.
|
|
.Pp
|
|
Common uses include:
|
|
.Pp
|
|
.Bl -bullet -offset indent -compact
|
|
.It
|
|
simple TCP proxies
|
|
.It
|
|
shell-script based HTTP clients and servers
|
|
.It
|
|
network daemon testing
|
|
.It
|
|
a SOCKS or HTTP ProxyCommand for
|
|
.Xr ssh 1
|
|
.It
|
|
and much, much more
|
|
.El
|
|
.Pp
|
|
The options are as follows:
|
|
.Bl -tag -width Ds
|
|
.It Fl 4
|
|
Forces
|
|
.Nm
|
|
to use IPv4 addresses only.
|
|
.It Fl 6
|
|
Forces
|
|
.Nm
|
|
to use IPv6 addresses only.
|
|
.It Fl D
|
|
Enable debugging on the socket.
|
|
.It Fl d
|
|
Do not attempt to read from stdin.
|
|
.It Fl h
|
|
Prints out
|
|
.Nm
|
|
help.
|
|
.It Fl E
|
|
Shortcut for "-e 'in ipsec esp/transport//require' -e 'out ipsec
|
|
esp/transport//require'", which enables IPsec ESP transport mode in both
|
|
directions.
|
|
.It Fl e
|
|
If IPsec support is available, then one can specify the IPsec policies
|
|
to be used using the syntax described in
|
|
.Xr ipsec_set_policy 3 .
|
|
This flag can be specified up to two times, as typically one policy for
|
|
each direction is needed.
|
|
.It Fl i Ar interval
|
|
Specifies a delay time interval between lines of text sent and received.
|
|
Also causes a delay time between connections to multiple ports.
|
|
.It Fl k
|
|
Forces
|
|
.Nm
|
|
to stay listening for another connection after its current connection
|
|
is completed.
|
|
It is an error to use this option without the
|
|
.Fl l
|
|
option.
|
|
.It Fl l
|
|
Used to specify that
|
|
.Nm
|
|
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
|
|
.Fl p ,
|
|
.Fl s ,
|
|
or
|
|
.Fl z
|
|
options.
|
|
Additionally, any timeouts specified with the
|
|
.Fl w
|
|
option are ignored.
|
|
.It Fl n
|
|
Do not do any DNS or service lookups on any specified addresses,
|
|
hostnames or ports.
|
|
.It Fl o
|
|
.Dq Once-only mode .
|
|
By default,
|
|
.Nm
|
|
does not terminate on EOF condition on input,
|
|
but continues until the network side has been closed down.
|
|
Specifying
|
|
.Fl o
|
|
will make it terminate on EOF as well.
|
|
.It Fl p Ar source_port
|
|
Specifies the source port
|
|
.Nm
|
|
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
|
|
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.
|
|
.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.
|
|
It is an error to use this option in conjunction with the
|
|
.Fl l
|
|
option.
|
|
.It Fl t
|
|
Causes
|
|
.Nm
|
|
to send RFC 854 DON'T and WON'T responses to RFC 854 DO and WILL requests.
|
|
This makes it possible to use
|
|
.Nm
|
|
to script telnet sessions.
|
|
.It Fl U
|
|
Specifies to use Unix Domain Sockets.
|
|
.It Fl u
|
|
Use UDP instead of the default option of TCP.
|
|
.It Fl v
|
|
Have
|
|
.Nm
|
|
give more verbose output.
|
|
.It Fl w Ar timeout
|
|
If a connection and stdin are idle for more than
|
|
.Ar timeout
|
|
seconds, then the connection is silently closed.
|
|
The
|
|
.Fl w
|
|
flag has no effect on the
|
|
.Fl l
|
|
option, i.e.\&
|
|
.Nm
|
|
will listen forever for a connection, with or without the
|
|
.Fl w
|
|
flag.
|
|
The default is no timeout.
|
|
.It Fl X Ar proxy_version
|
|
Requests that
|
|
.Nm
|
|
should use the specified protocol when talking to the proxy server.
|
|
Supported protocols are
|
|
.Dq 4
|
|
(SOCKS v.4),
|
|
.Dq 5
|
|
(SOCKS v.5)
|
|
and
|
|
.Dq connect
|
|
(HTTPS proxy).
|
|
If the protocol 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
|
|
.Ar hostname
|
|
using a proxy at
|
|
.Ar proxy_address
|
|
and
|
|
.Ar port .
|
|
If
|
|
.Ar port
|
|
is not specified, the well-known port for the proxy protocol is used (1080
|
|
for SOCKS, 3128 for HTTPS).
|
|
.It Fl z
|
|
Specifies that
|
|
.Nm
|
|
should just scan for listening daemons, without sending any data to them.
|
|
It is an error to use this option in conjunction with the
|
|
.Fl l
|
|
option.
|
|
.El
|
|
.Pp
|
|
.Ar hostname
|
|
can be a numerical IP address or a symbolic hostname
|
|
(unless the
|
|
.Fl n
|
|
option is given).
|
|
In general, a hostname must be specified,
|
|
unless the
|
|
.Fl l
|
|
option is given
|
|
(in which case the local host is used).
|
|
.Pp
|
|
.Ar port Ns Op Ar s
|
|
can be single integers or ranges.
|
|
Ranges are in the form nn-mm.
|
|
In general,
|
|
a destination port must be specified,
|
|
unless the
|
|
.Fl U
|
|
option is given
|
|
(in which case a socket must be specified).
|
|
.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
|
|
Open a TCP connection to port 42 of hostname, using port 31337 as
|
|
the source port, with a timeout of 5 seconds:
|
|
.Pp
|
|
.Dl $ nc -p 31337 -w 5 hostname 42
|
|
.Pp
|
|
Open a UDP connection to port 53 of hostname:
|
|
.Pp
|
|
.Dl $ nc -u hostname 53
|
|
.Pp
|
|
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:
|
|
.It Li "nc -E example.host 42"
|
|
Open a TCP connection to port 42 of example.host using IPsec ESP for
|
|
incoming and outgoing traffic.
|
|
.It Li "nc -e 'out ipsec esp/transport//require' example.host 42"
|
|
Open a TCP connection to port 42 of example.host using IPsec ESP for
|
|
outgoing traffic only.
|
|
.Pp
|
|
.Dl $ nc -s 10.1.2.3 example.host 42
|
|
.Pp
|
|
Send UDP packets to ports 20-30 of example.host, and report which ones
|
|
responded with an ICMP packet after three seconds:
|
|
.Pp
|
|
.Dl $ nc -uvz -w 3 hostname 20-30
|
|
.Pp
|
|
Create and listen on a Unix Domain Socket:
|
|
.Pp
|
|
.Dl $ nc -lU /var/tmp/dsocket
|
|
.Pp
|
|
Connect to port 42 of hostname via an HTTP proxy at 10.2.3.4, port 8080:
|
|
.Pp
|
|
.Dl $ nc -x10.2.3.4:8080 -Xconnect hostname 42
|
|
.Sh SEE ALSO
|
|
.Xr cat 1
|
|
.Sh AUTHORS
|
|
Original implementation by *Hobbit*
|
|
.Aq hobbit@avian.org .
|
|
.br
|
|
Rewritten with IPv6 support by
|
|
.An Eric Jackson Aq ericj@monkey.org .
|