rinetd/rinetd.8

.TH rinetd 8 "2021-02-19" "rinetd 0.73"

.SH NAME
rinetd \- internet redirection server

.SH SYNOPSIS
\fBrinetd\fR
[\fB\-f\fR]
[\fB\-c\fR \fIconfiguration\fR]
.br
\fBrinetd \-h\fR
.br
\fBrinetd \-v\fR

.SH DESCRIPTION
.PP
\fBrinetd\fR
redirects TCP or UDP connections from one IP address and port to another.
\fBrinetd\fR is a single-process server which handles any number of connections to
the address/port pairs specified in the file \fI/etc/rinetd.conf\fR. Since
\fBrinetd\fR runs as a single process using nonblocking I/O, it is able to redirect a
large number of connections without a severe impact on the machine. This makes
it practical to run services on machines inside an IP masquerading firewall.
.PP
\fBrinetd\fR is typically launched at boot time, using the following syntax:
.PP
\fB    /usr/sbin/rinetd\fR
.PP
The configuration file is found in the file \fI/etc/rinetd.conf\fR, unless
another file is specified using the \fB\-c\fR command line option.

.SH OPTIONS
.TP
\fB\-f\fR
Run \fBrinetd\fR in the foreground, without forking to the background.
.TP
\fB\-c\fR \fIconfiguration\fR
Specify an alternate configuration file.
.TP
\fB\-v\fR
Display the version number and exit.
.TP
\fB\-h\fR
Produce a short help message and exit.

.SH FORWARDING RULES
.PP
Most entries in the configuration file are forwarding rules. The
format of a forwarding rule is as follows:
.PP
\fB    bindaddress bindport connectaddress connectport [options...]\fR
.PP
For example:
.PP
\fB    206.125.69.81 80  10.1.1.2 80\fR
.PP
Would redirect all connections to port 80 of the "real" IP address
206.125.69.81, which could be a virtual interface, through \fBrinetd\fR to port
80 of the address 10.1.1.2, which would typically be a machine on the inside of
a firewall which has no direct routing to the outside world.

.PP Although responding on individual interfaces rather than on all interfaces
is one of \fBrinetd\fR's primary features, sometimes it is preferable to
respond on all IP addresses that belong to the server. In this situation, the
special IP address 0.0.0.0 can be used. For example:

.PP
\fB    0.0.0.0 23  10.1.1.2 23\fR
.PP
Would redirect all connections to port 23, for all IP addresses
assigned to the server. This is the default behavior for most
other programs.
.PP
Ports default to TCP. To specify the protocol, append \fI/udp\fR
or \fI/tcp\fR to the port number:
.PP
\fB    206.125.69.81 80/tcp  10.1.1.2 8000/udp\fR
.PP
Service names can be specified instead of port numbers. On most systems,
service names are defined in the file \fI/etc/services\fR.
.PP
Both IP addresses and hostnames are accepted for
bindaddress and connectaddress, including IPv6.
.PP

.SS UDP timeout option
Since UDP is a connectionless protocol, a timeout is necessary or forwarding
connections may accumulate with time and exhaust resources. By default, if
no data is sent or received on a UDP connection for 72 seconds, the other
connection is closed. This value can be changed using the \fItimeout\fR option:
.PP
\fB    0.0.0.0 8000/udp  10.1.1.2 80  [timeout=3600]\fR
.PP
This rule will forward all data received on UDP port 8000 to host 10.1.1.2
on TCP port 80, and will close the connection after no data is received on
the UDP port for 3600 seconds.

.SS Source address option
A forwarding rule option allows to bind to a specific local address when
sending data to the other end. This is done using the \fIsrc\fR option:
.PP
\fB    192.168.1.1 80  10.1.1.127 80  [src=10.1.1.2]\fR
.PP
Assuming the local host has two IP addresses, 10.1.1.1 and 10.1.1.2, this
rule ensures that forwarded packets are sent using source address 10.1.1.2.

.SH ALLOW AND DENY RULES
Configuration files can also contain allow and deny rules.
.PP
Allow rules which appear before the first forwarding rule are
applied globally: if at least one global allow rule exists,
and the address of a new connection does not
satisfy at least one of the global allow rules, that connection
is immediately rejected, regardless of any other rules.
.PP
Allow rules which appear after a specific forwarding rule apply
to that forwarding rule only. If at least one allow rule
exists for a particular forwarding rule, and the address of a new
connection does not satisfy at least one of the allow rules
for that forwarding rule, that connection is immediately
rejected, regardless of any other rules.
.PP
Deny rules which appear before the first forwarding rule are
applied globally: if the address of a new connection satisfies
any of the global deny rules, that connection
is immediately rejected, regardless of any other rules.
.PP
Deny rules which appear after a specific forwarding rule apply
to that forwarding rule only. If the address of a new
connection satisfies any of the deny rules for that forwarding rule,
that connection is immediately rejected, regardless of any other rules.
.PP
The format of an allow rule is as follows:
.PP
\fB    allow|deny pattern\fR
.PP
Patterns can contain the following characters: \fB0\fR, \fB1\fR, \fB2\fR,
\fB3\fR, \fB4\fR, \fB5\fR, \fB6\fR, \fB7\fR, \fB8\fR, \fB9\fR, \fB.\fR
(period), \fB?\fR, and \fB*\fR. The \fB?\fR wildcard matches any one character.
The \fB*\fR wildcard matches any number of characters, including zero.
.PP
For example:
.PP
\fB    allow 206.125.69.*\fR
.PP
This allow rule matches all IP addresses in the 206.125.69 class C domain.
.PP
Host names are NOT permitted in allow and deny rules. The performance
cost of looking up IP addresses to find their corresponding names
is prohibitive. Since \fBrinetd\fR is a single process server, all other
connections would be forced to pause during the address lookup.

.SH LOGGING
\fBrinetd\fR is able to produce a log file in either of two formats:
tab-delimited and web server-style "common log format".
.PP
By default, \fBrinetd\fR does not produce a log file. To activate logging, add
the following line to the configuration file:
.PP
\fB    logfile log-file-location\fR
.PP
Example:
.PP
\fB    logfile /var/log/rinetd.log\fR
.PP
By default, \fBrinetd\fR logs in a simple tab-delimited format containing
the following information:
.PP
    Date and time
.PP
    Client address
.PP
    Listening host
.PP
    Listening port
.PP
    Forwarded-to host
.PP
    Forwarded-to port
.PP
    Bytes received from client
.PP
    Bytes sent to client
.PP
    Result message
.PP
To activate web server-style "common log format" logging,
add the following line to the configuration file:
.PP
\fB    logcommon\fR

.SH REINITIALIZING RINETD
.PP
The \fBkill -1\fR signal (\fISIGHUP\fR) can be used to cause \fBrinetd\fR
to reload its configuration file without interrupting existing
connections.
.PP
Under Linux\(tm the process id is saved in the file \fI/var/run/rinetd.pid\fR
to facilitate the \fBkill -HUP\fR. An alternate filename can be provided by
using the pidlogfile configuration file option.

.SH BUGS AND LIMITATIONS
.PP
\fBrinetd\fR only redirects protocols which use a single TCP or UDP
socket. This rules out FTP.
.PP
The server redirected to is not able to identify the host the client really
came from. This cannot be corrected; however, the log produced by \fBrinetd\fR
provides a way to obtain this information. Under Unix, Sockets would
theoretically lose data when closed with SO_LINGER turned off, but in Linux
this is not the case (kernel source comments support this belief on my part).
On non-Linux Unix platforms, alternate code which uses a different trick to
work around blocking close() is provided, but this code is untested.
.PP
The logging is inadequate. The duration of each connection should be logged.
.SH LICENSE
Copyright (c) 1997, 1998, 1999, Thomas Boutell and Boutell.Com, Inc.
.PP
Copyright (c) 2003\-2021 Sam Hocevar
.PP
This software is released for free use under the terms of
the GNU General Public License, version 2 or higher. NO WARRANTY
IS EXPRESSED OR IMPLIED. USE THIS SOFTWARE AT YOUR OWN RISK.
.SH CONTACT INFORMATION
See https://github.com/samhocevar/rinetd/releases for the latest release.
.PP
Thomas Boutell can be reached by email: boutell@boutell.com
.PP
Sam Hocevar can be reached by email: sam@hocevar.net
.SH THANKS
Thanks are due to Bill Davidsen, Libor Pechachek, Sascha Ziemann, the
Apache Group, and many others who have contributed advice
and/or source code to this and other free software projects.