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.\" $OpenBSD: dhcrelay.8,v 1.1 2004/04/12 21:10:28 henning Exp $
.\"
.\" Copyright (c) 1997 The Internet Software Consortium.
.\" 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. Neither the name of The Internet Software Consortium nor the names
.\" of its contributors may be used to endorse or promote products derived
.\" from this software without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND
.\" CONTRIBUTORS ``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 INTERNET SOFTWARE CONSORTIUM OR
.\" CONTRIBUTORS 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.
.\"
.\" This software has been written for the Internet Software Consortium
.\" by Ted Lemon <mellon@fugue.com> in cooperation with Vixie
.\" Enterprises. To learn more about the Internet Software Consortium,
.\" see ``http://www.isc.org/isc''. To learn more about Vixie
.\" Enterprises, see ``http://www.vix.com''.
.\"
.Dd January 1, 1997
.Dt DHCRELAY 8
.Os
.Sh NAME
.Nm dhcrelay
.Nd Dynamic Host Configuration Protocol Relay Agent
.Sh SYNOPSIS
.Nm dhcrelay
.Op Fl p Ar port
.Op Fl d
.Op Fl q
.Xo
.Oo Fl i Ar if0 Oo Ar ...
.Fl i Ar ifN Oc Oc
.Xc
.Ar server0 Op Ar ... serverN
.Sh DESCRIPTION
The Internet Software Consortium DHCP Relay Agent,
.Nm dhcrelay ,
provides a means for relaying DHCP and BOOTP requests from a subnet to which
no DHCP server is directly connected to one or more DHCP servers on other
subnets.
.Sh OPERATION
The DHCP Relay Agent listens for DHCP requests on all interfaces
attached to a host, unless one or more interfaces are specified on the
command line with the
.Fl i
flag.
.Pp
When a query is received,
.Nm
forwards it to the list of DHCP servers specified on the command line.
When a reply is received, it is broadcast or unicast on the network from
whence the original request came.
.Pp
It is possible to specify a set of interfaces on which
.Nm
will listen, so that if
.Nm
is connected through one interface to a network on which there is no DHCP
server, but is connected on another interface to a network on which there
is a DHCP server, it will not relay DHCP and BOOTP requests from the network
on which the server exists to that server.
This is an imperfect solution.
.Sh COMMAND LINE
The names of the network interfaces that
.Nm
should attempt to configure may be specified on the command line using the
.Fl i
option.
If no interface names are specified on the command line,
.Nm
will identify all network interfaces, eliminating non-broadcast interfaces
if possible, and attempt to configure each interface.
.Pp
If
.Nm
should listen and transmit on a port other than the standard (port 67), the
.Fl p
flag may used.
It should be followed by the UDP port number that
.Nm
should use.
This is mostly useful for debugging purposes.
If the
.Fl p
flag is specified, the relay agent will transmit responses to clients
at a port number that is one greater than the one specified \- i.e., if
you specify
.Fl p
67, then the relay agent will listen on port 67 and transmit to port 68.
Transmissions to servers will be sent to the same port number
that is specified with the
.Fl p
flag.
.Pp
.Nm
will normally run in the foreground until it has configured
an interface, and then will revert to running in the background.
To force
.Nm
to always run as a foreground process, the
.Fl d
flag should be specified.
This is useful when running
.Nm
under a debugger, or when running it out of inittab on System V systems.
.Pp
.Nm
will normally print its network configuration on startup.
This can be annoying in a system startup script \- to disable this
behaviour, specify the
.Fl q
flag.
.Pp
The name of at least one DHCP server to which DHCP and BOOTP requests
should be relayed must be specified on the command line.
.Sh SEE ALSO
.Xr dhclient 8 ,
.Xr dhcpd 8
.Pp
RFC 2132, RFC 2131.
.Sh AUTHORS
.Nm
has been written for the Internet Software Consortium by
.An Ted Lemon Aq mellon@fugue.com
in cooperation with Vixie Enterprises.
To learn more about the Internet Software Consortium, see
.Pa http://www.vix.com/isc .
To learn more about Vixie Enterprises, see
.Pa http://www.vix.com .
.Sh BUGS
Relayed DHCP traffic could actually safely be protected by IPsec, but
like
.Xr dhcpd 8
and
.Xr dhclient 8 ,
.Nm
will bypass IPsec for all its traffic.
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