.\"	$OpenBSD: dhcrelay.8,v 1.17 2022/03/31 17:27:29 naddy Exp $
.\"
.\" Copyright (c) 1997 The Internet Software Consortium.
.\" All rights reserved.
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.\" modification, are permitted provided that the following conditions
.\" are met:
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" 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.
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.\" 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
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.\" ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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.\" OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
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.\" 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 $Mdocdate: March 31 2022 $
.Dt DHCRELAY 8
.Os
.Sh NAME
.Nm dhcrelay
.Nd Dynamic Host Configuration Protocol relay agent
.Sh SYNOPSIS
.Nm
.Op Fl dor
.Op Fl C Ar circuit-id
.Op Fl R Ar remote-id
.Fl i Ar interface
.Ar destination ...
.Sh DESCRIPTION
The
.Nm
utility 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.
.Pp
.Nm
listens for DHCP requests on a given interface.
When a query is received,
.Nm
forwards it to the list of DHCP destinations 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
The server might be a name, address or interface.
.Nm
will operate in layer 2 mode when the specified servers are interfaces,
otherwise it will operate in layer 3 mode.
.Pp
The name of at least one DHCP server to which DHCP and BOOTP requests
should be relayed,
as well as the name of the network interface that
.Nm
should attempt to configure,
must be specified on the command line.
.Pp
.Nm
supports relaying of DHCP traffic to configure IPsec tunnel mode
clients when listening on the
.Xr enc 4
interface using layer 3 mode only.
The DHCP server has to support RFC 3046 to echo back the relay agent
information to allow stateless DHCP reply to IPsec tunnel mapping.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl C Ar circuit-id
The
.Ar circuit-id
relay agent information sub-option value that
.Nm
should append on relayed packets.
If this option is not specified, it will use the interface number by default.
.It Fl d
Do not daemonize.
If this option is specified,
.Nm
will run in the foreground and log to
.Em stderr .
.It Fl i Ar interface
The name of the network interface that
.Nm
should attempt to configure.
For layer 3 mode at least one IPv4 address has to be configured on this
interface.
.It Fl o
Add the relay agent information option.
By default, this is only enabled for the
.Xr enc 4
interface.
.It Fl R Ar remote-id
The
.Ar remote-id
relay agent information sub-option value that
.Nm
should append on relayed packets.
If this option is not specified, it will use the destination address by default.
.It Fl r
Replace incoming Relay Agent Information with the one configured.
.El
.Sh SEE ALSO
.Xr dhclient 8 ,
.Xr dhcpd 8
.Sh STANDARDS
.Rs
.%A R. Droms
.%D March 1997
.%R RFC 2131
.%T Dynamic Host Configuration Protocol
.Re
.Pp
.Rs
.%A S. Alexander
.%A R. Droms
.%D March 1997
.%R RFC 2132
.%T DHCP Options and BOOTP Vendor Extensions
.Re
.Pp
.Rs
.%A M. Patrick
.%D January 2001
.%R RFC 3046
.%T DHCP Relay Agent Information Option
.Re
.Pp
.Rs
.%A B. Patel
.%A B. Aboba
.%A S. Kelly
.%A V. Gupta
.%D January 2003
.%R RFC 3456
.%T Dynamic Host Configuration Protocol (DHCPv4) Configuration of IPsec Tunnel Mode
.Re
.Sh AUTHORS
.An -nosplit
.Nm
was written by
.An Ted Lemon Aq Mt mellon@fugue.com .
.Pp
The current implementation was reworked by
.An Henning Brauer Aq Mt henning@openbsd.org .
.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.