195 lines
7.6 KiB
Groff
195 lines
7.6 KiB
Groff
.\" dhclient.8
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.\"
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.\" Copyright (c) 1997 The Internet Software Consortium.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\"
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of The Internet Software Consortium nor the names
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.\" of its contributors may be used to endorse or promote products derived
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.\" from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE INTERNET SOFTWARE CONSORTIUM AND
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.\" CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
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.\" INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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.\" DISCLAIMED. IN NO EVENT SHALL THE INTERNET SOFTWARE CONSORTIUM OR
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.\" CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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.\" LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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.\" USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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.\" ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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.\" OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" This software has been written for the Internet Software Consortium
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.\" by Ted Lemon <mellon@fugue.com> in cooperation with Vixie
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.\" Enterprises. To learn more about the Internet Software Consortium,
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.\" see ``http://www.isc.org/isc''. To learn more about Vixie
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.\" Enterprises, see ``http://www.vix.com''.
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.TH dhclient 8
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.SH NAME
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dhclient - Dynamic Host Configuration Protocol Client
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.SH SYNOPSIS
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.B dhclient
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[
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.B -p
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.I port
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]
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[
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.B -1
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]
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[
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.B -D
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]
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[
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.B -d
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]
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[
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.I if0
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[
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.I ...ifN
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]
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]
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.SH DESCRIPTION
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The Internet Software Consortium DHCP Client, dhclient, provides a
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means for configuring one or more network interfaces using the Dynamic
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Host Configuration Protocol, BOOTP protocol, or if these protocols
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fail, by statically assigning an address.
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.SH OPERATION
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.PP
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The DHCP protocol allows a host to contact a central server which
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maintains a list of IP addresses which may be assigned on one or more
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subnets. A DHCP client may request an address from this pool, and
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then use it on a temporary basis for communication on network. The
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DHCP protocol also provides a mechanism whereby a client can learn
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important details about the network to which it is attached, such as
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the location of a default router, the location of a name server, and
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so on.
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.PP
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On startup, dhclient reads the
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.IR dhclient.conf
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for configuration instructions. It then gets a list of all the
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network interfaces that are configured in the current system. For
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each interface, it attempts to configure the interface using the DHCP
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protocol.
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.PP
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In order to keep track of leases across system reboots and server
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restarts, dhclient keeps a list of leases it has been assigned in the
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dhclient.leases(5) file. On startup, after reading the dhclient.conf
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file, dhclient reads the dhclient.leases file to refresh its memory
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about what leases it has been assigned.
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.PP
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When a new lease is acquired, it is appended to the end of the
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dhclient.leases file. In order to prevent the file from becoming
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arbitrarily large, from time to time dhclient creates a new
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dhclient.leases file from its in-core lease database. The old version
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of the dhclient.leases file is retained under the name
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.IR dhcpd.leases~
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until the next time dhclient rewrites the database.
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.PP
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Old leases are kept around in case the DHCP server is unavailable when
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dhclient is first invoked (generally during the initial system boot
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process). In that event, old leases from the dhclient.leases file
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which have not yet expired are tested, and if they are determined to
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be valid, they are used until either they expire or the DHCP server
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becomes available.
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.PP
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A mobile host which may sometimes need to access a network on which no
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DHCP server exists may be preloaded with a lease for a fixed
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address on that network. When all attempts to contact a DHCP server
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have failed, dhclient will try to validate the static lease, and if it
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succeeds, will use that lease until it is restarted.
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.PP
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A mobile host may also travel to some networks on which DHCP is not
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available but BOOTP is. In that case, it may be advantageous to
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arrange with the network administrator for an entry on the BOOTP
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database, so that the host can boot quickly on that network rather
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than cycling through the list of old leases.
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.SH COMMAND LINE
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.PP
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The names of the network interfaces that dhclient should attempt to
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configure may be specified on the command line. If no interface names
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are specified on the command line dhclient will identify all network
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interfaces, elimininating non-broadcast interfaces if possible, and
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attempt to configure each interface.
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.PP
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If dhclient should listen and transmit on a port other than the
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standard (port 68), the
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.B -p
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flag may used. It should be followed by the udp port number that
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dhclient should use. This is mostly useful for debugging purposes.
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If the
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.B -p
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flag is specified, the client will transmit responses to servers at a
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port number that is one less than the one specified - i.e., if you
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specify
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.B -p
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68, then the client will listen on port 68 and transmit to port 67.
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Datagrams that must go through relay agents are sent to the port
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number specified with the
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.B -p
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flag - if you wish to use alternate port numbers, you must configure
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any relay agents you are using to use the same alternate port numbers.
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.PP
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Dhclient will normally run in the foreground until it has configured
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an interface, and then will revert to running in the background.
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To run force dhclient to always run as a foreground process, the
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.B -d
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flag should be specified. This is useful when running dhclient under
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a debugger, or when running it out of inittab on System V systems.
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.PP
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The
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.B -D
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flag causes
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.B dhclient
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to save the script it creates for use in conjunction with
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.B dhclient-script
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in
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.IR /tmp.
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.PP
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The
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.B -1
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flag cause dhclient to try once to get a lease. If it fails, dhclient exits.
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.PP
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.SH CONFIGURATION
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The syntax of the dhclient.conf(8) file is discussed seperately.
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.SH FILES
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.B /etc/dhclient.conf, /var/db/dhclient.leases, /var/run/dhclient.pid,
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.B /var/db/dhclient.leases~.
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.SH SEE ALSO
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dhclient.conf(5), dhclient.leases(5), dhclient-script(8)
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.SH AUTHOR
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.B dhclient(8)
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has been written for the Internet Software Consortium
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by Ted Lemon <mellon@fugue.com> in cooperation with Vixie
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Enterprises. To learn more about the Internet Software Consortium,
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see
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.B http://www.vix.com/isc.
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To learn more about Vixie
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Enterprises, see
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.B http://www.vix.com.
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.PP
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This client was substantially modified and enhanced by Elliot Poger
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for use on Linux while he was working on the MosquitoNet project at
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Stanford.
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.PP
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The current version owes much to Elliot's Linux enhancements, but
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was substantially reorganized and partially rewritten by Ted Lemon
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so as to use the same networking framework that the Internet Software
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Consortium DHCP server uses. Much system-specific configuration code
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was moved into a shell script so that as support for more operating
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systems is added, it will not be necessary to port and maintain
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system-specific configuration code to these operating systems - instead,
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the shell script can invoke the native tools to accomplish the same
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purpose.
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.PP
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