DHCP, dhcp - Dynamic Host Configuration Protocol (DHCP)
introductory information
The Dynamic Host Configuration Protocol (DHCP) enables you
to automatically assign IP addresses to clients on networks
from a pool of addresses. The IP address assignment
and configuration occurs automatically whenever appropriate
client systems (workstations and portable computers)
attach to a network. The Tru64 UNIX implementation of DHCP
is based on the JOIN product by JOIN Systems, Inc. (JOIN
is a trademark of JOIN Systems, Inc.)
Using DHCP has the following advantages: Automates IP
address administration Provides central configuration of
network computers Eliminates duplicate IP addresses Supports
older style BOOTP (on clients only)
DHCP Environment [Toc] [Back]
DHCP is based on the client-server model, in which client
systems request resources from other systems called
servers. A server is any host system or process that provides
a network service. A client is any host system or
process that uses services from a server.
A single host, or server, can provide more than one service.
Servers are passive; they do not call clients, they
wait for clients to call them.
The client always initiates the DHCP request. The server
answers the request, subject to its own configuration
rules.
DHCP Software [Toc] [Back]
The DHCP software contains the following components: Daemon
programs that handle communications between the server
(joind) and the client (joinc) A graphical user interface
program (xjoin) that sets up the dynamic DHCP databases
Configuration files that contain information needed to
start the DHCP daemons Administrative commands, such as
programs that enable you to configure and maintain DHCP
The following sections briefly describe these components.
For additional information, see the Network Administration:
Services guide and the JOIN Server Administrator's
Guide. The latter is provided by JOIN Systems, Inc. in
HTML format, and it can be accessed by opening the following
file with a web browser: /usr/doc/join/TOC.html
DHCP Daemons [Toc] [Back]
On the Tru64 UNIX system, the DHCP daemons (joind and
joinc) reside in the /usr/sbin directory. The following
sections describe the daemons and their tasks.
The joind Daemon [Toc] [Back]
The joind DHCP server daemon performs the following tasks:
Reads the /etc/bootptab configuration file and the
/etc/join/server.pcy policy file. Listens for client
hosts requesting BOOTP or DHCP information. Responds to
each client with an Internet address and other information
that allows the client to boot and configure its TCP/IP
stack. Supports both BOOTP and DHCP requests making the
bootpd daemon no longer necessary on the server.
The joinc Daemon [Toc] [Back]
The joinc DHCP client daemon performs the following tasks:
Reads the /etc/join/client.pcy policy file. Starts the
DHCP protocol handshake if requested to configure an
interface. Sends a request to the broadcast address for
the network or subnet. Receives configuration information,
configures and brings up the interface, and then
sleeps in the background until it needs to renew the
lease. Brings down the interface if it cannot renew a
lease.
The xjoin Graphical User Interface Program [Toc] [Back]
The xjoin graphical user interface program resides in the
/usr/bin/X11 directory, and enables you to configure the
DHCP server and set up the DHCP dynamic databases.
DHCP Configuration Files [Toc] [Back]
The /etc/bootptab file contains entries for DHCP and BOOTP
clients. You add, delete, and modify entries in this file
by using the xjoin program. The entries are then used by
the joind server daemon to configure the DHCP and BOOTP
clients.
The following table describes additional DHCP configuration
files that reside in the /etc/join directory:
-------------------------------------------------------
File Function
-------------------------------------------------------
client.pcy Governs the behavior of a DHCP client
namepool Specifies names for dynamic host name
assignment
netmasks Contains an entry for each netmask that
is other than the standard A, B, or C
masks
nets Specifies the networks to administer with
the joind daemon
server.pcy Governs the behavior of a DHCP server
-------------------------------------------------------
The client.pcy and server.pcy files contain information
about remote systems contacted by DHCP, the devices used
to contact these systems, the times to contact the systems,
and the level of access that remote systems can have
to the local system. You must edit the client.pcy file
using an editor. You modify the server.pcy file by using
the xjoin program. Configuring these files is optional.
The other files are configured by using the xjoin program.
Database Files [Toc] [Back]
Starting with DHCP Version 2.3.n, DHCP database files are
stored in a new format, one that is incompatible with
older formats. An online document explains the reasons
behind this change, lists the files that are affected, and
provides instructions for converting the files to the new
format. The document, README-DB237, and a conversion
utility, conv185-237, are located in the /etc/join directory.
Administrative Commands [Toc] [Back]
The following table lists the DHCP administrative commands
and their functions. These commands are used by joind,
joinc, or xjoin, and are not typically run by administrators.
------------------------------------------------
Command Function
------------------------------------------------
bptojdb Converts bootptab entries into
static IP entries for JOIN databases
checkdba Checks the JOIN IP address lease
database for internal consistency
dhcpcemu Emulates a DHCP client
dhcpconf Controls invocation of DHCP on the
client
dhcpparm Prints client DHCP parameters
jdbdump Dumps fields from the DHCP dynamic
databases
jdbmod Adds, modifies, or deletes data in
the DHCP dynamic database
jdbreg Registers hosts in the DHCP dynamic
databases
jdpshow Displays the contents of a specific
JOIN server database
probenis Checks for the existence of a NIS
server on the network
shleases Displays a client's IP address
leases
showdbs Displays the contents of the
server's dynamic database
showdhc Displays a client's configuration
files
showhash Dumps raw hash table contents for
debugging use
showtree Dumps raw binary tree contents for
debugging use
------------------------------------------------
A cluster member should never be a DHCP client. It should
always use static addressing.
If a cluster is to support a DHCP server, there can be
only one DHCP server for all the cluster members using a
common database with failover.
Commands: bptojdb(8), checkdba(8), dhcpcemu(8), dhcpconf(8), dhcpparm(8), jdbdump(8), jdbmod(8), jdbreg(8),
jdbshow(8), probenis(8), shleases(8), showdbs(8),
showdhc(8), xjoin(8)
Daemons: joinc(8), joind(8)
Files: bootptab(4) client.pcy(4), dhcptags(4), namepool(4), netmasks(4), nets(4), server.pcy(4)
Technical Overview, Network Administration: Services, JOIN
Server Administrator's Guide (/usr/doc/join/TOC.html),
/etc/join/README-DB237
DHCP(7)
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