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DHCP, dhcp - Dynamic Host Configuration Protocol (DHCP) introductory
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 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.
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
· Configuration files that contain information needed to start the DHCP
· 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
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
The joind Daemon
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
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
· 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
· Brings down the interface if it cannot renew a lease.
The xjoin Graphical User Interface Program
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
DHCP Configuration Files
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:
client.pcy Governs the behavior of a DHCP client
Specifies names for dynamic host name
Contains an entry for each netmask that
is other than the standard A, B, or C
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.
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.
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.
Converts bootptab entries into
static IP entries for JOIN databases
Checks the JOIN IP address lease
database for internal consistency
dhcpcemu Emulates a DHCP client
Controls invocation of DHCP on the
dhcpparm Prints client DHCP parameters
Dumps fields from the DHCP dynamic
Adds, modifies, or deletes data in
the DHCP dynamic database
Registers hosts in the DHCP dynamic
Displays the contents of a specific
JOIN server database
Checks for the existence of a NIS
server on the network
Displays a client's IP address
Displays the contents of the
server's dynamic database
Displays a client's configuration
Dumps raw hash table contents for
Dumps raw binary tree contents for
A cluster member should never be a DHCP client. It should always use static
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),
Technical Overview, Network Administration: Services, JOIN Server
Administrator's Guide (/usr/doc/join/TOC.html), /etc/join/README-DB237
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