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Once you have decided that using DHCP will provide a benefit,
you will need to follow the steps below to set up a DHCP server.
Note that only one DHCP server per network subnet is required.
On the server system: Allocate a set of currently unused IP addresses (preferably
a contiguous block of addresses). For example: Pre-assign and register hostnames to the IP address
allocated above. Using the -h
option to the dhcptools(1M) command may be
useful. For example, the following line: dhcptools -h fip=15.1.48.50 no=30 sm=255.255.255.0 hn=devlab## |
This command will create a file /tmp/dhcphosts
that can be incorporated into your /etc/hosts
or DNS/NIS database. Designate a system to act as the DHCP server for
your network. This should be a system that is "always" available
to it's clients. Use the SAM application to configure the DHCP services
on this server. To do this: Start the interactive SAM application by typing sam.
(Note, you may need to set your DISPLAY
variable to use the graphical version) Double click on the icon Networking and Communications. Double click on the icon Bootable Devices. Double click on the icon DHCP Device Groups Booting
From this Server. You should now see a screen that lists any DHCP groups already
defined (there may not be any if DHCP is not already configured). To add the new group of IP addresses which you allocated
in Step 1, click on the Action menu item and choose Add DHCP Group. This should bring up a form with parameters to fill in. Now you will need to fill in the information on
this screen. Some information may require additional research if
you are not familiar with the terms or with your network. Title not available (Setting Up a DHCP Server ) - Group Name:
This can be any name that isn't already defined
as a DHCP group. For example: group1 - Subnet Address:
This is the portion of an IP address that is not
masked off by the subnet mask (see below). If you don't want to
figure this out, then just enter one of the IP addresses in the
range you picked along with the correct subnet mask and SAM will
take care of the calculation. For example: 15.1.48.50 - Subnet Mask:
This depends on the "class" of your network, and
basically determines how an IP address is separated into a network
number and a host specific number. Press F1 in this field for more
information. For example: 255.255.255.0 - Subnet Address Pool:
Press this button to select the range of IP addresses
that you allocated in Step 1. A new screen will be displayed where
you can enter the Start and End address. If there are addresses
within the range that you picked that you do not want allocated
via DHCP, you can use the Reserved Addresses button to specify those
(or ranges of them). - Allow Any Device Class:
The SAM default is to allow any type of DHCP device
to use the group of IP address you are configuring. This may be
undesirable if you use a different method (or a different DHCP server
or group) for managing systems such as PCs running Win95™
or NT™. If you want this range of addresses to be used only by HP-UX
systems, then unselect this button, and enter the text: "HewlettPackard.HP-UX"
in the text field provided. - AutomaticAllocation to Bootp Clients:
Leave this option disabled. Enabling it will cause
problems for bootp devices such as printers and terminals which
rely only on their preconfigured server to respond to their boot
request. - Accept New Clients:
Leave this option enabled. - Address Lease Time:
The lease time should be set sufficiently long so
that if a client system is temporarily out of service (off)
for a time, its lease will not expire too soon. Infinite leases will never expire and disable the IP-address
reclamation features of DHCP. For example: 2 weeks. - Boot file name:
You can leave this field blank. - AdditionalParams.:
There are many parameters that can be specified
in this screen for such things as the default routers, time server,
DNS server, and NIS domain. You can specify as much or as little
as you like in this area. Only the more basic parameters are actually used by installation
and boot configuration tools. - Callback Routines:
None is necessary.
Once the parameters are all filled in, then press
OK on the Add DHCP Group screen. SAM will then make the modifications
to the /etc/dhcptab file. You will now want to use the Action menu to Enable
boot Server (if it is not already enabled).
Now, new systems that are installed with HP-UX 10.20
(or newer) or booted with a pre-installed 10.20 (or newer) version
of HP-UX should contact this server to get an IP address lease and
other network information provided by the server.
Details of the DHCP Services When doing a cold install of the HP-UX
Operating system (version 10.20 or newer): The installation tools will broadcast out on the network for
any available DHCP servers. The first server to respond will be
chosen to provide the default network information that the user
is presented with. In the network parameters screen during a Cold Install, you
see the question: "Is this networking information only temporary?".
The "yes" or
"no" answer to
this implies the following: "no":
Answering "no"
(the default) means that if the IP address and hostname were leased
from an DHCP server, then that lease will be retained after the
install is done, so that the first boot of the system will attempt
to renew the same lease. "yes":
Answering "yes"
implies that the IP address and hostname lease should be returned
to the server after the installation is complete. In this case,
the first system boot will try to get a new lease. This is most
useful when the system is being installed on a network that is different
from its final destination. (This answer to the question can also be set in the configuration
file with instl_adm(1M) using the keyword
is_network_info_temporary).
When automating system installations, the DHCP services allows
systems to get networking information without the need to make a
mapping in the HPUX-Install configuration files (See instl_adm(1m)
and instl_adm(4)). When a system boots for the first time (either after
a Cold Install, or the first boot of a pre-loaded (Instant Ignition)
system): The auto_parms
tool, that lets you configure the system identity and basic configuration
parameters, will invoke the dhcpclient,
which will broadcast out to find a DHCP server. The server, in turn,
provides a default set of networking parameters. In both cold install and a first boot of a pre-loaded system,
if the user chooses not to use the IP address given by the DHCP
server, the tool will inform the DHCP server that it can release
the lease on it and give it to someone else. At each system boot: If a client system was initially set up using an IP address
that was leased by a DHCP server, that client will check to ensure
that the lease is still valid at each boot. In addition, the system
will start a daemon process (dhcpclient -m)
that will maintain and renew that lease while the system is running. If a system cannot contact the DHCP server from which it originally
got the IP address lease, it will try to contact other DHCP servers
in order to determine if it has been moved to a different network.
If this is the case, the system will write a message to the auto_parms
log file (/etc/auto_parms.log)
indicating that it has detected a move to a new subnet and that
it is attempting to request a new lease. If the new lease request
is successful, new networking configuration values supplied by the
DHCP server will automatically be applied.
Enabling DHCP on a System Not Initially Configured with
DHCP If a system has been set up without using DHCP, but you would
like to start using it, the following steps may be taken. | | | |  | NOTE: The system's hostname and IP address may change based
on what the DHCP server assigns to it the first time it boots. | | | | |
There are two methods for enabling DHCP on a system that is
not currently using it: The first method is to use SAM. Your system will now begin using DHCP after the next reboot.
Please note that all of the current networking parameters will be
overridden with new values supplied by the DHCP server. If
for some reason the system cannot contact a DHCP server during the
next reboot, it will continue to use its current networking parameters. If you suspect that your system had problem contacting the
DHCP server, you can examine the auto_parms
log file (/etc/auto_parms.log)
to determine if the lease request was successful. The second method for enabling DHCP over a particular
network interface is use a text editor (such as vi
or emacs) to
edit the /etc/rc.config.d/netconf
file. In the header of this file, you will find some brief instructions
regarding a variable named DHCP_ENABLE.
This variable is tied by an index number to an individual network
interface. For example, in the following block: INTERFACE_NAME[0]=lan0
IP_ADDRESS[0]=15.1.50.76
SUBNET_MASK[0]=255.255.248.0
BROADCAST_ADDRESS[0]=""
DHCP_ENABLE[0]=1 |
Here, the variables are instructing the system to use the
lan0 interface
when attempting to contact a DHCP server. Similarly, if the lease
request is successful, the above IP_ADDRESS
variable would be updated to reflect the new value supplied by the
DHCP server. If the DHCP_ENABLE
variable was set to 0
or if the variable did not exist, no DHCP operations would be attempted
over the corresponding network interface. As noted in the first method of enabling DHCP, if the variable
DHCP_ENABLE does
not exist for a particular interface, the SAM tool will display
a grayed out DHCP enable button. In this case, you will need to add the variable definition
to a specific interface variable block. As an example, you would
need to add DHCP_ENABLE[2]=1
to the following interface variable block in order to enable DHCP
on the lan1 interface: INTERFACE_NAME[2]=lan1
IP_ADDRESS[2]=15.1.50.89
SUBNET_MASK[2]=255.255.248.0
BROADCAST_ADDRESS[2]="" |
The contents of /etc/rc.config.d/netconf
for this definition block should now look like the following: INTERFACE_NAME[2]=lan1
IP_ADDRESS[2]=15.1.50.89
SUBNET_MASK[2]=255.255.248.0
BROADCAST_ADDRESS[2]=""
DHCP_ENABLE[2]=1 |
Correspondingly, you could disable DHCP over a particular
interface by setting the variable to "0". Again, as in the first method, the system will only begin
using DHCP after the next reboot.
Background Information on DHCP Design The DHCP protocol is implemented as extensions to the BOOTP
protocol, and in fact the HP-UX DHCP server daemon and the BOOTP
daemon are the same (bootpd(1M)). This daemon
reads two configuration files: /etc/bootptab
and /etc/dhcptab. The mapping of systems to IP addresses and lease time information
is kept in the DHCP database file /etc/dhcpdb.
Some amount of management of this database is provided by the dhcptools(1M)
command. On the client side, a command called /usr/lbin/dhcpclient
is used to contact the server to get an IP address lease. This command
has the ability to broadcast out onto the network prior to the network
interface being enabled. The dhcpclient
also serves as a daemon process that sleeps until the time that
it needs to renew the IP address lease, at which time it will re-contact
the server where it got the original lease in order to extend it. The dhcpclient
command is not intended to be run by users directly, and is called
by other tools during system bootup and installation. For More Information Refer to the auto_parms(1M) man page
and the dhcpdb2conf(1M) man page for more
information regarding the networking parameters which DHCP can supply. More information on DHCP in general can be found in the following
locations: Man pages: bootpd(1m)
dhcptools(1M)
auto_parms(1M)
dhcpdb2conf(1M) |
The Worldwide Web: http://web.syr.edu/~jmwobus/comfaqs/dhcp.faq.html |
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