Technical data

Configuring the DHCP Client
8.1 Key Concepts
8.1.1 Designating the Primary Interface
Some of the parameters that are configurable by DHCP are interface specific.
Examples of interface-specific parameters are the IP address and subnet mask.
Most DHCP configurable parameters, however, are systemwide configurable
parameters. Examples of systemwide parameters are the host name and DNS
domain name.
The TCP/IP Services DHCP client supports controlled configuration of systemwide
configurable items by designation of what is called the primary interface. The
primary interface is the interface on which the DHCP client will use systemwide
parameters received from the DHCP server to configure the system. Systemwide
parameters received on an interface that is not designated primary will not be
configured on your system by the DHCP client. There may be only one interface
on a system that is designated as the primary DHCP interface, but you are not
required to have any interface designated as the primary interface.
For example, if a system has multiple interfaces under DHCP control and the
system receives a different host name from a DHCP server on each of the DHCP
controlled interfaces, DHCP client uses the host name it receives on the primary
interface to configure the host name for the client.
If a system has multiple interfaces and only one is under DHCP control, you can
configure the systemwide parameters manually.
DHCP client uses the following rules to resolve conflicts:
• The only-one-primary-interface rule
This rule solves the potential conflict between two DHCP controlled interfaces
on a host getting different systemwide parameter values. To resolve the
conflict, you designate one interface to be the primary interface and
the parameters values that you receive on that interface are the values
DHCP client uses to configure the system. TCP/IP Services does not let you
designate two primary interfaces.
• The primary-interface-not-required rule
This rule solves the problem of DHCP configuring an interface (or interfaces)
with an IP address but also keeping manual control of the systemwide
parameters. In this case, DHCP client does not designate the interface as the
primary interface and ignores any systemwide parameters it receives from a
DHCP server.
Systemwide parameters are configured for a system as the last part of processing
the final message (a DHCPACK protocol message) from the DHCP server. DHCP
client, first configures the interface’s IP address, subnet mask, and broadcast
address; then, if the interface is designated as the primary interface, DHCP client
configures the systemwide parameters.
See Table 8–2 for a list of the DHCP configurable parameters supported by the
TCP/IP Services DHCP client.
8–2 Configuring the DHCP Client