HP A5800 Series User Manual

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Using DHCP to obtain an IP address and other configuration
information
Address acquisition process
As mentioned before, a device sets the first up interface as the DHCP client during startup. The DHCP client
broadcasts a DHCP request, where the Option 55 field specifies the information that the client wants to
obtain from the DHCP server such as the configuration file name, domain name and IP address of the TFTP
server, and DNS server IP address.
After receiving the DHCP response from the DHCP server, the device obtains the IP address and resolves the
following fields in the DHCP response:
• Option 6—Specifies the DNS server IP address.
• Option 66—Specifies the TFTP server domain name.
• Option 67 (or the file field that specifies the configuration file name)—If Option 67 contains the
configuration file name, the device does not resolve the file field. If not, the device resolves the file field.
The configuration file name is saved in the Option 67 or file field of the DHCP response. The device first
resolves the Option 67 field. If this field contains the configuration file name, the device does not resolve
the file field. If not, it resolves the file field.
• Option 150—Specifies the TFTP server IP address.
If no response is received from the DHCP server, the device removes the temporary configuration and starts
up with factory defaults.
The temporary configuration contains two parts: the configuration made on the interface through which
automatic configuration is performed, and the configuration made by executing the ip host commands in the
host name file The temporary configuration is removed by executing the undo commands. For more
information about DHCP and ip host, see Layer 3—IP Services Configuration Guide.
Selection principles for the DHCP server address pool
The DHCP server selects IP addresses and other network configuration parameters from an address pool for
clients. DHCP supports the following types of address pools:
• Dynamic address pool—Contains a range of IP addresses and other parameters that the DHCP server
dynamically assigns to clients.
• Static address pool—Contains the binding of an IP address and a MAC address (or a client ID). The
DHCP server assigns the IP address of the binding and specific configuration parameters to a
requesting client whose MAC address or ID is contained in the binding. In this way, the client can get
a fixed IP address.
Select address pools by using one of the following methods.
• Method I—If devices use the same configuration file, configure a dynamic address pool on the DHCP
server to assign IP addresses and the same configuration parameters (for example, configuration file
name) to the devices. The configuration file can only contain common configurations of the devices,
and the specific configurations of each device must be performed in other ways. For example, the
configuration file can enable Telnet and create a local user on devices so that the administrator can
Telnet to each device to perform specific configurations (for example, configure the IP address of each
interface).
• Method II—If devices use different configuration files, you must configure static address pools to ensure
that each device can get a fixed IP address and a specific configuration file. With this method, the
administrator does not need to perform any other configuration for the devices. To configure static

HP A5800 Series Specifications

General

Brand	HP
Model	A5800 Series
Category	Switch
Language	English