HP 6125G HP 6125G & 6125G/XG Blade Switches Fundamentals Configuration - Page 127

Using DHCP to obtain an IP address and other configuration information, Address acquisition process

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Using DHCP to obtain an IP address and other configuration information Address acquisition process As previously mentioned, 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 67 or the file field-Obtains the configuration file name. The device resolves Option 67 first. If Option 67 contains the configuration file name, the device does not resolve the file field. If not, the device resolves the file field. • Option 66-Obtains the TFTP server domain name • Option 150-Obtains the TFTP server IP address • Option 6-Obtains the DNS server IP address. If no response is received from the DHCP server, the device removes the temporary configuration and starts up with the factory defaults. The temporary configuration contains two parts: the configuration made on the interface through which automatic configuration is performed, and the ip host command in the host name file. The temporary configuration is removed by executing the corresponding undo commands. For more information about DHCP, see Layer 3-IP Services Configuration Guide. For more information about the ip host command, see Layer 3-IP Services Command Reference. Principles for selecting an address pool on the DHCP server 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-A dynamic address pool contains a range of IP addresses and other parameters that the DHCP server dynamically assigns to clients. • Static address pool-A 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: • If devices use the same configuration file, you can 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. In this case, the configuration file can only contain common configurations of the devices, and the specific configurations of each device need to be performed in other ways. For example, the configuration file can enable Telnet and create a local user on devices so the administrator can Telnet to each device to perform specific configurations (for example, configure the IP address of each interface). • If devices use different configuration files, you need to configure static address pools to make sure each device can get a fixed IP address and a specific configuration file. With this method, no more configuration is required for the devices. 121

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121
Using DHCP to obtain an IP address and other configuration
information
Address acquisition process
As previously mentioned, 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 67 or the file field
—
Obtains the configuration file name. The device resolves Option 67 first.
If Option 67 contains the configuration file name, the device does not resolve the file field. If not, the
device resolves the file field.
•
Option 66
—
Obtains the TFTP server domain name
•
Option 150
—
Obtains the TFTP server IP address
•
Option 6
—
Obtains the DNS server IP address.
If no response is received from the DHCP server, the device removes the temporary configuration and
starts up with the factory defaults.
The temporary configuration contains two parts: the configuration made on the interface through which
automatic configuration is performed, and the
ip host
command in the host name file. The temporary
configuration is removed by executing the corresponding
undo
commands.
For more information about DHCP, see
Layer 3—IP Services Configuration Guide.
For more information
about the
ip host
command, see
Layer 3—IP Services Command Reference
.
Principles for selecting an address pool on the DHCP server
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
—
A dynamic address pool contains a range of IP addresses and other
parameters that the DHCP server dynamically assigns to clients.
•
Static address pool
—
A 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:
•
If devices use the same configuration file, you can 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. In this case, the configuration file can only contain common configurations
of the devices, and the specific configurations of each device need to be performed in other ways.
For example, the configuration file can enable Telnet and create a local user on devices so the
administrator can Telnet to each device to perform specific configurations (for example, configure
the IP address of each interface).
•
If devices use different configuration files, you need to configure static address pools to make sure
each device can get a fixed IP address and a specific configuration file. With this method, no more
configuration is required for the devices.