User Guide

Chapter 4. Configuring Special Features 79
Defining Option Types
Concepts
A DHCP option is a code, length, or value. An option also has a “type” (byte, word, long, longint, binary, IP
address, string).
The subnet mask, router gateway, domain name, domain name servers, NetBios name servers are all DHCP
options. Refer to RFC 1533 if you require more information.
Usually users will
not
need to define their own option types. The list of predefined option types based on RFC
1533 can be shown by typing
dhcp list definedoptions.
Commands
The following commands are available for adding/deleting option types:
dhcp add
<
code
> <
min
> <
max
> <
type
>
To list option types that are currently defined, use:
dhcp list definedoptions...
To list the definitions for all known options, use:
dhcp list definedoptions
To get help information, use:
dhcp list definedoptions?
To list the definition for option 1, if option 1 is defined, type:|
dhcp list definedoptions 1
To list the definition for all options that are well-known AND have a name starting with “h”, type:
dhcp list definedoptions h
Example:
To define a new option with a code of 128, a minimum number of IP addresses of 1, a maximum number of
IP addresses of 4, of type “IP address”, type:
dhcp add 128 1 4 ipAddress
This information implies that:
• Some DHCP client will know about the option with code 128.
• Option 128 allows IP addresses.
• The server can have a minimum of 1 IP address.
• The server can have up to 4 IP addresses.
• The administrator will still need to set the option value either globally, specific to a subnetwork, or
specific to a client for the option to have any meaning.
To delete the definition of the option with code 128, type:
dhcp del 128