The Network Services > DHCP > Options tab allows to configure DHCP options. DHCP options are additional configuration parameters provided by a DHCP server to DHCP clients.
Example: For some VoIP phones, to provide them with the necessary information from your DHCP servers you have to create and activate three additional DHCP options on this page:
- filename: Name of the boot file.
- next-server: Name of the TFTP server which provides the boot file.
- 4 (time-servers): IP address of the time server.
DHCP options can have different scopes: They can e.g. be provided to selected hosts only, or from selected servers only, or even globally. For this reason it is possible to define different parameters for the same host. Some DHCP options are already defined on the DHCP > Servers tab, e.g., DNS server (option 6). In case of conflicting parameter values, the parameters are provided to the client according to the following priority:
- DHCP option with scope Host
- DHCP option with scope MAC prefix
- DHCP option with scope Vendor ID
- DHCP option with scope Server
- DHCP server parameter (DHCP > Servers tab)
- DHCP option with scope Global
Note – With the DHCP request, a DHCP client submits the information which DHCP options it can deal with. As a result the DHCP server only provides the DHCP options the client understands, no matter which options are defined here.
To create a DHCP option, proceed as follows:
Click New DHCP Option.
The Add DHCP Option dialog box opens.
Make the following settings:
Address type (only if IPv6 is enabled): Select the IP version which you create the DHCP option for.
Code: Select the code of the DHCP option you want to create.
Note – With the entry filename you can specify a file to be loaded into the DHCP client to be executed there. With next-server you define the boot server. The numbered DHCP option codes are defined in RFC 2132 and others.
Name: Enter a descriptive name for this option.
Type: Only available if you selected a code with the comment (unknown). Select the data type of the option. The data types IP Address, Text and Hex are available. Depending on the selected data type enter the appropriate data in the corresponding field below:
Address: Add or select the host or network group with the IP address(es) to be submitted with this DHCP option to the DHCP client. How to add a definition is explained on the Definitions & Users > Network Definitions > Network Definitions page.
Text: Enter the text to be submitted with this DHCP option to the DHCP client.
Hex: Enter the hexadecimal value to be submitted with this DHCP option to the DHCP client. Please note that you have to enter the groups of two hexadecimal digits separated by colons (e.g., 00:04:76:16:EA:62).
Integer: Enter the integer value to be submitted with this DHCP option to the DHCP client.
Scope: Define on which condition the DHCP option should be sent.
- Global: The DHCP option will be sent by all defined DHCP servers to all DHCP clients.
- Server: In the Server box, select the DHCP servers which should send the DHCP option. The box displays all DHCP servers defined on the DHCP Servers tab.
- Host: In the Host box, add or select the hosts which should be provided the DHCP option. How to add a definition is explained on the Definitions & Users > Network Definitions > Network Definitions page.
- MAC prefix: Enter a MAC prefix. All DHCP clients with a matching MAC address will be provided the DHCP option.
- Vendor ID: Enter a vendor ID or the prefix of a vendor ID. All DHCP clients which match this string will be provided the DHCP option.
Comment (optional): Add a description or other information.
The new DHCP option appears on the DHCP Options list and is immediately active.
To either edit or delete a DHCP option, click the corresponding buttons.