How to configure DHCP Option 3 (Routers) to assign Multiple Gateway IP Addresses

08/23/2021 32 21303

DESCRIPTION:

The SonicWall DHCP server options feature provides support for DHCP options, also known as vendor extensions, as defined primarily in RFC 2131 and 2132. DHCP options allow users to specify additional DHCP parameters in the form of pre-defined, vendor-specific information that is stored in the options field of a DHCP message. When the DHCP message is sent to clients on the network, it provides vendor-specific configuration and service information.

"The router option specifies a list of IP addresses for routers on the  client's subnet.  Routers SHOULD be listed in order of preference. The code for the router option is 3.  The minimum length for the router option is 4 octets, and the length MUST always be a multiple of 4."  RFC 2132.

This article describes how to configure DHCP option 3 in the SonicWall.

RESOLUTION:

Resolution for SonicOS 6.5

This release includes significant user interface changes and many new features that are different from the SonicOS 6.2 and earlier firmware. The below resolution is for customers using SonicOS 6.5 firmware.

To configure DHCP Option objects, perform the following steps:

• Login to the SonicWall Management GUI
• Click Manage in the top navigation menu
• Navigate to the Network | DHCP Server page.
• Click on the Advanced button alongside the Enable DHCPv4 Server.
• In the DHCP Advanced Settings window, click on the Add Option.. button.
• In the Add DHCP Option Object window, enter the following:
  • Option Name: Enter a name for this object
  • Option Number: Select 3 (Routers)
  • Under Option Type, enter the IP addresses of the default gateways in order of preference. For example: 192.168.168.168;192.168.168.1
  • Enable check box Option Array to enter multiple values separated by a semi-colon (;).
  • Click on OK to save.

To assign the Option Object to a DHCP Lease Scope, perform the following steps:

• Click on configure on an already created DHCP Dynamic or Static Lease Scope. If not already created, create a new DHCP Dynamic or Static Lease Scope.
• Click on the Advanced tab in the configuration window.
• Under DHCP Generic Options, select the newly created DHCP Options Object.
• Enable checkbox Send Generic options always.
• Click on OK to save.

Resolution for SonicOS 6.2 and Below

The below resolution is for customers using SonicOS 6.2 and earlier firmware. For firewalls that are generation 6 and newer we suggest to upgrade to the latest general release of SonicOS 6.5 firmware.

To configure DHCP Option objects, perform the following steps:

• Login to the SonicWall Management GUI
• Navigate to the Network | DHCP Server page.
• Click on the Advanced button alongside the Enable DHCP Server check-box. Note: In Gen4 devices the Option Objects button is under DHCP Server Lease Scopes. Although the screenshot in this KB article are of a Gen5 NSA device, the options are similar in Gen4 devices.
• In the DHCP Advanced Settings window, click on the Add Option.. button.
• In the Add DHCP Option Object window, enter the following:
  • Option Name: Enter a name for this object
  • Option Number: Select 3 (Routers)
  • Under Option Type, enter the IP addresses of the default gateways in order of preference. For example: 192.168.168.168;192.168.168.1
  • Enable check box Option Array to enter multiple values separated by a semi-colon (;).
  • Click on OK to save.

• Click on configure on an already created DHCP Dynamic or Static Lease Scope. If not already created, create a new DHCP Dynamic or Static Lease Scope.
• Click on the Advanced tab in the configuration window.
• Under DHCP Generic Options, select the newly created DHCP Options Object.
• Enable checkbox Send Generic options always.
• Click on OK to save.