DHCP Option 82 Configuration

DHCP option 82 is automatically enabled when you enable DHCP snooping on a VLAN. There are no additional configuration steps to enable DHCP option 82. Refer to Configuring DHCP snooping to enable DHCP snooping.

When processing DHCP packets, the ICX device applies the following default behavior when DHCP option 82 is enabled:

  • Subjects all ports in the VLAN to DHCP option 82 processing
  • Uses the general CID packet format
  • Uses the standard RID packet format
  • Replaces relay agent information received in DHCP packets with its own information
  • Does not enable SID processing

When DHCP option 82 is enabled, you can optionally:

  • Disable DHCP option 82 processing on individual ports in the VLAN, on all ports of the VLAN, or globally on all VLANs.
  • Configure the device to drop the DHCP packet with existing relay agent Information, or keep the relay agent information in a DHCP packet instead of replacing it with its own Information.
  • Configure Subscriber ID (SID), Circuit ID (CID) or Remote ID (RID) processing.

The following table details the supported configuration and expected functionality for DHCP option 82.

DHCP Option 82 Supported Configuration

Configuration Port-Config VLAN-Config Global-Config Functionality
Default. Enable Enable Enable Option 82 enabled
Disabled globally. Disable Disable Disable Option 82 disabled
Disabled globally, enabled on port. Enable Enable Disable Option 82 enabled
Disabled globally, enabled on port, disabled on VLAN. Enable Disable Disable Option 82 enabled
Enabled globally, enabled on port, disabled on VLAN. Enable Disable Enable Option 82 disabled
Enabled globally, disabled on port, disabled on VLAN. Disable Disable Enable Option 82 disabled
Enabled globally, disabled on port, enabled on VLAN. Disable Enable Enable Option 82 disabled
Disabled globally, disabled on port, disabled on VLAN. Disable Disable Disable Option 82 disabled

In this section:

  1. Disabling or Re-enabling DHCP Option 82 Processing on an Interface
    By default, when DHCP option 82 is enabled on a VLAN, DHCP packets received on all member ports of the VLAN are subject to DHCP option 82 processing. You can disable or re-enable this processing on one or more member ports of the VLAN.
  2. Disabling DHCP Option 82 Globally and Re-enabling it for an Interface
    By default, when DHCP option 82 is enabled on a VLAN, DHCP packets received on all member ports of the VLAN are subject to DHCP option 82 processing. You can disable or re-enable this processing globally for all VLANs. The following task disables DHCP option 82 globally for all VLANs so that it is not enabled when DHCP snooping is configured for VLAN 100. It then re-enables DHCP option 82 for a specified Ethernet interface.
  3. Disabling or Re-enabling DHCP Option 82 Processing on all VLAN Member Ports
    You can disable or re-enable DHCP option 82 processing globally, and disable and re-enable as necessary on specified VLANs. The following task disables DHCP option 82 globally. IP DHCP snooping is then enabled for VLANs 100, 200, and 300, but DHCP option 82 is not automatically enabled because it has been disabled globally. DHCP option 82 is then re-enabled on all ports for VLAN 100.
  4. Changing the DHCP Relay Agent Forwarding Policy
    When the device receives a message containing relay agent information, by default the device replaces the information with its own relay agent information. This behavior can be changed if required.
  5. Configuring DHCP Snooping Relay Information Sub-options
    You can configure DHCP relay agent sub-options such as the Subscriber ID (SID), Circuit ID (CID) or Remote ID (RID) options.
  6. Displaying DHCP Option 82 Information
    You can use various show commands to view information about DHCP option 82 processing.
  7. Configuring the Source IP Address of a DHCP Client Packet on the DHCP Relay Agent
    You can enable the DHCP server to know the source subnet or network of a DHCP client packet.
Parent topic: DHCP Relay Agent Information and Option 82 Insertion