Dell EMC SmartFabric OS10 User Guide Release 10.5.2

Enable or disable DHCP Option-82

Use DHCP Option-82 in a distributed DHCP server or relay environment. When a network device, such as a DHCP, client sends a DHCP request, the relay agent inserts information about the client network location into the packet header of that request. The relay agent then sends the request to the DHCP server.

After the DHCP server sends a response, the relay agent strips out the DHCP Option-82 and forwards it to the client. DHCP Option-82 serves as enhancement to the DHCP request allowing the DHCP server to select a sub-range in the pool.

Use Option-82 to uniquely identify the client point of attachment. Option-82 carries two sub-options, circuit-id and remote-id:

• Circuit-id : This sub option contains the VLAN and port information of the DHCP client. The VLAN id and Port name are used for this option. The circuit-id is added in the <VLANID>-<INTERFACE_NAME> format. For example: vlan100-eth1/1/1.
• Remote-id : This sub option contains the system identification. System MAC address is used for this sub-option. For example: 00:04:89:76:62:78.

By default, Option-82 is enabled at both the Global level and interface level. When you disable Option-82, the relay agent forwards the packet without adding client information (Option-82 and its sub-options) to the packet header. The DHCP server allocates the IP address based on the giaddr value.

Restrictions and Limitations

• Enabling or disabling Option-82 is not supported on PVLAN. By default, Option-82 is always enabled on PVLAN.
• This feature is not supported on VXLAN.
• In case of a VLT configuration mismatch, discover and offer take one route where Option-82 is enabled but takes another route where Option-82 is disabled and the client never gets an IP address.