Dell EMC SmartFabric OS10 User Guide Release 10.5.2

Option-82 with the Client and the Server in different VLANs

In this topology, Host1, Host2,and Host3 are the DHCP clients connected to the DHCP-relay-enabled switch. The DHCP clients and the DHCP server are part of different VLANs, VLAN 100 and VLAN 200, respectively.

In this scenario, the DHCP-relay-enabled switch floods the DHCP packets from the DHCP client in VLAN 100 and also forwards the DHCP packet with Option-82 set in the DHCP packet header to the DHCP Server in VLAN 200. If you configured Option-82, the DHCP server allocates the IP address based on Option-82. Otherwise, the DHCP server allocates the IP address from the subnet based on the giaddr value in the DHCP relay packet.

If you disabled Option-82 in the DHCP relay switch, the DHCP packets from the client forward without Option-82 and the DHCP server allocates the IP address based on the giaddr value, which is the VLAN IP address.

You can configure Option-82 at the Global level and interface level. When both the global and interface level Option-82 configuration is present, the configuration to disable Option-82 takes precedence. By default, Option-82 is enable both at Global and Interface levels.

Option-82 is enabled by default.

If you disable Option-82 Globally or at a specific Interface, Option-82 sub-options such as option 1,2,5,11,151,152 are also disabled.

If Global DHCP snooping is enabled after disabling Option-82 globally, an error message displays. Similarly, if you disable Option-82 Globally after enabling Global DHCP snooping, an error message displays.

If you enable DHCP snooping at the Interface level, you cannot disable the VLAN interface level Option-82. Similarly, if you disable Option-82 in the VLAN, you cannot enable DHCP snooping at the VLAN interface level.