dhcp option82 vendor-specific format

Usage Scenario

In EVPN active-active scenarios, DHCP users obtain IP addresses from DHCP servers in different subnets through DHCP relay-enabled gateways. Users in a subnet use the same gateway address. If the gateway address is carried as the destination IP address in a response packet from the DHCP server, the packet may not be sent to the gateway of the user. As a result, the user fails to go online. To resolve this problem, run the dhcp option82 vendor-specific insert enable command to enable a DHCP relay-enabled gateway to insert the Vendor-Specific suboption (suboption 9) of Option 82 into a DHCP packet. Then, run the dhcp option82 vendor-specific format command to configure a format for the Option 82 suboption 9 and encapsulate the IP address that uniquely identifies the gateway location into a DHCP request packet to be sent to the DHCP server. The DHCP server that supports the Option 82 reserves this suboption in the response packet. If the response packet is sent to a wrong gateway, the DHCP relay-enabled gateway forwards the packet to the correct gateway based on the IP address carried in the suboption 9.

Prerequisites

The interface has been enabled to insert the Vendor-Specific suboption (suboption 9) of Option 82 into a DHCP packet using the dhcp option82 vendor-specific insert enable command.

Precautions

If the Vendor-Specific suboption (suboption 9) is configured in both the system view and interface view, the configuration in the interface view takes effect.

The length of the Option 82 suboption 9 is subject to the configuration in the interface view and that in the system view. If the Option 82 field is too long after the suboption 9 is inserted, the suboption 9 will not be carried in the Option 82 field.

When this command is run to deploy gateways functioning as a DHCP relay, set the sub-option-num parameter to the same value for different gateways and set the ip-address parameter to the VTEP address of a specified gateway.