Clients cannot obtain IP addresses through DHCP after the DHCP relay agent is upgraded

This problem may occur on a fixed switch in the following scenario:
- The switch was upgraded from V100R002/V100R003 to V100R005/V100R006.
- The switch functions as a DHCP relay agent and is configured with the dhcp relay information enable command.
- An authentication mechanism is enabled before the DHCP server allocates an IP address to a client. The authentication server authenticates the client based on the option 82 field.
After the dhcp relay information enable command is configured on the switch, the interface name that the switch encapsulates in the DHCP option 82 field varies according to the system software version:
- For V100R003 and earlier versions, a VLANIF interface name is encapsulated.
- For V100R005 and later versions, a physical interface name is encapsulated.
As different interface names may be encapsulated in the option 82 field before and after the upgrade, the authentication server may fail to authenticate the user based on the option 82 field. If this problem occurs, modify the user authentication configuration on the authentication server after the upgrade. To be specific, change the content of the option 82 field on the authentication server to the physical interface name, or change the user authentication policy by disabling DHCP option 82 field-based authentication.

Other related questions:
DHCP client cannot obtain a correct IP address
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