Allied Telesis AT-SBx31CFC960 - Manual (Page 231)

SwitchBlade x3112 Chassis Switch and AT-SBx31CFC960 Card Installation Guide
231
21. Before reactivating the DHCP relay filtering option on the ports, wait for
the longest IP address lease on the network to expire. This information
is available on the DHCP server. For example, you should wait 12
hours if that is the longest lease time.
22. After waiting the longest lease time, use the SET DHCPRELAY
INTERFACE command to reactivate the DHCP relay filtering option on
those ports you noted in step 2c. This example of the command
enables filtering on port 1.2:
set dhcprelay interface=1.2 filter=on
This completes the upgrade procedure.