D-Link DWS-3160-24TC Reference Manual page 505

DWS-3160 Series Gigabit Ethernet Unified Switch Web UI Reference Guide
In other words, MBA and IMPB will not work when the MAC belongs to a tunnel client.
To achieve IP-in-IP tunnel forwarding, the MAC addresses of the devices under the tunnel are learned and marked
as "static" FDB entries on the Wireless Switch. These "static" entries would not be removed using the "clear fdb all"
command nor can they be erased by using the "delete fdb <vlan_name> <macaddr>" command. They also would
not aged out from the FDB table as long as the devices are still online.
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