Duplicate FDB static entry, what can happen?

  • 11 June 2021
  • 1 reply


below the scenario:

There are two switch: A and B

There are two phone: A and B

Phone A is connected to switch A

Phone B is connected to switch B

The MAC address of phone A is statically sticky on a port of switch A (that is active) AND statically sticky on a port of switch B (that is inactive).

The MAC address of phone B is statically sticky on a port of switch B.


What happen if phone A try to communicate with phone B?

Does the switch B forward frame destined to phone A to it’s port where there is stiched the phone A MAC ?

1 reply

Userlevel 6



I just tried to add my laptop MAC address statically to the switch I’m connected to. I added it to a port that is down. The dynamic entry (that you’d have on Switch B port facing Switch A normally) disappeared in favor of static entry. Now my pings are not working. I want my money back. ;)

It seems doing so is not even about flapping frames between two ports or picking the most recent or top entry for that MAC from an fdb, it’s just about cutting your device off.

What is the reason for that struggle you have? If you need some VLAN/security assignment to follow your phones as they migrate over time, please consider dynamic VLAN assignment with MAC authentication or CEP. Some scripting (UPM LLDP trigger + CLI/TCL/Python) should do the work as well.

The user guide might help in browsing for these, or let us know more on what you wish to achieve.


Hope that helps,