topic Re: Mac-address-table full root cause in ExtremeSwitching (ERS)

Mac-address-table full root cause

darvid — Tue, 13 Oct 2026 13:58:16 GMT

Hi all
Three years later, the problem has resurfaced. It appears that certain devices are causing "flapping," preventing the MAC table from clearing normally.
I tried locking the negotiation to 100 Full and forcing the PoE mode, but nothing works - the flapping persists and mac-address-table keep growing. I change aging-time to 100 and 30, growing slowly, but steel growing.
Have you ever encountered this problem? What can be done, and why does "flapping" interfere with normal operation ?

ERS 3650,
Commend PoE HP make flapping

Thanks

Re: Mac-address-table full root cause

gene22dony — Wed, 14 Oct 2026 06:17:07 GMT

Hello,
I’ve seen similar issues on managed switches, and MAC address flapping is often caused by a Layer 2 loop, a faulty device or cable, or a device connected through multiple paths. When the same MAC address keeps appearing on different ports, the switch repeatedly updates its MAC table, which can prevent entries from aging out as expected. I would check the switch logs for MAC flapping notifications, identify the affected MAC addresses and ports, and disconnect devices one at a time to isolate the source. Also, check for loops, verify STP configuration, and inspect any connected switches, access points, or PoE devices. Changing the aging time or forcing speed and duplex usually won't fix the underlying cause. If the table continues growing even after isolating the suspected devices, checking the ERS 3650 firmware and switch resource utilization would be a good next step.

Best Regards

Re: Mac-address-table full root cause

darvid — Wed, 14 Oct 2026 10:33:42 GMT

This time, it involves a whole range of devices that had been working fine until today. I will investigate ths point with Commend provider.
It is the management of the MAC table entries that surprises me. While some devices are indeed flapping, they consistently present the same MAC address on the same port. Why does this prevent other addresses from being cleared when the aging time expires ?