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SG350-10P - Switch-Wide Packet Loss When Static LAG Partner Uncooperative?




I had horrible and intermittent packet loss across all 10 ports on my Cisco SG350-10P recently. I spent ages trying to diagnose it. Eventually I solved it by realising the Ubiquiti Unifi AC-HD access point did not have the option ticked "Enable port aggregation" so while my Cisco was set to bound the 2 ports into a static LAG, the access point would not have co-operated.


To be fair, the Unifi AP does say next to this option "Make sure to enable port aggregation on the downstream switch after enabling port aggregation on the AP." but I did not expect the issue to take out the whole switch (at best just the Unifi port I was expecting to see packet loss)


The thing that threw me is apart from a flood, why would one port be able to cause issues across all the other ports on a switch? I thought the switch was designed that 1 port should not affect another?


I presume that the Cisco would have been seeing an incorrect Link Layer presented to it.. but I could not see anything in the logs reporting this.


Most of my searches about LAG end up talking about LACP, which I have explicitly disabled. What does refusing to participate in Static LAG do that could cause a problem for the switch?


...and finally... is this a bug in the Cisco switch?

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