Devices turning on & off will result in events like that. Normal behavior when the ports are connected to PC's and such. I would only be concerned if I saw STP flaps on ports going to other infrastructure devices like switches, firewall, routers, etc. Links that shouldn't be bouncing short of device failure or reboot. Also, port 17 connected to the iMac is toggling between 100Mbps and 1Gbps. I've seen this behavior on my wired Macs and often I hard set the port to 1Gbps to stabilize it.
... View more