What is meant by thrashing the mac table

[aizaz]

I dont know how can a mac table or filter/forward table can get thrashed if there is a situation of looping??? i mean at layer 2 if a switch receives copies of frames at ports how its going to effect the table it will just forward the frame and will know which device lies where so y is it that thrashing occurs ??

 

[Hawkeye22]

Because it has to keep udpating the MAC table swapping the two or more ports that MAC address is seen on. This would probably spike the cpu in the switch and sort of cause a denial of service.

I'm not real knowledgebal about the inner workings of switches, but if the MAC table can only hold one unique mac address per port, then the above will happen.