clear mac address dynamic possible effects?

[baselzind]

I have over 100 switches with L3 cores and many vlans , is dangerous to do this command "clear mac address dynamic" during production? does it have any adverse affects?

[MHM Cisco World]

for me I can not answer this 
but I have idea instead you can try clear mac for vlan, one by one this will effect only one VLAN not all vlan.

[balaji.bandi]

YES / NO - if you doing in Live network that will small impact on the service (some application may co-up) some may failed depends on environment you issuing this command.

why do you like to clear all MAC address ? (i would advise to do if that is necessary do task, in the maintance window or off peak hours).

if you have large database of MAC list - this will have impact on the CPU sometimes, since it floors with resolutions

[baselzind]

I do it because sometimes some new devices mac addresses doesn't show in the core show mac address or sometimes the same mac show on two interfaces. This command fixes this similar issues most of the time

[balaji.bandi]

instead of clear all the MAC, why not clear the MAC where required that minimise the risk. (how big MAC table ?) if small 10-20 ) you can do , but that is not best practice, also check why MAC table not cleared when the device move from 1 port to another ?

by the way what device is this ? IOS code ? can you show some example ?

[baselzind]

device is 6500 with WS-SUP720-BASE and version 12.2(33)SXI. But are you trying to say that doing that command could cause network wide issue?

[Georg Pauwen]

Hello,

I just tested this on a switch with about 10 computers. Continuous ping from all computers to a router did not have one single timeout, so it looks like noticeable impact is minimal to none...but I agree with @Joseph W. Doherty. Depending on what applications you have running on your network, even the most minimal 'interruption' might have an impact...

[Richard Burts]

The original poster mentions 2 reasons for wanting to clear the mac address table. "some new devices mac addresses doesn't show in the core show mac address". I would not be very concerned about this. Remembering that there is a time out for entries in the mac address table it would be normal that some device mac addresses would not be in the core mac address table - if the device has not recently sent a frame that reached the core switch.

The other reason "sometimes the same mac show on two interfaces" is a bit more concerning. I would suggest that rather than dealing with a symptom it would be better to try to identify why this is happening and then address the basic issue.

I agree with Joseph that the real answer is "it depends".  

[Joseph W. Doherty]

"does it have any adverse affects?"

Yes. Switch will flood unicast traffic for all (now) unknown destination MACs, until the cleared MACs are relearned.

Whether this cause a "visible" impact, is a "it depends" answer.