GNS3 Duplex Mismatch – How to stop the log message

If you have run GNS3 for any time you will have most likely come across the error %CDP-4-DUPLEX_MISMATCH or GNS Duplex mismatch.
With physical cisco hardware when two devices are connected together and cdp is enabled, when there is a duplex mismatch an error log will be generated. This is very helpful for physical hardware but in GNS3 it seems to appear for no reason and even if you configure both interfaces to full duplex you still see the log.

02:50:20.579: %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on FastEthernet2/0 (not half duplex), with R4 FastEthernet0/0 (half duplex).
02:50:20.911: %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on FastEthernet2/1 (not half duplex), with R4 FastEthernet0/0 (half duplex).
02:50:20.839: %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on FastEthernet2/1 (not half duplex), with R4 FastEthernet0/0 (half duplex).

The simple way to stop these messages is to use the following command

R4(config)#no cdp log mismatch duplex

The other way to stop the message would be to disable cdp on every device.

As this is only a virtual environment you are not really concerned about duplex mismatches and the error can safely be ignored.

I hope this helps somebody with this very simple but annoying problem with GNS3