CCIE LAB TIP 3550/3560

During my practice to the lab exam, i am facing with some new stuff and some memory refreshers. for me as I was explaining before I have been handling mostly voice in the past ~7 years, I would like to give you a tip hopefully it is only a memory refresher When you face with a setup of a new Catalyst 3550/3560 you will face the lab with some layer 3 When you take the Catalyst fresh configuration and you are trying to put under x interface an IP Address you could be facing with this error Bad mask /xx for address x.x.x.x and why!? due to the fact that Cisco do not use the first subnet after subneting the network unless you tell it to. also called subnet zero so under global config simply put ! (config)#ip subnet-zero ! and like magic no more Bad mask message.