Wildcard mask – how and why?
When we all start networking we learn about subnet masks and then wildcard masks come along and wow, you have to learn what seem like a new method. Being the kind of guy who loves Cisco (i wanted to call our son Cisco, but my wife said no to that) the history side of Cisco is also something that i like. Now and again i find something out that i think “that is really cool” like did you know the CCIE numbers they give out to people that pass the exam did not start at number one! So when people ask who was the first CCIE, which to me is like asking who was the first man on the moon i can say Terry Slattery CCIE#1026.
Ok what does wildcard masks and Terry Slattery have in common?
Well, Terry helped create the CLI as we now know it. Terry was talking about wildcard masks and he ended the conversation with this little gem.
I had to jump in on the wildcard mask topic, because the idea of inverting the subnet mask has been around since the early days of Cisco training. I asked Kirk Lougheed, one of Cisco’s founders and the principal software developer at the begining, about why the wildcard mask uses the bits it does (i.e. 1 = don’t care). He told me that it was just a decision he made one day and that it could have gone either way.
They always say things are a way for a reason, the above would be just that.
The QOS study is going on and there is a lot of reading to do, the commands to learn are not that bad for the MQC. Once i start labbing i will get some inserts up to show what my lab is upto.