Guys,

Subnets are kind of like DMX but backwards.

255.0.0.0 listens to any address in A.0.0.1 through A.255.255.254. Basically 16 million addresses.

255.255.0.0 listens to any address B.B.0.1 through B.B.255.254. Basically 65,000 addresses. This would be like DMX 16 bit.

Then theres 255.255.255.0 which is C.C.C.1 through C.C.C.254. Which is only 254 addresses.

Even still, when I use Catalyst machines I go even tighter.
Since I never have more than 10 Catalysts (rarely) on the same show and never have more than say 3 controllers, I never have more than 16 computers on a subnet.

Therefore I use the Subnet Mask of 255.255.255.240 which only listens to 16 addresses. These are based on which address you start with. I usually set my devices to 10.100.100.x because nothing else uses it and it's easy to remember. I say 10 instead of 2 because 2 is public and if you accidentally plug into an outside network then problems happen.

So using 10.100.100.1 as my starting address, as long as all machines that need to listen to each other are between 10.100.100.1 and 10.100.100.16 then they will all hear just fine and outside traffic will be filtered.


Try looking here http://www.subnet-calculator.com/subnet.php?net_class=A
To see additional configuration types. Basically the tighter the subnet, the less rogue packets.