Subnetting

[chris128]

Most of the places I have worked at have had the bog standard class C subnet (subnet mask 255.255.255.0) so you just have one subnet with up to 254 hosts, e.g 192.168.20.1 - 192.168.20.254.
However, somewhere I went to today had the following subnet mask (which is still class C apparently) : 255.255.254.0

Now I'm no expert at subnetting etc but I am keen to learn so I have been trying to find out for myself what advantage this gives you over a 255.255.255.0 subnet mask. So I did a bit of reading up just now on how subnet mask's work and I'm still a bit puzzled.

Apparently when you convert a subnet mask down to binary then all of the bits that are set (ie have a 1 in them) represent the network part of the subnet, and the bits that are not set (ie are 0) represent the host part.
So in as 255 converts to 11111111 in binary then that means 255.255.255.0 has all of the first 3 octets set to 1s (network) and the last octet is for the host, which is fine and makes sense.
e.g

   255      255       255         0
11111111  11111111  11111111  00000000

However, when I converted 255.255.254.0 to binary (maybe I did it wrong), it gives me this:

   255      255       254         0
11111111  11111111  11111110  00000000

and as that last bit in the 254 part that is set to 0 is only capable of representing a 1 (as opposed to 2, 4, 8, 16, 32 etc) then does that mean that this subnet mask can only have 2 subnets in it or what? I dont quite understand what its telling me... I know they have at least two subnets running at the moment (192.168.10.X and 192.168.11.X) but are they the only possible subnets they could have? I doubt that but from looking at the bits I would have thought they couldnt even have those ones that they have got... so I obviously am missing something

Can anyone explain at all?

Thanks
Chris