Hi Guys,

As an example, if we wanted to subnet our Class C network then depending on how many IP address' we wanted per subnet then do you:

subtract the number of IP address from 254?
For example, If we wanted 30 IP address' per subnet that would give us a subnet of 255.255.255.224 (254-30=224)

255.255.255.0 would be the first subnet network number
255.255.255.1 would be the first address
255.255.255.31 would be the broadcast address
with everything between 1 and 30 availible for client address'

255.255.255.32 would be the second subnet and so on....
giving 8 subnet's with 30 IP address

I hope that a) you guy's understand my poor way of explanation (this is how my mind has concepted it at the mo!) b)my theory is right! :blink

Well your theory works in this example, because it just happens to be a number that works
however I don't believe it would work for every random number you throw at it

Subnets as far as I recall require the bits to be set in sequence

for instance you can have a subnet of .224 (Binary = 11100000)
but you couldnt have a subnet of .226 (Binary = 11100010)

30 (or in essence, 32) just happens to be one of those power of 2 numbers that we know and love so well

Valid subnets follow the binary sequence from (10000000 to 11111110) and even 11111110 requires special software understanding to make use of

remember the sequence needs to be maintained, you cant have a gap in it or things that utilise subnets will get confused

10000000 = 128
11000000 = 192
11100000 = 224
11110000 = 240
11111000 = 248
11111100 = 252
11111110 = 254

You have to learn how to calculate the appropriate subnet mask for the given situation, not the precise number of hosts, as its often not possible, so if you required 22 IP addresses you would probably choose the same .224 subnet as the closest match with 30 hosts per subnet, as the next match in the sequence (240) only provides for 14 IP addresses, thus is of no use to your situation

its not very clear, subnetting is a beast of a subject, and I'm far from a master of the subject, let alone a good teacher of it, hope it helps a little

Thanks again Ryan :D
It looks like as far as the Network + exam goes as long as I have a good basic understanding I should be just fine :rolleyes:

When I was studying for my CCNA, I used "Learn to Subnet". It really made a difference. Click the link below to see for yourself.

http://www.learntosubnet.com/

Thanks Trip. What a cracking link :thumbleft