Subnetting

in my example i have the ip address 200.200.200.0 and i need three subnets. Im a little unsure on how to do this and have only managed to get 4 subnets, what do i do?

numbers of subnets go like this
1
2
4
8
16
32
64
128
256

in other words you can't.

if you where given an IP address of 200.200.200.0/24 then you would break it down into subnets by barrowing bits from the last octet. lets say you barrow 3 bits which would give you a /27 mask the way to figure how many subnets there would be is ( 2 to the 3rd power) -2) or 8-2=6 unless using VLSM. the number of hosts then would be (2 to the 5th power) -2) because there are 5 host bits left after barrowing 3 for the subnet. so with three bits barrowed you have enough to do the 3 subnets with 3 left over for expansion. If you are asking if you could get exactly 3 subnets then look at the post above mine and dont look at the 9th bit of 256 hehe

in was right all along!!

Thanx for the help

Adi

well almost if you are using a cisco router then you could barrow only 2 bits and enable ip subnet zero which would give you 3 usable subnets exactly. This however could pose a problem if you are hosting an older Unix box.

formula...
[ = 2^(mask bits) -2 ] and hosts/subnet [ = 2^(32 -16 -mask bits) -2 for class B]. The +1 in front of subnets should be added if ip subnet-zero command is used on Cisco router