IP Subnet Mask Quick Cheat Sheet
Besides the fact that I am studying for another Microsoft test and staring at subnets all day long – I also get asked on a regular basis how many addresses can i get from a /24 subnet or what does 255.255.255.0 mean.
Let me break it down for you real quick like:
When you use 255.255.255.0 as your subnet you are limiting yourself to a network containing all the same ip’s except for the last number. Like 192.168.1.0 where the 0 changes. And using 255.255.0.0 Would limit you to the last two digits changing like 192.168.0.0 . Are you with me? It gets a little more complex with different subnets but here is a quick breakdown for you:
| Hosts | Netmask | Amount of a Class C | |
|---|---|---|---|
| /30 | 4 | 255.255.255.252 | 1/64 |
| /29 | 8 | 255.255.255.248 | 1/32 |
| /28 | 16 | 255.255.255.240 | 1/16 |
| /27 | 32 | 255.255.255.224 | 1/8 |
| /26 | 64 | 255.255.255.192 | 1/4 |
| /24 | 256 | 255.255.255.0 | 1 |
| /23 | 512 | 255.255.254.0 | 2 |
| /22 | 1024 | 255.255.252.0 | 4 |
| /21 | 2048 | 255.255.248.0 | 8 |
| /20 | 4096 | 255.255.240.0 | 16 |
| /19 | 8192 | 255.255.224.0 | 32 |
| /18 | 16384 | 255.255.192.0 | 64 |
| /17 | 32768 | 255.255.128.0 | 128 |
| /16 | 65536 | 255.255.0.0 | 256 |
Check out this IP Subnet Tool Calculator – MINT! http://www.syrex.co.za/ipcalc/
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about 2 years ago
Helpful chart!
Remember though the number of IP addresses isn’t the number of computers that can be on the network. It’s usually off by 3 – with IPs reserved for the Network address, the Broadcast address, and the gateway.
about 2 years ago
Actually it is off by 2 the formula is 2(n-32)-2 thats 2 to the nth power minus 32 which gives you the numbers in the chart and then you subtract 2 – no gateway is not a reserved address.
Thanks though Jay!
about 1 year ago
kindly suggest some good websites on computer networking
about 1 year ago
The quickest way to understand subnetting is that subnetting is a binary AND operation of all the octets in your IP address with the subnet mask. subnet binary 255 (11111111) always allows the octet to pass thru and becomes the same number in the network address. performing an AND operation if the mask octet is less that 255 will yield a consistent number that will become the lowest number of the network address octet. A smaller mask octet number will yield a wider network range for the chosen IP address, and this number range is 256 minus the mask octet. For example, a mask of 255.255.254.0 will yield a 2 x 255 address range for the chosen IP address. Lowest number in the range is the network address and the highest is the broadcast address.
about 6 months ago
Subnetting-Secrets Learn The Easy Way To Subnet
English | ISO | 356.05 MB
Genre: Video Training
Discover The Subnet
Introduction To Subnet
Easy Way To Subnet
Wildcard Mask
Designing Subnets
http://filetrack.blogspot.com/2011/07/subnetting-secrets-easy-way-to-subnet.html