How to subnet.

Here is an IP subnetting cheat sheet I got from my ICND instructor.

The Column alingment got off a little but you should be able to put it into a spreadsheet and make it work.

Hope this helps someone as much as it helped me... thanks Bryan(my ICND instructor.

Bits 1 2 3 4 5 6 7 8
Bit Weight 128 64 32 16 8 4 2 1
Subnet Mask 128 192 224 240 248 252 254 255
Networks 2 4 8 16 32 64 128 256
Hosts 0 2 6 14 30 62 126 254


Bits 9 10 11 12 13 14 15 16
Bit Weight
Subnet Mask
Networks 512 1024 2048 4096 8192 16384 32768 65536
Hosts 510 1022 2046 4094 8190 16382 32766 65534

Interesting OCTET = octet in subnet mask with out a 0 or a 255

Increment = 256-subnet mask in interesting octet
Current Subnet = IP address in interesting octet /Increment

Then: Increment * (answer round to nearest whole number)
Next Subnet = Current Subnet + Increment
Broadcast Address = Next Subnet - 1
1st IP Address = Current Subnet + 1
Last IP Address = Broadcast Address - 1