Subnetting

No matter what entry level certification you are tryin to get ( CompTIA Network +, MCP, CCNA,) they all require subnetting the quick you can do i the better. Most time in a production environment you will probably only work with subnets /21-/24, this means max 2046 254 hosts receptively. This not only important to pass a test put also a very practical skill. And if are taking the cisco exam the it its even more important to strengthen your subnetting skills.




The main point of subnetting is taking a IP address range and using a smaller subnet mask to create more networks.
On the job as well as on a test the three main things that there to calculate in terms of subnetting, are what is the network ID of the a host, how many host are in a network with a given mask, and what is the broadcast address for a given network and it mask.This is one of the easy ways to me.

Subetting  Calculation tips

10.10.192.0 /21

255.255.248.0

A-find the broadcast address or next network ID

1. Subtract 256 (the maximum amout of address in any  one octet) from the value in which the subnet mask is different from all ones in this case in the thrid octet

256-192=8

2. add the diffference to network ID

192+8=200

3. the next network is would be 10.10.200.0

4. the address prceeding the network id is the broadcast address for the orginal network

10.10.199.255

10.10.195.26 /21

255.255.248.0

B-given a ip address find the net id

1. Subtract 256 (the maximum amout of address in any  one octet) from the value in which the subnet mask is different from all ones in this case in the thrid octet

256-192=8

2. Devide the value in the intersting octet (the octet where subnetting take places in the subnet mask in realtionship to the ip address) by the anwser in step 1

195/8=24,375 if there is a remainder drop the reamainder 24

3. Multiply this value by the anwser in step one

24x8=192

4. Place this value in the intresting octet

10.10.192.0