From the course: Subnetting in Your Head
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Determine subnets from an address
From the course: Subnetting in Your Head
Determine subnets from an address
- [Bill] Starting with an IP address and a subnet mask, determine the number of subnets and hosts per subnet. Start by looking at the first octet of the IP address. If this were a classful address, would this be Class A, Class B, or Class C? Use this to determine the classful subnet mask. This reverse engineers the answer to step one, where am I now, or in this case, where would the classful network range begin? Then determine how many extra bits the subnet mask contains as compared to its classful subnet mask. Now apply the formula to determine the number of subnets, which is two to the power of S, where S is the number of subnet bits that have been added to the classful subnet mask. Now apply the formula to determine the number of hosts per subnet, which is two to the power of H minus two, where H is the number of host bits that are remaining. You've now reverse engineered the subnetted address to determine the number of subnets and the number of hosts per subnet.
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