# Re: Determining hosts/subnets

When designing a network, say you're looking to get a certain amount of hosts & subnets. Using the Network IP address, what's the best way to go about figuring that out? Is there a math formula that you can use?

• MCSE: Cloud Platform and Infrastructure, MCSA: Windows Server 2003/2012/2016, CCNA Routing & Switchi Bay Area, CaliforniaMod Posts: 5,163 Mod
That's a classic CCENT/CCNA type of question, those tests would give you the number of hosts and/or subnets you'd need so you could figure out where to start with the binary math. The short answer is that you're going to have to learn how subnetting works to figure out the answer to questions like that. There are lots of threads on the subject here on TechExams, and you can take a look at something like Learn To Subnet for a more comprehensive howto.

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• 2^x where x = # of network or host bits.

For example, if you have a class C network, and need to subnet it into 4 equal subnets, your formula would look like 4 = 2^x, where "x" is the number of host bits you will have to borrow. 2^2 = 4, so you would need to borrow 2 bits from the host to make 4 subnets.

If you need 64 hosts per subnet, your formula is 64 = 2^x. 2^6 = 64 so you need at least 6 bits if you need 64 hosts. However, you have to factor in the network address/broadcast address, so if you only really have 62 usuable hosts address
• Slowhand wrote: »
That's a classic CCENT/CCNA type of question, those tests would give you the number of hosts and/or subnets you'd need so you could figure out where to start with the binary math. The short answer is that you're going to have to learn how subnetting works to figure out the answer to questions like that. There are lots of threads on the subject here on TechExams, and you can take a look at something like Learn To Subnet for a more comprehensive howto.

Thanks, yeah I came across a question like that the other day and was stumped. Most practice exams generally will give you the #of hosts/subnets. Thanks!
• pham0329 wrote: »
2^x where x = # of network or host bits.

For example, if you have a class C network, and need to subnet it into 4 equal subnets, your formula would look like 4 = 2^x, where "x" is the number of host bits you will have to borrow. 2^2 = 4, so you would need to borrow 2 bits from the host to make 4 subnets.

If you need 64 hosts per subnet, your formula is 64 = 2^x. 2^6 = 64 so you need at least 6 bits if you need 64 hosts. However, you have to factor in the network address/broadcast address, so if you only really have 62 usuable hosts address

Thanks! I'll have to make up some of my own questions here.... don't see those types very often.