I have base ip address 10.6.0.0/8 This is A class ip address. I need to divide this network into 12 subnets, and I need at least 80 computers in one network. Please explain how to calculate correctly subnets. I understand that subnets count should be power of two, so the nearest is 16. But I don't understand what should I do the next. Please explain. Thanks.
How to efficiently subnet a network
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If you're using the 10.0.0.0/8 private network, you've got 2^24 unique addresses to work with. If it is a single, contiguous network then we know that the 8 most significant bits are the network address, which in this case is just 10. We also know from basic IPv4 fundamentals that if 8 bits are used for the network address, 24 bits must be used for the host address. Setting all host bits to 0 yields the network address, and setting all host bits to 1 yields the segment broadcast address. Ergo, there are 2^24 - 2 available host addresses on a /8 network.
How to break this /8 into 12 individual subnets is entirely up to you as the network administrator. Since it's a private network, there's no need to pack addresses, this just creates headaches down the road. Working within octets is often the easiest, as you will see in a moment. First, lets step aside from classful addressing and step into the world of classless addressing.
Since IPv4 uses a binary address, each /8 network can be expressed as the sum of two /9 networks; each /9 as the sum of two /10 networks and so on. By telescoping these together we find out that a /8 can be subdivided into 256 /16 networks (formerly called class B). Similarly, each /16 can be subdivided into 256 /24 networks (formerly class C), and by extension each /8 can be subdivided into 65536 /24 networks. Now, you need at least one subnet with 80 hosts. A /26 network provides only 62 hosts so it is too small, a /25 network provides 126 hosts so it is just large enough. However, the textual representation of more than two /25 networks spans multiple octets so they may be a bit harder to remember; since packing is not a concern, it may be best to use only /24 networks which provide 254 hosts each and leave the last octet purely for host addresses. Visually this looks like 10.XXX.XXX.YYY where X is the private subnet and Y is the host. Creating 12 contiguous subnets would start at 10.0.0.YYY and end at 10.0.11.YYY. The subnet mask provides for subnets all the way up to 10.255.255.YYY
McHenryB
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RFC 1918 recommends using the 256 networks within the 192.168.0.0 block if subnetting is a problem. Whether you care to call those networks subnets or not is merely semantics. Almost all routers, certainly consumer ones, treat those as separate networks.
McHenryB
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Well, all networks are subnets, and all subnets are networks; it's just words. Unless you cling to the Class A, Class B, Class C categorization it's really fairly meaningless. And if you are going to consider networks in terms of Classes....
I realize that these things are very important in college courses but in the real world, if you are dealing with non-routable, private address ranges, it really doesn't matter. There are far more addresses available than you could possibly need. So it's easier just to forget subnets and think in terms of one Class A network, 16 contiguous Class B networks, and 256 contiguous Class C networks. Which ones to use depends upon your needs.
I realize that these things are very important in college courses but in the real world, if you are dealing with non-routable, private address ranges, it really doesn't matter. There are far more addresses available than you could possibly need. So it's easier just to forget subnets and think in terms of one Class A network, 16 contiguous Class B networks, and 256 contiguous Class C networks. Which ones to use depends upon your needs.
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