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Is there any particular reason as of why we should assign IP addresses to the largest subnet first? Could anyone give a simple example of why this is the better option?

Let's say I have two subnets: one for 40 hosts, and the second one for 4 hosts. How come that starting with the smaller subnet would cause a bigger waste of IPs? The hosts take the same number of IPs no matter what IPs were assigned to them.

user5539357
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  • Explain what you mean by "The hosts take the same number of IPs no matter what IPs were assigned to them." – lampwins Apr 07 '16 at 17:09
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide your own answer and accept it. – Ron Maupin Aug 07 '17 at 14:22

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I'll add to what @RonMaupin is trying to say by using this analogy. When you are packing the trunk of a car, you start by putting in the largest items first and make your way down to the smallest. In this way, the space in the trunk is optimized because the smaller objects can fit in the free space left behind from the putting the large objects in first. You can certainly start with the small objects, but you run the risk of running out of open space and will have to rip out everything and start over. By optimizing the space utilization from the start, you can more easily anticipate when you will run out of space. The same principal applies to subnetting.

lampwins
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It because you can't start the network for 40 hosts immediately after the network for four hosts.

If the network for four hosts is 10.0.0.0/29, the network for 40 hosts would need to start at 10.0.0.64/26. That means you have dead addresses from 10.0.0.8 to 10.0.0.63.

On the other hand, if the network for 40 hosts is 10.0.0.0/26, the network for 4 hosts can be 10.0.0.64/29, leaving no dead addresses in between.

Ron Maupin
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