Other than not being able to claim any more IP addresses in a subnet, what other bad things happen when a subnet reaches 100% utilization, if anything?

  • 5
    Total protonic reversal! Commented May 25, 2017 at 19:53
  • IP doesn't care whether an address is used or not - as far as the computer is concerned, subnet utilization might as well be a made up concept. Commented May 25, 2017 at 21:32
  • Whatever you do, just don't put a hub on that subnet. Not that hubs are really used anymore. But maybe you work for the Government, then it's possible--one see's the craziest stuff when working for the Government :)
    – Jeff.Clark
    Commented May 26, 2017 at 8:51
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    Is there a particular reason for all the sarcastic/humouristic comments? The guy asks a perfectly sensible question. Sure, the answer might be obvious to us, but not to everybody. Is it so hard to say "except for no more addresses being available, nothing bad happens" and leave it at that?
    – AnoE
    Commented May 26, 2017 at 11:21

1 Answer 1


A subnet (network) is really just a collection of contiguous addresses within a binary mask. It is simply a logical way to divide address block. If you run out of addresses in a network (subnet), then you are simply out of addresses in that network. Adding any more hosts would require reclaiming unused addresses, expanding the network (may not be possible), or adding a new network (requires a router to communicate between networks).

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    Okay. That's what I thought, but since I'm relatively new to the networking arena I wanted to make sure there weren't other consequences that could happen that I was unaware of. Thanks! Commented May 25, 2017 at 19:12
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    What happens if the subnet which fills up is or ::/0 ? ;-) Commented May 26, 2017 at 2:18
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    @TessellatingHeckler Then you invent IPv6
    – JBentley
    Commented May 26, 2017 at 10:04
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    @HagenvonEitzen, from a a practical standpoint, you would not be able to have a single network (LAN) with the over two billion hosts hosts on it that would be required to fill a /1 network. Aside from the cost, there is the matter of space required, and the fact that a broadcast network would collapse long before reaching that many hosts. Even with matchbox-sized (two cubic inches) devices, you are looking at over 70,000 cubic meters of devices, which must have power and cooling that requires more space, and most LAN protocols will not work over those types of distances.
    – Ron Maupin
    Commented May 26, 2017 at 14:40
  • 2
    FYI: Most dhcp servers in routers handle this by ignoring dhcp requests from new devices
    – Ferrybig
    Commented May 30, 2017 at 15:06

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