We have been assigned a block of 64 IP's by ARIN (/26). We have a private range that is a /22. Every time we get a new block of public IP's we NAT them to the next available addresses in that range, so no new private subnets being made for this new /26 block.

My question is: how many will be usable by hosts? Normally I'd say 61 (1 for network, 1 for gateway, 1 for broadcast) but with a public block not sure.

  • to have someone properly answer this question you must include details about the amount of users/services/etc. Also, this is probably a better question for chat since it is opinion-oriented. If you are able to provide services and approx # of hosts I will gladly answer with the math that i would recommend Commented Dec 9, 2013 at 17:09
  • Those details aren't necessary at all. It's simple: 64 public IP's from ARIN, how many are usable/NATable and why?
    – A L
    Commented Dec 9, 2013 at 17:11
  • 2
    This is still worded as an opinion-based question, please revise it. Your question is akin to "i have a /24, what ip do i give my router and how many do i assign to hosts?" If your question is simply asking how many of the 64 addresses do you have the CAPABILITY to nat, that is a different question than what you have asked. Commented Dec 9, 2013 at 17:25
  • Edited for clarity, I was asking about capability. I included a bit more context as well. Thanks for your help!
    – A L
    Commented Dec 9, 2013 at 17:37
  • 3
    This still really hinges on the equipment in use and how the network is designed. This could be all of them, or it could be 61, 59, etc.
    – YLearn
    Commented Dec 9, 2013 at 18:08

1 Answer 1


IP addresses are IP addresses are IP addresses. Until (and unless!) you end up with an assignment of IP addresses in an ethernet (or ethernet-like) network, there is no concept of "network address" "broadcast address" and the like.

NAT functions are not "an ethernet(-like) network", so all IP addresses in a block like that are usable in a NAT configuration.

There's a very strong argument to be made for not setting NAT configurations up like that, though. If you're just mapping one set of IP addresses up as 1-1 NAT mappings to another "private" (air-quotes intended) set of IP addresses, then why not just assign the public addresses directly onto the systems and eliminate the NAT altogether?

  • Hey Jeff, thanks for a clear answer. As far as why they're not assigned directly to the boxes I couldn't say as I'm not directly involved with those decisions, I just saw the ticket on our end and the discussion along the same line and it made me wonder :)
    – A L
    Commented Dec 11, 2013 at 16:24

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.