I've been administrating an office network that was set up by someone else and I always found this weird about it:

Their internal subnet is in this range: It's been working fine, but it does not conform with RFC 1918.

I've been trying to find out who has IPs in the range, but a simple WHOIS only shows that they "belong" to ARIN. Could it be that they're simply unassigned? I tried ICMP pinging a wide range of them and got no response...

I guess I'll eventually change the subnet to something more standard, but it's a curious thing, don't you think?

  • Ignoring the ip address range that is currently in use: private networks don't have to conform to RFC 1918. It's slightly unorthodox but it's not wrong to not use RFC 1918 ip addresses internally.
    – joeqwerty
    Jun 7, 2012 at 20:00
  • 1
    You might want to add a Nagios check for "whois". :) Jun 7, 2012 at 20:03
  • Follow-up: the range has been assigned to GOOGLE!
    – Pablo M
    Feb 22, 2014 at 22:22

3 Answers 3


No, it's not a valid private subnet, as you can seen in the RFC. You've most likely not had issues because of the use of NAT when hitting the Internet. In which case, you would only run into issues if you were trying to access something using that range.

You should take the time to correct the subnet to avoid any future problems.


Someday ARIN may allocate 172.253.x.y to somebody.

There are two sides to it, it will take effort to migrate away from your current configuration, and how likely is it that you will want to connect to that somebody.

But on the other hand, it will be a pain to troubleshoot, and resolve on short notice if you do want to connect.


The subnet does not appear to be assigned (yet), but is not reserved for private use, as you already pointed out. You may want to switch it sometime soon before the address' are allocated.

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