Server Fault is a question and answer site for system and network administrators. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

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?

share|improve this question
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 '12 at 20:00
You might want to add a Nagios check for "whois". :) – Gerald Combs Jun 7 '12 at 20:03
Follow-up: the range has been assigned to GOOGLE! – Pablo Montepagano Feb 22 '14 at 22:22
up vote 4 down vote accepted

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.

share|improve this answer

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.

share|improve this answer

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.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

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