Private use of non-RFC1918 IP space

Joe Greco jgreco at
Mon Feb 2 16:07:11 UTC 2009

> On Feb 2, 2009, at 10:57 AM, Jeffrey Ollie wrote:
> > On Mon, Feb 2, 2009 at 9:48 AM, Trey Darley <trey at>  
> > wrote:
> >>
> >> Some colleagues and I are running into a bit of a problem. We've been
> >> using RFC 1918 Class A space but due to the way subnets have been
> >> allocated we are pondering the use of public IP space. As the  
> >> network in
> >> question is strictly closed I don't anticipate any problems with  
> >> this as
> >> the addresses would be unambiguous within our environment. I'm  
> >> curious if
> >> anyone else is doing this.
> >
> > I'd recommend against it, because even though the network is not
> > connected to the Internet now you never know what the future holds.
> > Even if it's never connected there are always things that seem to pop
> > up and cause problems.
> >
> > Also, if you're address allocation policy has been so badly managed
> > that you've run out of space in adding more IPs to the pool
> > isn't going to help for very long.
> It will if you manage it better.
> Fortunately, there's a /12 and a /24 still left.

And a /16.  (What's the /24?)  And possibly some other space that is

> A /12 is more space  
> than 99.99% of the networks on the Internet need, so why wouldn't that  
> suffice instead of using "real" space.

If you absolutely, positively *had* to allocate another /8, it'd probably
be best to look through Class A space for networks that are not likely to
ever appear on the Internet.  ISTR a bunch of them are assigned to the US
military, for example.

... JG
Joe Greco - Network Services - Milwaukee, WI -
"We call it the 'one bite at the apple' rule. Give me one chance [and] then I
won't contact you again." - Direct Marketing Ass'n position on e-mail spam(CNN)
With 24 million small businesses in the US alone, that's way too many apples.

More information about the NANOG mailing list