Private use of non-RFC1918 IP space

Seth Mattinen sethm at
Mon Feb 2 22:24:20 UTC 2009

Stephen Sprunk wrote:
> Trey Darley 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.
> "Closed" networks nearly always end up getting connected to public 
> networks, either by intent or by accident.  If you act as if your 
> network will remain "closed" forever, e.g. by using public addresses 
> that are (or will be) assigned to someone else, you're going to cause a 
> lot of headaches for yourself or your replacement down the road, 
> eventually.
> Contrary to popular belief, ARIN (and possibly other RIRs) _will_ assign 
> public IPs for private/closed networks if you can explain why RFC1918 
> space will not suffice for your needs, e.g. because you are running a 
> private internetwork between multiple companies and thus NAT/RFC1918 is 
> simply not viable due to the number of ASes and the difficulty in 
> avoiding collisions or the sheer number of hosts...

Or you can always get some PA space from an ISP rather easily.


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