Private use of non-RFC1918 IP space

Skywing Skywing at
Mon Feb 2 16:14:54 UTC 2009

If you get an address reservation from a registry, then you could certainly use that space in a way that doesn't entail globally-reachable routing.  In fact, IIRC one of the RFCs explicitly mentions this possibility in the event that overlapping private use address space usage makes interconnection between two networks otherwise unworkable.

However, as everyone else had assumed you might be doing, "borrowing" unassigned or assigned-to-someone-else (for which all "unassigned" can eventually be expected to devolve into) is unwise.

– S

-----Original Message-----
From: Trey Darley <trey at>
Sent: Monday, February 02, 2009 07:48
To: nanog at <nanog at>
Subject: Private use of non-RFC1918 IP space

Hi, y'all -

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 be very interested in corresponding off-list with anyone who's in a
similar position.

Kingfisher Operations
Trey Darley - Principal

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