Using public address space for private networking is a gross misuse of the resource.
No it is not. IP was invented to enable internetworking. The IPv4 address registry was set up so that anyone who wanted to use IP for internetworking could get unique addresses. The key here, is internetworking, which refers to exchanging packets with other networks. It is possible to internetwork without ever exchanging packets with the public Internet.
Go to any registry and ask for address space for your private networking that you do not intend to announce to the internet. They will laugh at you, and point you to RFC1918. (and likely flag you as someone to whom address space should never be assigned.)
Not true. Two of my former employers went to ARIN every year or two and received blocks around a /16 in size, specifically for use on global IP networks that did not intend to ever announce those addresses on the Internet. There are several other companies which operate somewhat similar networks. Also, "announce to the Internet" doesn't mean what you think it does. First of all there is no Internet to announce to, only peers, There are a lot of smaller networks which do announce routes to a small number of regional peers, but those routes are NOT transitively announced to the rest of the public Internet. These networks *ARE* connected to the Internet, but you won't see their routes in any of the major views (routeviews, ris, etc) which are considered as the global routing table.
The only reason legacy holders get away with such crap is because there's no clear contract governing their assignment.
All of the companies that I am aware of who get RIR addresses with no intention of announcing it on the Internet, are paid up members in good standing of one or more RIRs. Legacy holders really don't play in this game except for the DOD.
First off, someone will have to do a lot more than 5 minutes of poking router-servers to see just how sparsely used ("announced") the space really is. That includes digging through BGP histories to see if it's ever been announced. Then research who should be in control of the space (announced or not.) Then send out nasty sounding letters informing whomever that X address space has not been announced to the public internet in Y years; on Z date, the space will reenter the IANA/ICANN free pool for reassignment. (cue lawyers :-)) They'd also be highly motivated to return unused space if they were being billing for it.
First of all, tools like RIPE's RIS make checking BGP history child's play. Secondly, you left out the court cases where the companies all get injunctions against ARIN because ARIN did regularly give them addresses under ARIN policy and nothing has changed to justify pulling the addresses back. These addresses are in use, i.e. configured in devices that provide a commercial internetworking service with packets flowing 24 hours a day. --Michael Dillon