Mirjam Kühne

Returning Unannounced Legacy IPv4 Address Space

Mirjam Kühne
Contributors: Xavier Le Bris
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In the early days of the Internet, many organisations received very large amounts of address space. Some of it has not been used and is not visible on the Internet. As the RIPE NCC's pool of available IPv4 address space nears depletion, we are actively encouraging holders of unused unannounced space to return it.


When the American Registry for Internet Numbers (ARIN) was formed in December 1997, it inherited the InterNIC database of distributed IPv4 addresses and Autonomous System Numbers (ASNs) and the responsibility to maintain the records in it. These records became known as "early registrations" (or legacy address space).

After consultations with the RIR communities, it was decided that the interests of early registration resource holders would be best served by having the resources administered by the RIR operating in the region where the resources were used. This led to the Early Registrations Transfer (ERX) project in which early registrations were moved from the InterNIC database to RIR databases in various regions.

Returning Legacy Space

The RIPE NCC frequently receives unused IPv4 address space back for various reasons:

  • To be a good internet citizen
  • Companies stopped their business
  • Merger/acquisition of networks
  • Organisation realises addresses are not needed anymore

Recently, the RIPE NCC looked through all early registration addresses to see if they are visible (routed) on the Internet. We found that roughly 730 /16s of IPv4 address space held by 400 organisations are not visible on the global routing table.

This month, we are contacting legacy resource holders with unannounced IPv4 address space to ask if they would consider returning the unused space. Doing so is not only an act of goodwill towards the Internet community, but it can also provide a great publicity opportunity. Returning unused legacy space can also reduce the possibility of it being hijacked by illegitimate users who may use it  for a range of unsavoury activities.

We will report about the progress of receiving unused address space here on RIPE Labs.



This article is a contribution by Xavier Le Bris.

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About the author

Mirjam Kühne Based in Amsterdam, The Netherlands

I wrote the articles collected here during my time as community builder of the RIPE NCC and the maintainer and editor of RIPE Labs. I have since taken on a new role serving as the Chair of the RIPE Community. You can reach my new profile via the website link below.

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