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Status of Legacy IPv4 Address Space

Xavier Le Bris — 12 Sep 2011
Last year, we described how we were actively encouraging holders of unused or unannounced IPv4 address space to return it. In this article we report on the responses we have received.

In Returning Unannounced Legacy IPv4 Address Space we described how the RIPE NCC is reaching out to holders of unannounced legacy address space. The RIPE NCC actively worked to improve records of legacy address space by contacting the resource holders of /16s or more that were not announced in the global routing table.

A bulk email was sent to the 400 organisation email contacts. We asked these resource holders to consider returning this address space if it was not used .

Of the 400 emails we sent, 186 addresses bounced. For many of them we found other contact information. However, 95 of them remained unreachable.Below you can find a chart showing the type of responses we received.

Below you can find a number of reactions and responses we received so far:

  • 160 address holders updated the information in the RIPE Database.
  • 126 address holders confirmed that the addresses were used internally (prior to the existence of RFC1918 private address space).
  • 95 ERX holders were unreachable and/or did not exist anymore.
  • 84 address holders moved the resources into registry systems (either by becoming an LIR or by being a customer of an LIR).
  • 16 address holders returned the address space to the RIPE NCC
  • 3 address holders started announcing the prefix after we contacted them


Unannounced Legacy IPv4 Address Space


It was often very difficult and time consuming to get in contact with legacy address space holders.  A lot of information were out of date.  However, we can conclude that this activity showed some positive results: A big chunk of IPv4 address space was returned into the free pool of addresses. For another big portion, the registration information in the RIPE Database is now up to date.




Nicholas Shanks says:
04 Apr, 2013 01:16 PM
Can you post a follow-up to this follow-up, with 2013 data? Also, please name and shame organisations which: (1) were originally unreachable and have still not updated their contact information, (2) have not renumbered to RFC1918 space in the more than 13 years they have had to do so, or transferred to an LIR.
Mirjam Kühne says:
05 Apr, 2013 02:46 PM
Hi Nicholas,

Contacting holders of unannounced legacy address space was a one-time project. This is because these holders are under no obligation to return their address space to the RIRs - it was only as an act of goodwill to the Internet community that some chose to do so.

The RIPE NCC helps legacy resource holders update their registration details in the RIPE Database on a daily basis. However, the RIPE NCC is unable to require that legacy holders keep their registration details accurate in the same way as it can with those who received their space from the RIPE NCC.

There is currently a proposal in the RIPE Policy Development Process (PDP) that relates to legacy Internet number resources. This can be found here:
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