Reclaiming unused IPv4 addresses

As many people might know, the number of IPv4 addresses is limited and almost all have been allocated (see here and here for more information).


Although CERN has been allocated some 340,000 addresses, the way these are allocated across the site is not as efficient as we would like. As we face an increasing demand for IPv4 addresses with the growth in virtual machines, the IT Department’s Communication Systems Group will be reorganising address allocation during 2016 to make more efficient use of the IPv4 address ranges that have been allocated to CERN. We aim, wherever possible, to avoid giving out fixed IP addresses, and have all devices connected to the campus network obtain an address dynamically each time they connect.

As a first stage, starting in February, IP addresses that have not been used for more than 9 months will be reclaimed. No information about the devices concerned will be deleted from LANDB, but a new IP address will have to be requested if they are ever reconnected to the network. Among other things, reclaiming these unused IP addresses will enable us to remove unused cable connections in the network starpoints, thus making space for the new cabling and switches we need to introduce campus-wide Wi-Fi services.

The second stage to reclaim IPv4 addresses will take place in the middle of the year when we move to a single range of dynamically allocated addresses for systems connected to the campus network. By replacing the two separate ranges allocated today (one for fixed addresses and one for portable devices), we can significantly reduce the total number of addresses that have to be reserved for campus devices, thus freeing up addresses that can be used for servers in the Computer Centre. More news about this second stage will be provided nearer the time, including information about how people can request a fixed IP address if necessary.

If you have any questions about these changes please contact the Service Desk who will follow up as necessary. Please note that systems connected to the Technical Network are not concerned by either of these changes.

by IT Department