Plusnet to share customer IP addresses


Yorkshire ISP Plusnet is to trial a system which would share IP addresses among subscribers in a bid to avert a shortage in IPv4 addresses.

The move has been made as the number of IPv4 is all but used up and IPv6, which would have solved the problem, hasn't taken off in the UK as planned.

The three week trial will see volunteer customers sharing IPv4 addresses instead of having their own. The trial uses Carrier Grade Network Address Translation (CGNAT).

Mobile operators already use CGNAT and so most applications will just work.

CGNAT is a system similar to the NAT that customers use on home routers. NAT on a router allows all devices behind it to use the same IP address. CGNAT takes this one stage further and allows several customers to us the same internet-facing IP address.

Volunteers will get a special username and will be asked to use their internet connection as normal. They will also have to record what works and what doesn't. Should CGNAT fail to support applications they need (such as port forwarding and content hosting), users would be allowed to switch back to normal connectivity.

"For most people they will never notice, most mobile operators already use CGNAT and so most applications will just work," said Matt Taylor of Plusnet Support.

"The main problem is where you are hosting services on your broadband connection like hosting a website or hosting games (the kind of thing for which you set up port forwarding on your router)."

Mark Jackson of ISP Review said that the new system may well become the norm among larger ISPs, but warned that there were problems with such implementations.

"For example, you might find it difficult to access some online games or services if another person is already using the same service via your IP," he said.

"Similarly if an individual with your IP is banned from sending email or accessing a particular website then you too would be affected. Likewise if somebody downloaded child abuse pictures on your IP.. you get the idea."

Jackson noted that Plusnet's parent company BT had a surplus of IP addresses and said it would be unlikely that it would follow suit any time soon.

The trial gets underway at the end of the month and will last around three weeks.

Rene Millman

Rene Millman is a freelance writer and broadcaster who covers cybersecurity, AI, IoT, and the cloud. He also works as a contributing analyst at GigaOm and has previously worked as an analyst for Gartner covering the infrastructure market. He has made numerous television appearances to give his views and expertise on technology trends and companies that affect and shape our lives. You can follow Rene Millman on Twitter.