PlusNet Tests IP Address-Sharing As IPv6 Fails To Take Off

PlusNet, the Sheffield-based ISP owned by BT, is testing a controversial scheme in which all its customers could share one IP address through Carrier Grade NAT (CGNAT). The move, made necessary by the slow progress of the new protocol IPv6, could limit customers’ Internet actions and cause problems with tracking abuse or criminal action.

IP addresses were never meant to be shared but the current version of the Internet protocol (IPv4) does not allow enough different addresses to go around. A new version of the protocol (IPv6) with vastly more addresses, has been ready for use for the last 20 years but has been implemented disastrously slowly. In December, the UK’s IPv6 promotion body 6UK closed down in despair, and CGNAT is widely lamented as an admission of IPv6’s ongoing failure.

IPv4 addresses have been shared for many years: most home networks and business networks hide their complexity behind a single gateway connected to the Internet, with a single IP address. The gateway uses network address translation (NAT), to translate between addresses on the local network and those on the wider Internet so that, for instance, each person sees the web pages and emails they ask for.

Now that the last few blocks of IPv4 addresses have been issued, bigger groups are having to share and PlusNet is applying NAT at the service provider level, sharing one IP address between all its users, which will have to go through a network translator box buried in PlusNet’s network, to access any services on the Internet.

PlusNet does the maths

Critics have said that this will mean users cannot host content within PlusNet and it could cause problems with any end-to-end Internet services. PlusNet’s Matt Taylor defended the decision in a forum posting, saying: “Carrier Grade NAT (CGNAT) is similar to the NAT that people use on their home routers. For most people they will never notice, most mobile operators already use CGNAT and so most applications will just work.”

Despite PlusNet’s efforts to reassure users, this is ringing alarm bells with some. It is true that mobile operators have adopted CGNAT, because they have connected many millions of users in an era when IPv4 addresses have been growing scarce. ISP Review points out that these mobile operators “are notorious for being very restrictive and that’s often in stark contrast to the otherwise flexible nature of fixed line internet connectivity”.

In its defence, PlusNet points out that users would find IPv6 addresses did not suit them: “Even if the world switched on IPv6 today, there would still be people and applications that don’t work under IPv6, some games consoles, for example. As such everyone will still need an IPv4 address for the foreseeable future.”

ISPs will have to operate a “dual stack” approach, supporting both protocols, but this is made difficult by the shortage of IPv4 addresses, so some sort of sharing is inevitable, PlusNet argued.

Just testing

The ISP also said this is just a test for now: “We’re just about to test and evaluate a CGNAT system to see if it’s suitable and see what kind of applications and services work and don’t work, as such we’d like a bit of help from people to try out and see. We’re doing testing internally too but with so many devices, applications, games, VPNs, etcetera, we’ll never test everything.

Volunteer testers will get a special username and are being asked to “do what you would normally do” and record what works and what does not. If they find CGNAT does not support things they need, they will be allowed to switch back to non-CGNAT addresses.

“It wouldn’t surprise me if this became common among bigger/cheaper ISPs,” said ISP Review’s Mark Jackson. “We view it as controversial because of the potential for a poor implementation of CGNAT, which would leave consumers with a distinctly less-flexible, fixed-line broadband service and yet they’d probably still end up paying the same as they do today.”

Ironically, PlusNet’s parent BT has a very large stock of IPv4 addresses and is unlikely to adopt CGNAT any time soon.

The PlusNet team did not give specifics on when the trial would start but it should kick off towards the end of the month and last for three weeks.

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