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UK ISP BT Quietly Forces CGNAT IPv4 Internet Address Sharing Pilot

Posted Friday, May 3rd, 2013 (1:06 pm) by Mark Jackson (Score 4,538)
ipv6 internet address

Customers of BT Retail’s Total Broadband Option 1 package have reportedly become experimental subjects for the ISP’s new pilot of the controversial IPv4 internet address sharing (Carrier Grade NAT) technology, which could cause problems because it allows a single IP address to be shared between several users.

Most fixed line ISPs assign a unique Internet Protocol (IP) address to your connection each time you go online via the IPv4 (Internet Protocol version 4) standard. Sadly these addresses are running out and its replacement, IPv6, is not directly compatible with the old standard.

As a result ISPs will need to run dual-stack networks, which allow both the IPv4 and IPv6 standards to communicate, although this also means that IPv4 addresses are still likely to be needed for quite a few years to come.

Meanwhile the number of spare IPv4’s is still in decline and many ISPs are expected to solve this by adopting CGNAT to help share the remaining IPv4 addresses (much as mobile broadband operators already do). ISPreview.co.uk wrote a fairly extensive article about all this in January 2013 – The Dangers of Adopting IPv4 Internet Address Sharing.

BTRetail Statement on CGNAT (Thinkbroadband)

We have decided that we will pilot this new technology with our Option 1 Total Broadband customers who on average use the internet least. We believe they are the least likely group of customers to experience any issues or disruptions due to CGNAT, which can interfere with complex online activities like hosting servers at home. We do not think these customers will notice any difference at all in their broadband performance, but if any of these customers did have any resulting issues, we would be happy to restore their connection to an individual IP address.

BT is also working to introduce IPv6 internet addresses during 2013, but customers will need both IPv4 and IPv6 addresses for the foreseeable future.”

BT specifically states that “certain” customers will find that they could be sharing a single IP address with up to nine other users, although happily those who wish to opt-out of the seemingly enforced pilot can do so by visiting their related CGNAT FAQ Page and filling-in an opt-out form (you might well wish to do this).

The ISP claims to be “confident that you’ll not notice any impact to the reliability, speed, privacy or security of your BT Broadband service“, although it immediately contradicts this a few lines later by saying, “some applications, such as online games, VPNs, file transfer (FTP) or dynamic DNS services … may have problems” (note to BT: online multiplayer games are pretty popular).

One problem is that some internet services, such as those mentioned above (or other things like web-polls and online authentication systems), assume that every user will have a unique IP address and this can cause problems for those who don’t. For example, if somebody “sharing” you IP is banned from a service then you too could end up suffering from the same restriction. Port forwarding on your router, which is often needed for some online games and other services, can also run into difficulties with CGNAT.

In reality this may be a problem that ISPs, especially the big boys, cannot easily avoid and indeed most have already expressed a desire to adopt this solution. As a result internet providers are putting a lot of effort into ensuring that their chosen method does not disrupt services for existing customers, although some problems may be unavoidable. Check out our above linked article for more detail and extended feedback from ISPs.

In an ideal world ISPs might offer a special non-CGNAT service for customers, such as online gamers, who want to be able to use the internet as it was intended. At least BT has, for now, had the good sense to give their customers an opt-out solution.

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14 Responses
  1. Kyle

    I’ve been wondering whether this forced adoption is lawful… Surely such a significant change (albeit not visible) would have to enter a phase of consulation (at least 30 days) with customers?

    It just feels wrong to push this upon customers and I very much doubt that Option 1 customers would fall into the same ‘savvy’ category as some of the top-tier packages, thus questioning their ability to opt-out — if, indeed, they are even informed.

  2. DanielM

    I have been using it on plusnet for some time now. not seen many problems, VPN works fine.

  3. Alan

    If PlusNet are using the same standard as BT, then as DanielM are saying, it shouldn’t have any problems with VPN – BT’s implementation appears to be based on RFC6598 and is issuing 100.64/10 IP addresses, so should be well out of the way of any VPN / corporate network ranges, unless some Network Admin somewhere has decided to use the ‘Shared Address Space’ range in the wrong way. (the full RFC can be viewed at http://tools.ietf.org/html/rfc6598)

  4. zemadeiran

    This is all good and well but how are the mafiaa going to track down who was behind which ip and at what time when several users are reachable by the same public ip?

    Not to mention the impact this will have on Ben Dover’s pocket…

  5. x66yh

    Mobile phones already use CGNAT so I think that the issues of identifying the particular phone/modem/router whatever downloading stuff or issues re accessing online banking within a CGNAT environment have been well sorted out.

    • DanielM

      Only some.. not all

      Three depends what APN you use.
      T-Mobile uses public IP’s
      Orange use NAT
      Vodafone use NAT
      O2 Use NAT
      EE uses NAT

    • Ignitionnet

      T-Mobile do not use public IPs for phones. Mine reports 10.x addresses when connected to T-Mobile, always has.

    • DanielM

      Strange i have only seen the 10 range twice in the last 14 days or so

      it’s usually 178, 31,

      it also depends on your plan. pay as you go never seem to get the 10. range

  6. cyclope

    @zemadeiran: I think that the use of P2P applications may be problematic,or non pssible, with CGN as like a hell of a lot of apps, it requires ports to be fowarded,something that CGN breaks, So they would save bandwith too,Plus online gaming would suffer too,CGN will break theinternet for most in some shape or form, ISP CGN can only be a bad thing (unless you only browse the web and use e-mail)
    @DanielM: Plusnet as far as im aware ran a short trial of CGN some time ago, they have also unlike BT trialed IPv6 too in the past, And according to a member of their support staff, they had no plans to roll CGN out and time soon ( as per info given during April 13)

    • DanielM

      well the trial is still active so it aint short.

      to confirm my ip starts with 100.127.254

  7. cyclope

    Did you opt in for the trial, from what i can gather it was unlike BT, where a customer had to opt in for the trial ?

  8. x66yh

    Yes,
    You opted into the trial on Plusnet.
    Plusnet advertised on their forums for volunteers.
    Being part of a trial you were expected to help out, try out things see what worked and what didn’t and report back.
    You got a seperate login different from your normal one.

    The majority of BT’s retail customers will indeed only do email and browse the web

  9. Richard

    Would it be possible to run IP4 NAT behind an IP6 home router? So domestic users who are used to NAT in their homes keep seeing 192.168 range addresses, but the outside world uses IP6? You can encapsulate IP4 destinations in IP6 addresses so older machines will be able to reach their favourite IP4 web sites, but over time more and more will rely on IP6.

    • Tony

      Yes, it’s called 4rd

      Once an ISP has transitioned to an ipv6 network the routers will provide ipv4 connectivity for legacy devices, tunneling over the ipv6 network so that those devices can still see ipv4 websites.

      Basically the inverse of the way it commonly works at the moment.

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