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ISP PlusNet Trials Controversial IPv4 Address Sharing as IPv6 Alternative

Tuesday, January 15th, 2013 (9:04 am) - Score 6,004

UK ISP PlusNet has quietly announced a controversial plan to conduct a 3 week trial of IPv4 address sharing (Carrier Grade NAT). But sharing a single IP address between several customers, often as a means of delaying IPv6 adoption, carries with it more than a few problems.

Fixed line broadband ISPs typically assign a unique Internet Protocol (IP) address to your internet connection each time you go online, which enables you to communicate with other websites and online services. Sadly existing IPv4 addresses are running out and as a result ISPs only have a limited supply left, which will eventually leave them unable to add new connections unless they adopt its replacement, IPv6, or share some of their remaining IPv4 addresses.

Most ISPs are expected to solve this by adopting a dual-stack setup, which allows both old IPv4 and new IPv6 addresses to work alongside each other (otherwise neither standard is directly compatible with the other). But it could be years before IPv6 becomes the norm and in the meantime IPv4 addresses will still be needed.

Matt Taylor, Plusnet Support, said:

As many people will probably know there’s a finite number of IP addresses in the world and there aren’t many left. In order to ensure that people have access to the Internet during the transition to the new world of IPv6 ISPs like ourselves are looking at options including Carrier Grade NAT. 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.

Carrier Grade NAT (CGNAT) is similar to the NAT that people use on their home routers. The NAT on your home router lets all the devices on your network (PCs, tablets, phones, consoles etc.) share one IP address. What CGNAT does is take that a step further and has several customers sharing one IP address. For most people they will never notice, most mobile operators already use CGNAT and so most applications will just work. 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).”

It’s certainly true that Mobile Broadband operators have used IPv4 address sharing solutions for many years, yet mobile providers are also notorious for being very restrictive and that’s often in stark contrast to the otherwise flexible nature of fixed line internet connectivity.

The problems with sharing a single IP among several users are quite numerous. 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. 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.

On top of that customers would have difficulty when attempting to host their own FTP, website or game servers and port forwarding may not work properly either. The list goes on. Suffice to say that IP address sharing is a minefield of security, performance and connectivity concerns.

Matt Taylor added:

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, etc. we’ll never test everything. With some help we’ll try and get as much as we can.”

It’s interesting to note that PlusNet’s parent, BT, currently has a sizeable pool of spare IPv4 addresses and so we’d be surprised if they adopted address sharing anytime soon. At the same time some ISPs may consider address sharing to be a necessary evil, at least until the world goes completely IPv6 (we’re still a long way off that happening), which could in the future turn IPv4 supporting connections into a premium service. Hopefully most ISPs will be better prepared than that and should have enough IPv4s’ to last a few more years but nothing is certain.

PlusNet’s trial is expected to get underway towards the end of January 2013 and will last for three weeks; thanks to the BE Usergroup for pointing this development out. Any readers wishing to get a bit more background on the problem of IPv4 depletion and IPv6 adoption should check out our recent article on the subject – Big UK ISPs Respond to IPv6 Readiness Fears.

Leave a Comment
15 Responses
  1. Neil McRae says:

    why is it controversial? Everyone ISP will have to do this.

  2. Mark Jackson says:

    It remains to be seen whether every ISP will have to do it, in fact we known quite a few that expect they won’t. It’s controversial due to all of the potential drawbacks mentioned above, which could impede the flexibility of fixed line broadband connectivity.

    Had IPv6 adoption begun earlier then such measures might never have been needed.

    1. Neil McRae says:

      > Had IPv6 adoption begun earlier then such measures might never have been needed.

      “Aye, and if my grandmother had wheels, she’d be a wagon.”

  3. Neil McRae says:

    At the rate of growth we have plus the lack of movement to V4 for huge numbers of applications – every ISP will have to do some type of CGNAT or other gateway-ing technology at some stage.

    most people already run V4 nat to connect their home network to their ISP hence why I question why its so “controversial”.


    1. Mark Jackson says:

      It wouldn’t surprise me if this became common among bigger / cheaper ISPs, although as the MD of AAISP said last July 2012: “The hope is that we can always provide every customer with at least one fixed public external IPv4 address. We think we have enough IPv4 addresses to do that in the long term and never have to deploy carrier grade NAT. But it is hard to predict the future“.

      We’ve seen those thoughts echoed by a fair number of smaller ISPs, which could at least give some of them a stronger selling point going forward (hence my remark about “premium” services).

      Never the less 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.

      Certainly if your “grandmother had wheels, she’d be a wagon” but that’s no excuse. The entire industry, from ISPs to hardware manufacturers, has had years and years to prepare but for the most part it didn’t.

    2. FibreFred says:

      Its controversial because it breaks things, Xbox Live for example. With an standard ipv4 public address you can have an Open NAT (important) with a carrier grade NAT’d private ip address your NAT will be strict (booo)

      Just one example, it will affect all online gaming

      This stuff is fine for browsing, email etc etc but no good for gamers

  4. Karen says:

    Take something like Xbox live. It requires the ability to route to your xbox from external. uPnP made this a lot easier so most people didn’t have to worry. Something like CGNat is going to make it a lot harder for people to run such things.

  5. John says:

    Something tells me that in the future, much like we pay extra for dedicated IP addresses, they’ll put the majority of users who will never notice on shared CGNAT and having your own IP4 address will be an extra fee.

    1. Stoat says:

      If you bite the bullet and move to IPv6, address space congestion isn’t an issue.

      All these “solutions” are increasingly intrusive (and expensive) heath-robinson ways of keeping IPv4 going instead of just firing up IPv6 stacks.

  6. Corrado Mella says:

    I find CGNAT an acceptable compromise, a necessary evil we’ll have to face, sooner or later.

    Why not to leave the “cheap and cheerful” providers for the masses like PlusNet to do CGNAT, and other providers “for the most discerning customers” to get you your own public IPv4 IP?

    Not to say that the “privilege” to have your own fixed IPv4 IP should lead to a heavy premium price to pay, but most of internet users just want to browse and get email don’t even contemplate gaming, let alone running their own servers…

    I have another idea that might get us out of the woods for good.

    All the authorities that assigned IPv4 blocks should assess if they are being properly used, and demand them to be put back in the pool if they aren’t.

    I have on good authority that some early adopters and big players are holding onto entire pools of A classes and using them very little, if at all,or using them to assign an IP to the computer on the desk of their employees – with all the stupid security risks involved and requiring heavy countermeasures a good NAT could solve for good.

    Can I suggest a use it or lose it policy?

    Apart those assigned to ISPs to dynamic ranges or to provision connections, others that don’t do should justify their allocation.

    I would allow not more than a 10% of unused addresses in their allocation as spares and room for growth.

    I’m sure this policy would single handedly:
    find and recover a large number of IPv4 addresses allocated but unused, pushing requirement for CGNAT in the future – if ever;
    – save those (involuntary?) hoarders a few quid;
    – stop in their tracks those that are holding onto their IPv4 allocation to make that an IPv$ / IPv€ allocation (curiously both symbols are on the “4” key on UK keyboards!) to re-sell on the grey/black market to people desperate for an IPv4 address when we really are out of them.

    After all, public IP addresses are just that, public – as in public property, not something belonging to anybody. Why would us – collectively – allow a public or private entity to hold onto some public resources without use or justification? We wouldn’t allow this to be for anything else, why are we allowing this for IPv4 addresses?

    Your IPv4 address pool: Use it or lose it!

    1. FibreFred says:

      And what what your use it or loose it approach achieve? Surely it would just push the move to ipv6 further into the long grass?

    2. Corrado Mella says:

      As always FibreFred doesn’t get it. Is it a lack of literacy, dyslexia, brain cells…?

      “Use it or Lose it” means that whole class A (/8) IP ranges assigned ages ago to companies like IBM, HP, Digital (now HP), AT&T (x2), Xerox, Apple, Ford, Halliburton, Nortel, Prudential, DuPont, Merck can be redeployed each into 256 smaller B (/16) or 65536 (256*256) C (/24) classes IP ranges, handing back to the previous assignees just the class they need (B or C).

      Every A class contains 16’777’216 (sixteen million seven hundred seventiseven thousand two hundred and sixteen!) IP addresses, WTF does IBM do with 16’777’216 IP addresses??? In fact, WHO ON EARTH needs 16’777’216 IP addresses allocated exclusively to them?

      Look here and despair.

      That’s A LOT of addresses wasted brought back to use, and will keep us going for years and years, while IPv6 comes online gently and quietly. No last minute rush.

      I’m even considering if IPv6 is really necessary, once we’ve brought back to good use all this waste. But shhhh… we need a paradigm shift so HP, IBM, and all these shameless resource hoarders can sell us new shiny IPv6 enabled trinkets.

      Come on, who’s on board? Let’s get’em!

  7. Agrajag says:

    You touched on the problem of IPs being banned from certain places, but what about unlawful file sharing? As we know, IP tracing is the only real way to track it, and if Neil McRae is correct in saying that all ISPs will have to adopt IP sharing, then wouldn’t this effectively take away the only weapon against unlawful file sharing?

    1. Mark Jackson says:

      No as even mobile operators can still track such activity back to a specific connection, even if the IP is shared. But it is harder and more costly to achieve.

  8. Michael says:

    “…If the internet did ‘go pop’, then I’m quietly confident we’d be one of the providers that came out on top. We’ve invested a lot of time and money into our broadband network….”
    With not enough IPv4 addresses for the customer base and no investment in IPv6 im not sure how that fantasy would be made true.

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