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Plusnet in trial of carrier grade NAT to conserve IPv4 addresses
Tuesday 15 January 2013 10:38:56 by Andrew Ferguson

The prediction that one day we will run out of IPv4 addresses is often seen as a warning with little substance to it, and many providers appear to see little point in implementing IPv6 at this time. The predictions though may becoming true, as Plusnet moves to start a Carrier Grade NAT trial, to help conserve the number of IPv4 addresses they need.

"We need a bit of help with some testing over the next few weeks. 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."

Plusnet seeking customers to trial carrier grade NAT

Carrier Grade NAT has been used by mobile operators in the past, and the result for ADSL and fibre connections is that the router in the home would be handed a private network IP address. This creates several problems (1) services that rely on port forwarding/UPnP will not work (2) if the private IP range is the same as routers LAN side this can cause routing issues (3) services like VPN that use a public IP for security checks may fail.

"All ISPs should be providing proper IPv6 first, and using NAT purely as a stop-gap. This will allow innovation to continue and use the end to end design of IP, and it will mean services using IPv6 will 'just work'.

At AAISP we have been providing IPv6 for over 10 years now, and we expect to be able to provide at the very least a single fixed IPv4 address per line without carrier grade NAT for many years to come."

Comment from Adrian Kennard of AAISP

Hopefully Plusnet will implement IPv6 swiftly, the BT Wholesale platform supports dual stack IPv4 and IPv6 connections already. None of the major broadband providers in the UK support IPv6 yet, and while there is no compelling IPv6 application as yet, by starting to switch now the providers can avoid a big confusing rush in a couple of years.

One of the common problems for the consumer is that some hardware, particularly current generation games consoles do not support IPv6, if the next generation consoles do then the problems of configuring NAT may at last be consigned to history, but only if broadband providers support IPv6.

A slight chicken and egg situation does exist and that is support for IPv6 in consumer routers, but the situation is improving and the buying power of the larger providers will quickly change that.

Update 4pm: Adrian Kennard has written a longer blog article going into greater depth about the problems carrier grade NAT can introduce.


Posted by ionic over 4 years ago
Hopefullt Plusnet will implement their CGN using the shared address space detailed in rather than private IP space. This will mitigate problem (2) above.

Offering a static translation (where you're always NATed out on the same public address which may be shared with others) may help (3) also.

If it breaks p2p uploads a bit, it might help with the bandwidth hogs on their new unlimited tarriffs too...

Posted by wellhiddenmark over 4 years ago
This is 'get what you pay for' Internet access. Pay little, get little. I'm sure it's fine for people who want nothing more than an 'essentials' connection for web browsing and e-mail. A bold welcome to the 'tiered' internet. Static translation will be 'fun' when the few IPv4 addresses NATed out get blocked for spam / abuse, however spurious the reason. Serious P2P users would have to pay extra for a seedbox.
Posted by mabibby over 4 years ago
Sensible measure I think....

The majority of customers who just want to surf the net won't be affected by a CGN.

Gives a good price break tiering I think to the more hardcore users.

Using a CGN will also increase security and put the task with PlusNET, as no inbound attacks will route back to a single ADSL client.
Posted by speculatrix over 4 years ago
To Adrian K: there is a compelling IPv6 application, it's called Google, who offer many of their services on IPv6 already. We just need them to announce they're turning off IPv4 on some services to get people focussed.
Posted by -Alex- over 4 years ago
It's disappointing that an ISP is trialling CGN before finishing IPv6 deployment to their customers.
Posted by Tanaka71 over 4 years ago
@speculatrix You cant expect google to do that. You cant expect any supplier to do that.

How about charging for ipv4 addresses, which gradually goes up every year. ISP's a with a lot of users would save money by switching users to ipv6 (and tunnel ipv4 NAT). End users can always pay extra to have ipv4.
Posted by camieabz over 4 years ago
How do ISPs monitor/track usage and or illegal practices if many share one public address?

Posted by camieabz over 4 years ago
Sorry, another thought.

Does the contention ratios change or remain the same if CGN is in force?
Posted by chrysalis over 4 years ago
so they as expected left ipv6 too late, germany is already rolling out dual stack to customers, and we have carrier grade nat? fail!!!
Posted by zyborg47 over 4 years ago
tThe one problem is how many routers/modems can cope with IPv6? I know none of my ADSl routers. Not sure about the cable modem, i saw something about IPv6, but not really took any notice.
Posted by Tanaka71 over 4 years ago
I have a Chrome plugin, that shows me when a site I am looking at is ipv6. Loads of sites are these days, including this one.

Beggars belief Plusnet are talking CGN, and haven't even got ipv6 running!
Posted by oliver341 over 4 years ago
The danger is that ISPs use CGN to extend the life of IPv4. They then consider issuing dedicated IPv4 addresses on a paid-for basis, a bit like static IP addresses with some companies now.

It's not a solution I'd welcome, but since ISPs are so slow with IPv6 roll out, you start to wonder if they just want to find an IPv4 solution such as this and forget about IPv6 altogether.
Posted by chrysalis over 4 years ago
routers can support ipv6 with a firmware upgrade, its a fairly simple process to rollout firmware updates to isp supplied routers and to update ones not shipped out yet. Routers is a non issue since router vendors follow what the market demands, if ipv6 is supplied by the isp then retail routers will support and also vendors will alter firmwares as isps dictate.
Posted by chrysalis over 4 years ago
olivier exactly my point, they seem to just be fighting of ipv6, and also possibly using it as a money spinner. we dont really know how many ip's the likes of plusnet have left.
Posted by chrysalis over 4 years ago
I think the government needs to step in, regulate the likes of CGN can only be used if ipv6 is in active deployment, in other words enforce it. Run out of ips and no ipv6? then no new customers until you get act together.
Posted by KarlAustin over 4 years ago
No really, we do not need the govt. mandating anything in terms of the internet and how networks are deployed. What we need from the govt. is them mandating that all new contracts for IT services/systems must be fully IPv6 functional like they did in the USA.
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