Broadband News

IPv4 exhaustion leads to Relish using CGNAT

Relish has started to provide a fast broadband service in the parts of London where it is most needed in the last few months and its use of 4G LTE combined with a home router and scooter delivery is making it popular in the parts of London where people are finding it difficult to get good speeds.

One aspect of the service has recently come to light and that is that the service uses Carrier Grade NAT (CGNAT), as a way to share a limited number of IPv4 addresses between the users of a service. CGNAT is not new, in fact for mobile broadband it has been common for some years, and BT Consumer and PlusNet have both ran trials of CGNAT to evaluate it as a stop gap solution before more widespread IPv6 adoption takes place.

"Due to the global exhaustion of legacy IP addresses (IPv4) ISPs around the world have been forced to implement CGNAT solutions to enable a single IP address to be shared by many customers – this is becoming increasingly common.

We have implemented a solution used by many network operators and ISPs for fixed and mobile services. This was tested extensively prior to launch using a range of applications including online gaming with no issues reported. We do acknowledge that it is difficult to test every scenario that may exist in every application and as a result we are going to release a block of public IPv4 addresses to our consumer customers. This will be subject to some qualifying criteria and an additional monthly fee. These will be available from the 1st September via our customer care teams.

As a longer-term solution we are implementing a project to allow customers to use IPv6 addressing."

Will Harnden – Marketing Director

The vast majority of broadband users are not going to be aware of CGNAT and while NAT on consumer routers can break some applications the carrier grade version is much better at ensuring problematic protocols are handled sensibly.

The news that Relish is working on a paid option for people to have a public IPv4 address is welcome and may make life easier for some home workers and offices where the Relish wireless router has replaced their fixed broadband. Of course long term once IPv6 is more widely adopted this problem of limited IP ranges goes away.

The 4G LTE service sold by Relish is advertised as up to 50 Mbps and certainly we are seeing people getting those sorts of speeds, below is a comparison of the median speeds for Relish users compared to all other broadband connections in the three London Boroughs where most of the Relish coverage is located.

Speed test results for Relish compared to everyone else
Authority Relish Median Download Speed Relish top 25% percentile Download Relish Median Upload Speed Others Median Download Others top 25% percentile Download Others Median Upload
Tower Hamlets London Borough 16.8 Mbps 27.3 Mbps 3.3 Mbps 15.4 Mbps 32.2 Mbps 1.2 Mbps
City of Westminster 21.5 Mbps 35.9 Mbps 1.2 Mbps 13 Mbps 25.3 Mbps 1 Mbps
City and County of the City of London 17.7 Mbps 23.2 Mbps 3 Mbps 14.7 Mbps 38.9 Mbps 2.7 Mbps
Combined London Region
(Others figures top 25% is high from Virgin Media and FTTC coverage in the suburbs of Greater London)
18.9 Mbps 23.6 Mbps 2.1 Mbps 21.5 Mbps 47.7 Mbps 2.7 Mbps
NOTE: Relish is available outside the three named Boroughs but not enough data was available to make a comparison, hence the combined London Region.

The figures may not look too exciting to those who regularly see 60 to 100 Mbps speeds every day, but without the tie to a fixed landline and unlimited usage which is hard to find via mobile 4G tethering they have a sizeable market and impossible for £20/month. The focus in London has been the slow speeds in the City of London and Relish do offer a real opportunity to get speeds well beyond those that people with long ADSL2+ lines as their only option can currently get.

We have been chasing this story for a week or so and hope to have pricing information soon on public IPv4 addressing and have improved the auto detection of Relish customers on our speed test so that more results can appear on our maps and in our data analysis.

Update Friday 29th August We have been informed that the price for a static public IPv4 address will be £10/month. The testing of IPv6 addresses is underway and we believe we have seen some of these tests on our speed tester too since Relish launched.

Obviously £10 per month for an IPv4 address may seem a lot but when the basic service is £20 per month with no voice line rental payment needed, the total price is still not unreasonable particularly as download and upload speeds from fixed line services are so patchy in areas like Westminster and the City of London.


What we need is an EU regulation that ISP's are not allowed to use CGNAT unless they also offer IPv6 as well. Unless someone actually twists the arms of ISP's then the majority are not going to sort out offering IPv6.

  • jabuzzard
  • over 6 years ago

One thing that disappoints me about Plusnet is that after running a beta program they seem to have given up on IPv6. Most ISPs just don't seem to care.

  • AndrueC
  • over 6 years ago

This was a deal breaker for someone I know. 30Meg v under 2Meg for little more money seems good, but without any ability to make inbound connections it really is only half a service.

  • Desmond
  • over 6 years ago

Google recently announced that web pages that support SSL will get a higher ranking. I hope they extended that to ipv6 in the future.

  • FlappySocks
  • over 6 years ago

Can someone explain to me how this would work? Would it make online gaming unworkable?

  • Ultraman1966
  • over 6 years ago

There definitely will be some unexpected consequences, that will cause problems for some. Specialist applications. Homeworkers etc.

It's such a shame so many ISPs & hosts don't support ipv6. It's just not in the spirit of the internet. In the past, an ISP would add ipv6, simply because they could. Now there is no excuse, because all routers support it now, at least at the commercial level.

I would avoid any ISP that has compulsory GNAT. And personally I would avoid any ISP that doesn't have IPV6, or at least roadmap towards it.

At least has ipv6. Kudos for that.

  • FlappySocks
  • over 6 years ago

CGNAT is common in many ISPs outside the UK. Most modern VPNs used by homeworkers operate across it fine. Those who want to allow inbound connections typically have to pay more - as Relish seem to be doing.

  • AlderPoint
  • over 6 years ago

AndrueC plusnet have a new trial on ipv6 running right now, I am one of the trialists, although I agree isps are dragging their feet waaaay too much on ipv6. I also agree that ipv6 needs a regulation push.

  • chrysalis
  • over 6 years ago

until bt, talktalk(as most resellers use talktalk),sky and Virgin media do it none of the others will bother with IPV6

  • leexgx
  • over 6 years ago

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