For my education

We are having a little bit of FTTP cable laying and new connection chambers fitted around here.
My question is concerning CGNAT as by reading reading Thinkbroadband forums one or two alnets use this system:-
1 How does affect me if I went with isp who used it.
2 If needed can this be changed by user or bypassed.
3 Do openreach use this system

Edited by merrymouse (Sun 29-Jan-23 10:43:35)

Openreach just provide the connection and transport to the CP. what happens after that is down to the ISP. Not aware of any ISP using openreach that utilises CgNAT but there could be.

In reply to a post by merrymouse:

1 How does affect me if I went with isp who used it.

If the ISP only supplies IPv4 then you can't have random incoming connections. If they provide IPv6 as well generally it means you have to use v6 for anything unsolicated inbound. (e.g. port forwarding for games, or IP cameras)

2 If needed can this be changed by user or bypassed.

No it happens because there are not enough IPv4 addresses left. The ISPs don't want to do this.

3 Do openreach use this system

No, not Openreach, nor Cityfibre as these are network operators. Some network operators are also ISPs such as Hyperoptic, but most ISP choose a network such as Openreach or CF.

Some network operators such as Toob (building in my town), like Hyperoptic, only have one ISP but Toob are forming alliances with CityFibre so may offer other ISPs in future.

Edited by jchamier (Sun 29-Jan-23 12:17:44)

i thought we would have gone to IPv6 by now, but still very few providers use it, even Zzoomm a brand new, high-tech provider don't. I think they use CGNAT.

2 If needed can this be changed by user or bypassed.

One option is to use a VPN or L2TP tunnel to give you externally visible static IPv4 and IPv6 addresses.
I use AAISPs L2TP service - although it is limited to 200Mbps (not too much of a restriction).
A big advantage is that I can swap between my FTTP and 4G broadband fallback, and the addresses just stay the same.

In reply to a post by zyborg47:

i thought we would have gone to IPv6 by now, but still very few providers use it, even Zzoomm a brand new, high-tech provider don't. I think they use CGNAT.

There are large parts of the internet that are only accessible over IPv6, but mostly not in english, so UK/USA providers haven't cared. On mobile only EE provides IPv6, and backwards compatible routing for v4 over v6. Their competitors haven't bothered !


The likes of Virgin Media and Plusnet are way behind, as BT, EE, and Sky prove. That Zzoomm can't do it means they just haven't recruited the right network trained staff as they are in full control. I would avoid a CGNAT only provider, unless they have a cheap add-on option of a static public IPv4.

Otherwise you are stuck with having to buy a third party service such as AAISP's L2TP.

Edited by jchamier (Sun 29-Jan-23 13:57:04)

Thank you all for the replies. everything is clearer now and I shall be going down the path as outlined by jchamier if we get an isp who uses this system. At the moment fibre is in its early days around here. One alnet is fitting chambers to connect to openreach ducts and openreach have pulled there cable through.

Further to what jchamier said, I doubt if Plusnet use CGNAT, but I haven't investigated. However what I have done is see if they still offer a single static IP address on home products at about the lowest cost, a £5 one-off payment. It looks like they do, but it would be wise to check if you are considering them and they choose to supply FTTP to your area.

In reply to a post by pluralist:

Further to what jchamier said, I doubt if Plusnet use CGNAT, but I haven't investigated

As an older ISP they do not, they claim to have sufficient IPv4 addresses, and as part of BT group they can probably work with other allocations.

The main issues are for the newer ISPs whom aren't part of a much older, larger business.

Exactly my thoughts re Plusnet, hence the "I doubt if" .