DDNS Over 4G

If you use a standard 4G mobile broadband SIM card in your 4G router then you will be unable to use Dynamic DNS.  This is becuase 4G mobile network providers in the UK use Carrier Grade NAT (CGNAT) which means that your 4G SIM connection is allocated a PRIVATE IP address on the mobile networks private network.

So if you have a PC connected to your 4G Router and visit www.showmyip.co.uk then the IP address you will see will be a public IP address belonging to the mobile network and your SIM card connection will be sitting behind this public IP address along with 250 other devices all with private IP addresses.

therefore in order to get connected to YOUR device you would need to contact your mobile provider and ask them to remove the other 249 customers sharing that public IP address and port forward the public IP to your private IP – good luck with that!

The way around this is to just use a 4G Fixed IP SIM card – there are many reliable fixed IP SIM card providers in the UK that will be able to provide a service to enable easy and reliable connectivity to your 4G Router.

If you don’t want to use a fixed IP SIM provider then your only other option is to use a three mobile SIM card and use the APN of 3internet and configure your router to connect at 3G only.  This way, when your router connects to the Three mobile 3G service it will request a public IP address and if there are any available then your connection will be allocated a public IP address and you will be able to use DDNS.  However this is not a contracted service from 3mobile and may be stopped at any time and in some cases your connection will not be allocated a public IP address so your DDND will not work.

How to get your router working with a three mobile SIM

Remember this is not a guaranteed solution and you will not always be allocated a PUBLIC IP ADDRESS so DDNS will not always work.  A Public IP address on your 3Mobile SIM card is not a contracted part of your 3mobile service and may be withdrawn at any time.

This 3mobile connection will only work when using 3G – if you use the APN of 3internet and connect at 4G then you will only be allocated a private IP address which means that DDNS will not work.

Some IP camera suppliers will tell you that they have a portal that allows you to connect to your Camera without any form of DDNS or for your router to have a PUBLIC IP Address – however – for these types of solutions that we have checked for our customers the camera provider is just providing a DDNS service and are not providing a magic portal – so you will still need to know the PUBLIC IP address of your router – so your 3G router will need a Fixed IP SIM card or you will need to use a 3mobile SIM as described above – however if you are using the cheap option of a standard 3mobile SIM card you MUST REMEMBER that your router will not always be allocated a public IP address from 3mobile so your DDNS solution will not work.

The easy way to test this is to connect a PC directly to the router and visit www.showmyip.co.uk and this will tell you the PUBLIC IP address of your 3G connection and then attempt to connect to this IP address from a computer connected to a different internet connection eg. your office internet – if you can connect to the public IP address shown on www.showmyip.co.uk then it means that 3mobile have provided your connection with a public IP address – if you can’t connect to it then it means that 3mobile have only provided you with a PRIVATE IP so no method of DDNS will work – even the one supplied by your IP camera manufacturer.


Q: Will DDNS work with a eSIM Router?

A: It will depend on whether 3mobile, who are the only network to provide a public IP address with their mobile broadband service (don’t forget it is not guaranteed and may be withdrawn at any time) so it will depend on whether they has an esim service that can be used with your eSIM router.