There are some substantial differences between 4G and wired residential networks, which can complicate the use of DDNS to directly access remote devices.
Dynamic DNS (DDNS) allows consistent access to a known domain by updating with the external IP address of the network, which often changes in residential networks. It is used by millions of our customers in both home environments and as integral components of distributed commercial applications.
In parts of the world — rural areas and regions with a developing internet — it is more common to utilize phone-based systems such as 4G networks to access the internet. So it makes sense that those users would look to DDNS for remote access just like they would if they were on a normal, wired residential network.
This article will explore the differences between 4G and wired residential networks, and explain what that means for DDNS usage.
How Dynamic DNS works
With a normal broadband or fiber line in a residential network, there is a one-to-one relationship between the external IP address and the network being accessed. The router typically utilizes DHCP from there to assign internal IP addresses, but fundamentally that external IP refers to you. Your neighbor across the street will have a different external IP from you. Because there is a 1:1 relationship with the IP, you could actually make a request just to that IP address and access the resource (assuming you configure your network to do so):
Example request without DNS: http://220.127.116.11/catpic
The issue DDNS solves is that, unless you have paid your internet service provider for a static IP, the specific IP assigned to your router will change periodically. If you don’t know what the new IP is, you will not be able to find where your network is to access it.
DDNS runs an agent, usually either on the router itself or on a device on the network, that periodically checks the external IP address and adds this IP address to a DNS host. Instead of you making the request to the IP address directly, you make the request to a DNS name, which resolves to the current IP of your network. This way it is always current. Our request now looks like this:
Example request with DNS: http://myhomeserver.example.com/catpic
The last step in the process is to configure port forwarding within your network such that a request on, say, port 80 is routed to the internal IP of your web server, port 88 is routed to your CCTV device, port 8080 is routed to your printer, etc. This allows you to get the request to the device you intend.
Visually, this whole process looks something like this:
DDNS issues on 4G
Telephone networks work a little differently than normal residential networks, however. Instead of a one-to-one relationship between the external IP address and your own network, your personal device is hidden within the 4G network.
This means that your cellphone or other connected device is operating on a private IP. If you tried to connect to the external IP address trying to access content on your cellphone, the cell tower would not understand where to send the request, because there are thousands of possible devices for that IP.
If you do happen to set up DDNS on a remote device using 4G, as in the illustration above, you will get one of two outcomes. Either the update client will take the external IP of the cell tower, or, less commonly, it will use the private IP address of your remote device. In either result, you will not be able to connect to your remote device.
In rare cases, providers may allow you to create a port forwarding tunnel within the telephone network. Just as we established port forwarding in our own network in the first example, this approach would pass traffic inside the private network of the operator to your remote device. But this is very much the exception to the rule.
With 4G and other phone-based networks, you must check with your provider to see if they provide port forwarding within their network to utilize DDNS to access your remote device.