What is Dynamic DNS ? – Why Use Dynamic DNS Services?

dynamic-dnsDynamic DNS keeps DNS records automatically up to date when an IP address changes.

Dynamic DNS is used in large networks that host internal services, and use their own internal DNS and DHCP servers.

However small companies, and home networks don’t normally have their own DNS server so why would they need Dynamic DNS ?

Why Use Dynamic DNS Services?

Dynamic DNS Services are used by small companies and individuals when they want to publish a service on the Internet, and it is hosted within an internal network that uses a NAT router to connect to the internet.

In the following discussion we are going to assume that we want to make a web server located on an internal server available on the internet.

The  network diagram below shows the configuration


The Internal IP address is assigned to the internal server by the NAT router, but usually in these circumstances we will give it a static internal IP address.

To make the web service available on the internet we use a technique called port forwarding ( see the  port forwarding  and Internal vs external IP address articles for details).

Now our web server appears to our external client to be located at IPex and on port Portex.

If we put some typical numbers into this we will see our web server at

Ip Address= and on Port 80

All we need now do is to tell our external client to use these values.

However the external IP address IPex ( may also be dynamically assigned by the ISP, and we cannot make it static unless we pay for a static address.

In addition, the external client has to remember the IP address.

If we now introduce a Dynamic DNS service into the picture.

With Dynamic DNS  we assign the web server a name which we can then give to external clients. –This name is fixed.

We then assign the external IP address to the name.

Now because this external IP address will change periodically we will need to update the  DNS record periodically.

We could of course do this manually, but that would be very unreliable.

Instead the ability to update the DNS server records is built into most NAT routers.

Here is a screen shot of the Dynamic DNS configuration page of my NAT router (BT Home Hub).


The configuration involves entering the name of your DDNS provider and your login details.

So before you can enable Dynamic  DNS you will need an account from a DDNS provider. The main providers all work in a similar way and the registration process is simple.

Below is the sign-up form for the NO-IP Dynamic DNS service.


Dynamic DNS (DDNS) Not Supported!

If your router doesn’t support DDNS updates you can get a DDNS client that you install on a machine that does the same job.

The only problem with this approach is that the machine needs to be constantly running.

Dynamic DNS (DDNS) Video

Here is a video that covers the above:

Common Uses

Although it is used by gamers and tech Geeks it is probably going to see more widespread adoption in remote security/surveillance and control areas.


Dynamic DNS (DDNS) is very useful if you need to access internal network services from across the Internet.

It isn’t designed for hosting a business website, for that you will need standard web hosting.

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