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Dynamic DNS

If you are unfortunate enough to have a broadband connection with a dynamic IP address, then you will need to use a dynamic DNS service to maintain the current IP address for your host name. Even if your service provider keeps changing your IP address, you will have the same address all the time.

Having a fixed name, instead dynamic number makes using services such as email services and remote access to your own machine.

With the increasing popularity of permanent internet connects using broadband, Dynamic DNS services have become widespread (check the Google Directory listing linked below).

What is DNS?

DNS stands for Domain Name System. Think of it like a phone book. Every machine on the internet has a number like 85.234.131.89. You could browse the web this way, (try it) but you cannot know every number - there are thousands. Instead you can type in a more friendly name, in this case http://www.sembee.info/  . When you type in the name, your machine goes to already defined name servers, looks up the name and gets the IP address. If the local server doesn't know the address, then it passes the request to the next server in the chain.

Once it has the address it can connect to that server and you are browsing the web. As long as you know the address of the name servers, then you can look up the address - in much the same way that you know the number for directory enquires for the telephone.

When you connect to the internet using a standard dial up modem in most cases you are given a dynamically assigned IP address. This changes each time you connect. With a cable modem or other permanent internet connection you are given an IP address in much the same way (unless you have paid for a fixed IP address) except you will typically have it for longer. However the address will change. This is where a Dynamic DNS service comes in.

A more detailed, non technical explanation of domain names can be found on Internic's web site. (opens new window)

What is a Dynamic DNS solution?

Dynamic DNS allows you to keep another server informed of what your IP address is all the time. When it changes, the server has to be updated and then you can continue using it. It allows you to run services that need a fixed IP address, like mail servers.

The updates can be carried out in two ways, either manually (you go to the web site and enter the IP address) or automatically using an agent. The automatic solution is best if you have a machine connected to the Internet permanently. If you address changes while you are away from the computer, then it is automatically updated.

Choosing a Solution

If you type Dynamic DNS in to search engine then you will find there are quite a few services available. Some you pay for, some you don't. A good place to start would be Google's directory:
http://directory.google.com/Top/Computers/Internet/Protocols/DNS/DNS_Providers/Dynamic_DNS/  
You will need to evaluate each service individually and see whether you need to pay for each service. It will depend on what you are looking to achieve with the service.

Keeping it Up to Date

Once you are using a Dynamic DNS solution then you need to keep it up to date. This is carried out using an agent. This needs to be installed on a machine that is on all the time so that it can monitor your connection for any changes to the address. There are many agents available, some are free, some need to be paid for, depending on the complexity of the client. Check the site of the provider you have chosen for information on these agents. Your router may also have an update tool built in to it.

Working with a Domain Name

With most Dynamic DNS service providers, you have three ways of using their service:

1. Use a sub domain of one their domain names - usually free of charge
2. Use your own domain name - there is usually a charge for this.
3. Mapping a CNAME in your own domain on the host name provided.

Depending on whether you have registered a domain name will depend on how which option you want to use.

If you opt for the first two options, you will make the changes on their systems. To use the third option, you will need an address from the provider (host.dynamic.com for example) then you would put a CNAME so that mail.yourdomain.com resolves to host.dynamic.com. 

Email
If you are using a domain name provided by your Dynamic DNS provider, then you shouldn't need to change your email settings, as you probably not be using that domain for email. If you are, then you probably know enough about domain and DNS management to be able to set it up yourself.

If you are using your own registered domain name, then things can look complicated.
If your domain name company (who registered your domain) is providing email services, just set your MX (email server) records on your Dynamic DNS back to their servers. Email will continue to flow, and their system will accept email for it.
If you are hosting your own server, then ensure that the MX records are set to the full dynamic DNS host name.
You can run Exchange on a dynamic IP address, which we have written about elsewhere on this site.

Web
In a similar way to email, you should just created a new pointer on your Dynamic DNS service to your existing web space. Again - if you are doing something different with web then you probably don't need this advice.
Either way, it is probably a better idea to use a commercial host rather than host your own web space as it leaves someone else to worry about the security of the server.

Domain Registration

If you don't have a domain name, and would like to get register one to use with a Dynamic DNS service, then one that we have used with great success is http://DomainsForExchange.net/ .
They provide the flexibility to allow you to configure your domain and email so that it works as outlined above.  

Other Ideas
Once you have your Dynamic DNS name running, then you can use it for anything, such as remote control or terminal services. The service is just for name resolution. After the name has been resolved no other data goes through the Dynamic DNS organisation. If it runs on the internet then you can use it with Dynamic DNS.

Using with your LAN

If you are on a LAN, then resolution of the Dynamic DNS name may not work or even give the wrong address.  If you have an internal DNS server, for example because you are using Active Directory, then you need to create a single host zone. If you do not have an internal DNS server then you will need to put a hosts file on each machine with the local network address instead. However this can cause problems with laptop users who roam, so you should use an internal DNS server if possible. 

Links:
Google's Dynamic DNS Section:
http://directory.google.com/Top/Computers/Software/Internet/Servers/Address_Management/Dynamic_DNS_Services/

Another Explanation of Dynamic DNS: http://www.technopagan.org/dynamic/