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Changing your internet service provider can be one of the most daunting tasks that a network administrator can carry out. The primary concern being the loss of email traffic while the change is propagating around the internet.

However with some careful planning and actions carried out well in advance of the actual switch, you can make the change almost transparent.

This is a sample plan which deals with ensuring that no email is lost or web hits go astray. While it may go over the top in some areas, these actions almost ensure that no traffic is lost, nor email delayed in any way. 

Important - don't attempt the switch to the new ISP the day the new ISP is installed. Make sure that everything is working before you try any changes. Get the new IP addresses and decide what you are doing with them.
Ask the new ISP to configure Reverse DNS on the new IP addresses as required.

Name Server Change

If you are also changing name servers then you should get everything setup with the new ISP before the change. As you haven't made the change to their name servers yet, the Internet will not use the new name server information.
However this may impact the ISPs ability to email you, so you may want to use old information until you are ready to switch, then change tot he new information just before you change.

One Week before the switch

1. Setup an account with a dynamic DNS provider and create two hosts. Point one host at your current MX record IP address, and the other at your current web site hosting address.
2. Ask your current ISP to cut the TTL (Time to Live) period to the minimum that they will support.
3. Wait for those changes to take effect around the internet and then test.

At Lease three days before the switch

Add the dynamic DNS mail host as an additional MX record to your live domain - so that you have two MX records listed.

Change your web host to use an alias for the host www and point it at the dynamic DNS host you created earlier.

Day of the Switch

Just before you move your hardware over to the new ISP, go to the old ISP and change the IP address for your current MX record host (mail.domain.com or whatever) to the new IP address. This means that anyone who hits the old name servers will get the new information.

Then switch your hardware across, and change your name servers as appropriate.

After the Switch

Once the switch is complete (minutes after changing the hardware across) you can then change the www address to the new IP address and enter the correct IP address in to your master MX record with your new ISP. Leave the dynamic DNS host in place for at least three days to allow for data replication to take place.

Three Days Later

Once you are sure that everything is using the new records, remove the dynamic DNS hosts from your records and terminate the old ISP.

Why Use a Dynamic DNS Provider?

A dynamic DNS provider will have the IP address change is live in about 15 minutes. Therefore by having the dynamic DNS name on the DNS records at both the new and old ISP, you don't need to wait very long for the change to propagate round.

Separate Services

Many of these issues can be made simpler by separating the services.

• An ISP who provides just your internet connection
• A web host who provides just your web site
• A domain name registrar who looks after your domain name and external facing name server.

Unfortunately the ISP and web hosting companies don't like that approach as they prefer to have control over your domain name. In many cases the web hosting companies like you to transfer your domain name to them.

There are no technical reasons why this change must be carried out - it is pure business reasons. They can then hold your domain name to ransom in the event that you want to change your web hosting company, or be awkward about making the change.

Your company domain name is usually one its most prized assets, so you need to take steps to protect it.

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