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I have a client that created over 600+ websites whose DNS records point to an actual IP address and not name servers. They are looking to move from their current host and do not want to lose their IP address. If the IP address has to be changed, then it would need to be changed in the DNS records of all 600+ sites.

Is there a way to keep the IP address when transferring to another host?

Is there a work-around that they can use to avoid manually changing all the sites?

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    I don't follow this. Exactly what did they do to their DNS records? Give a clear example. – Michael Hampton Aug 14 '14 at 17:48
  • My client is a web host affiliate. They host websites on their servers. Instead of making their nameservers mynamesever.com they only use IP addresses. When my client gains a new customer, they point their (www.mycompany.com) to 10.127.12.4 instead of mynameserver.com. They have done this over 600+ times. For domains that they registered it would be no big deal, but some of their clients registered their domains with another host and had to update their own DNS records to point to this IP. Every customer's nameservers point to an IP not a host name. – Sharron Denice Aug 14 '14 at 17:54
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    Changing 600 DNS records would take about 0.9 seconds using a script and then the time it takes for TTL and name servers to update. Why is this unacceptable? – SpacemanSpiff Aug 14 '14 at 17:55
  • And clarify what is moving, the nameserver or the webhost. – SpacemanSpiff Aug 14 '14 at 17:56
  • @SpacemanSpiff but for about 75% of their customers? They had their own domain and its not on an accessible server. For the domains that they host it wouldn't be much of a problem. But for the rest? I can't think of a logical solution. – Sharron Denice Aug 14 '14 at 17:57
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First of all, you cannot bring the IP address along as you move to another hosting provider. IP addresses can only be moved between hosting providers, if you have a block of addresses, which was large enough to be announced over BGP.

Any approach you take to moving would require a transition period where you are using one IP at the current hosting provider and one IP at the new hosting provider.

If you are hosting only the website and not DNS for the clients, then the clients will have to update their DNS records, wherever they are hosted. For subdomains, this could be avoided, if the customer was using a CNAME record. The CNAME record has a tiny additional overhead to look up, but that is rarely significant. A CNAME record could be used for www.example.com, but it would not work for example.com itself, since it would have to be the only record, and example.com would have a NS record and possibly MX record as well.

So in that situation there is really no way around coordinating the transition with the customers.

If you were hosting DNS for your customers as well, they could have their NS records point to names inside your own domain. That way they don't need any glue, and their domain will have no IP addresses other than on the DNS servers you host for them. As with the CNAME records, this has a tiny additional overhead.

This approach however does require you to host their entire DNS zone, and you would have to be hosting it at two or more different hosting providers to provide high availability.

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Your assumption that pointing a "nameserver" for a domain to an IP address is correct. Porting the IP over while "possible" does not sound like you meet the requirements to achieve this.

You need to do this in stages. The first of which is getting the nameserver for each domain pointed to a DNS record which resolves to the same IP address they use today. There should be no impact for doing this. Then you'll stand up a new DNS server that will deliver the same responses, and update the DNS record from the old server to the new. You'll just have to be diligent and trust in the data you do have, thats all you can do.

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In AIX you can use IP Alias to solve this. Let say you current IP address is 10.5.1.98 and your new IP address is 90.4.12.67 then you can define the 10.5.1.98 as an alias on top of 90.4.12.67. This way any server referencing the IP address 10.5.1.98 would be forwarded to 90.4.12.67 automatically. Whatever flavor of UNIX you are using or Linux for that matter, you have to Google on that flavor with IP aliasing to find if you can implement it. I know I am posting several months later to when this question was asked. This way anyone looking for a similar solution would have some ideas on how to deal with it.

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    This doesn't work if you're going to be moving to a different AS. Heck, it doesn't work if you're moving to a different broadcast domain. Honestly, I can't think of a case in which this would be a reasonable solution. – Hyppy Apr 19 '15 at 17:57

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