I'm trying to set a CNAME record (www) at ISP-A to forward to a subdomain at ISP-B.

the domain/website at ISP-A works flawlessly at ISP-A, the website at the subdomain at ISP-B works also good. but the CNAME (www) doesn't. It shows an (automatic) page from ISP-B that they can't find the domain.

ISP-B states that it doesn't work because the website is located at a cluster which uses a shared IP-address. I'm not a DNS-guru, but the DNS redirects to the subdomain, not an IP-address. So having a shared IP or not is irrelevant.

Am I correct in saying that ISP-B is trying to get me to push my domain to them (at a significant premium I must add.)? Or is it completely fair what they are saying and am I just being stupid?

  • A CNAME will point a subdomain (in this case, your www) at another domain name. It doesn't have anything to do with the IP of that domain name, that is a separate resolution in the DNS process (An A record presumably). The CNAME record is only responsible for getting you to the other record. – MaQleod May 14 '14 at 17:02
up vote 2 down vote accepted

ISP-B is using virtual hosting to route requests.

Your IP and port is shared so your host can only separate requests to different sites by using the URL sent by the client. They are only serving your site when a client asks for the domain you have registered to them.

Your browser will request the URL that you have entered in address bar regardless of the CNAME. That URL isn't registered in ISP-B so they won't route the request to your site.

Surely ISP-B can serve any request that is sent to their server. However, users requesting for arbitrary virtual domain names may not make too much sense to the host. I don't think this kind of service is available anywhere.

  • 1
    thus the browser is requesting a URL that isn't hosted at ISP-B and thus not present in their virtual-host, therefore the request/URL cannot be correctly routed. Thanks! – puredevotion May 14 '14 at 18:49
  • 1
    Right. I appended the conclusion to the answer :) – Mikuz May 14 '14 at 18:58
  • @puredevotion I'd also like to add that a host can, of course, route any incoming requests. They just won't do it (for quite legitimate reasons). – Mikuz May 14 '14 at 19:32

Imagine the DNS looks like this:

isp-a.domain.com.   A  10.10.10.10
www.isp-a.domain.com. CNAME isp-a.domain.com.
isp-b.domain.com. A 20.20.20.20     
www.isp-b.domain.com. CNAME ipa-b.domain.com.

assuming isp-b.domain.com resolves to YOUR website, the cname will work regardless of the IP.

with it being shared, perhaps your issue is that port 80/443 is in use, in which case you could run your site on 8080 or something. then you use the same dns setup and specify the port when you browse to it.


If you are limited by a host's DNS, can you host your DNS offsite to control it yourself? there are multiple options for free dns hosting and paid for dns hosting.

  • yes, although i have no access to that on ISP-B (SaaS-like service). but both A-records resolve, and it seems like CNAME records are being catched in order to coax business – puredevotion May 14 '14 at 18:30

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