While attempting to host a business website an issue has developed, the business has an exchange server pointed to from the current ISP via a telecom MAX record entry?, and we had hoped to edit the A record with the new ISP IP address. What are the potential risk having two ISP’s, 1 pointer for email server and 1 for their website using the same domain.
I’m not sure I understand your question correctly.
First of all, an A record is an Alias record; it must reflect back to a C (Canonical) record. So when you say you’re going to edit the A record, I assume you mean you’re going to have it point back to a different C record.
As for the issues, it’s a recommended practice to have multiple DNS servers (or any other kind, for that matter) for redundancy. You’ll have to make one a master and any others as slaves, then set up domain transfers to keep them all in sync.
There are lots of free resources for how to do this on the web, but if you’re going to be doing a lot of DNS administration, I highly recommend the O’Reilly book by by Albitz and Liu – absolutely worth every penny.
Is this setup running on Windows 2003 Small Business Server or Windows 2008 Business Essential Server?
the easiest way to do this if it is not is to have 2 IP addresses one for your www. record and one for your A record and MX Record
To do this, have your DNS provider go in and do the following:
1. Change your www record to 192.168.1.100 (or whatever your IP address block is) so that when you ping your domain: domain.com it responds from 192.168.1.100
make sure you note this change in your firewall and make a rule for all your Port 80 (Web) to this IP address.
2. Have your service provider change your A Record for 192.168.1.101 and have the alias become mail.domain.com and then have the DNS provider make mail.domain.com as your MX record. Make sure all port 25 traffic is pointed to this IP address as well as your internal exchange server.
Most firewalls are able to create virtual IP interfaces. So this will make it easier for you to have multiple internet facing IP addresses within the same firewall on the same physical interface.
This will tell your DNS Server(s) that when a user requests http://www.domain.com to point to 192.168.100 and when a user sends mail to user@domain.com that the mail server is located at 192.168.1.101
Your question is a bit vague, so here are my assumptions. The business in question has their external DNS hosted by their ISP. There is currently an A record that associates the name of the mail server with the mail server’s public IP address. In turn, there is an MX record that points to the mail server’s A record. That would be pretty standard. Now you want to add a public web server that is hosted by a different provider? Well, wherever it is doesn’t really matter. You just create another A record (at the current ISP) that associates the name of the web server (let’s call it http://www.company.com) with the corresponding IP address. In the end, you’d end up with something like this
A mail.company.com 12.111.224.3
MX 10 mail.company.com
A http://www.company.com 214.22.1.112
For the record, the first reply from molasses is incorrect. "A" records are not "alias" records, nor do they have to refer back to a canonical record (which is CNAME, not C in any case). "A" records are Address records and they simply associate a fully-qualified domain name, or FQDN, (like mail.company.com) with an IP address as shown above. A CNAME would come into play if you had multiple FQDNs that all referred to the same IP address. Rather than creating a bunch of different A records, you create one A record and several CNAME records. In your case, it’s unlike you will even need a CNAME record.