There are times when you will need to have multiple IP addresses on a server. It could be for an additional receive connector in Exchange, or for another website in IIS, among other things. This is not recommended if the server is a domain controller and/or DNS server. Best practice for a DC/DNS server is to have a single NIC (or NIC team) with a single IP address. Having more than one IP can and does cause DNS resolution issues, logon issues for clients, and other Active Directory weirdness. However, I realize that there are situations where you don’t have any other way of accomplishing an objective, and you simply must have multiple IPs on your DC/DNS server. I have been IN that situation more than once, which is the reason for this post.
Adding another IP address on a server can be accomplished either by adding a secondary IP address on an existing network adapter (shown above), or by adding another network adapter with its own IP address.
In any case, by default, the server will register all assigned IP addresses in DNS. This may cause problems if clients resolve an IP for the server other than the one they need to access whatever service they are trying to use. For example, if you have multiple IP addresses on an Exchange server, but only the first IP address bound to the default receive connector, clients running Outlook that were given the secondary IP address by DNS would have trouble connecting to Exchange.
There are several ways to prevent registration of multiple IP addresses in DNS, depending on the configuration (secondary IP or NIC) and role of your server.
Scenario 1: Windows Server with multiple network adapters; no secondary IP addresses on either adapter, nor is the server a DNS server.
Resolution: In this situation, the only action you should need to take is to prevent the server from registering the address from the 2nd NIC. You can do that by going to the properties of the connection –> IPv4 settings –> Advanced button –> DNS tab. Then, UNcheck the “Register this connection’s addresses in DNS” checkbox, as shown here:
Scenario 2: Windows Server with multiple network adapters running DNS server role.
Resolution: First, perform the same action as the resolution for scenario 1, to prevent the server from registering the 2nd NIC address in DNS.
Also, because the server is running DNS, you must configure DNS to only listen on the primary IP address. By default, a Windows server running DNS registers all IP addresses that are being used by DNS. To prevent this, open the DNS console right-click on the DNS server name on the left side and go to Properties –> Interfaces tab. From here, select the radio button which says “Only the following addresses”. Then, if necessary, add the primary address to the list below and remove all other IP addresses. Here is an example:
Scenario 3: Windows Server with single network adapter and multiple IP addresses
This is the same as the example at the top of this post. In this case, there is not a clean way to prevent registration of the 2nd IP address in DNS.
If you are in this situation, it would be best to remove the secondary IP address from the adapter and set the IP on another adapter. Then, you can just follow the resolution for scenario 1 or 2.
If you absolutely must configure the server this way and you cannot add another network adapter, then you CAN use the resolution from scenario 1 and prevent the server from registering its addresses in DNS. However, after that, you may have to go into DNS and manually create a DNS entry in the forward lookup zone for the server. Any servers from recent years have at least 2 NICs in them, and lately are even being shipped with 4 onboard NICs. So, having an extra NIC available won’t usually be an issue.
Another way to prevent dynamic registration of DNS records on a server (2000 and 2003, that is) is to modify the registry using the following Microsoft KB article:
According to the article, it can be done globally, affecting all NICs on the server, or on a per-NIC basis. If you decide to try this option, be CAREFUL!