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Dated: Apr. 06, 2012

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By Vivek Nayyar

Something About Multiple DNS Servers

In medium or large-scale organizations where there are several client computers connected to a network, administrators install multiple DNS servers in order to load balance the traffic and to reduce the burden on a single DNS server. Moreover, if there are multiple DNS servers configured in such network scenarios it is likely that administrators might have configured one DNS server as DNS forwarder and have configured other DNS servers to forward the queries to the forwarder. This is an efficient approach that almost all administrators take for error free and smooth name resolution process.

Keeping these things in mind Microsoft allows administrators to provide IP addresses of multiple DNS servers on every operating system that it releases. The case is not different with Windows Server 2008 R2 as well. Since, Windows server 2008 R2, when installed, works as a client operating system till administrators do not install Active Directory Domain Services (AD DS) on it, just like other client operating systems, it can also be assigned with multiple DNS servers’ IP addresses that may be available in the network. Also, in order to expedite name resolution process from external DNS servers (mostly ISPs’ DNS servers) many times administrators assign external DNS servers’ IP addresses as alternate or additional DNS servers.

In either case, providing multiple DNS servers’ IP addresses on a Windows Server 2008 R2 computer remarkably increases the efficiency of the name resolution process, hence providing fast network flow. However administrators must understand that while providing alternate or additional DNS servers’ IP addresses on a Windows Server 2008 R2 computer automatically makes it a DNS client for the DNS servers, IP addresses of which are assigned to them. In these cases, when a DNS client computer initiates name resolution queries, the queries are recursive in nature.

Utilization of Alternate DNS Servers

When multiple DNS servers’ IP addresses are assigned to a computer, name resolution process occurs according to the sequence in which the IP addresses have been assigned. For example, if a DNS client computer has 192.168.0.1 as its preferred DNS server and 192.168.10.6 as its alternate DNS server, name resolution query only gets forwarded to 192.168.10.6 DNS server if 192.168.0.1 fails to resolve it. If the first DNS server successfully resolves the query, the DNS client computer does not contact alternate DNS server at all.

Assigning Multiple DNS Servers’ IP Addresses

By default the interface where administrators provide DNS IP addresses allows them to assign Preferred and Alternate DNS servers’ addresses. However if administrators want they can assign more than two DNS servers’ IP addresses on Windows Server 2008 R2 computers by following the steps given below:

1.  Log on to Windows Server 2008 R2 computer with administrator account.
2. Assuming that Initial Configuration Tasks window has already been disabled click Start and from the menu click Run.
3. On the opened Run command box type NCPA.CPL command and hit Enter key.
4. On the opened window right click on the NIC on which multiple DNS servers’ IP addresses are to be assigned and from the context menu click Properties.
5. On Local Area Connection Properties box make sure that Networking tab is selected and from the available list double-click Internet Protocol Version 4 (TCP/IPv4).
6. On Internet Protocol Version 4 (TCP/IPv4) Properties box click Advanced button and on Advanced TCP/IP Settings box go to DNS tab.
7. Under DNS server addresses, in order of use section click Add button and in TCP/IP DNS Server box type the IP address of the additional DNS server.

8. Click Add button to add the IP address of the specified DNS server to the list.
9. Use up or down arrows on the left of the box to set the priorities of the DNS servers. The IP address of the DNS server at the top is the first one to which the client computer sends the name resolution queries.
10. Once done, click OK buttons on all the opened windows to allow the changes to take effect.

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