Microsoft

Step-By-Step: Standard and conditional forwarding in Windows 2003 DNS

Make your DNS servers more efficient by forwarding unresolved DNS queries. This Step-By-Step walks you through setting up standard forwarding as well as the new Windows 2003 conditional forwarding process.

Forwarding is used to resolve queries that cannot be resolved on the local DNS server. The process involves having a DNS server communicate directly with other DNS servers. When you have your local DNS server directly communicate with outside DNS servers, you reduce the amount of nonlocal site information that is stored in the DNS cache. This allows your local DNS servers to be more efficient with resolving local queries.

Prior to Windows 2003, you could identify multiple servers to which all unresolved queries could be forwarded. If one server was unavailable, the requests would be sent to the next server on the list. This is called standard forwarding in Windows 2003.

Conditional forwarding defines where DNS queries on specific domains are forwarded. This is a new feature available in Windows 2003 DNS. It is designed to work with multiple DNS zone environments in which systems in one namespace (e.g., prep.com) need to communicate with systems in another namespace (e.g., test.com). Also, it can be used for resolution for an intranet (two companies that have merged) or Internet (sharing data with a business partner) scenario.

Setting up standard forwarding

  1. Go to the Start Menu | Administration Tools | DNS to access the DNS service. The DNS Management Tool main appears.
  2. Select the name of your DNS server on the tree hierarchy in the left panel.
  3. Click the right mouse button, and then choose Properties. The DNS properties dialog box appears as shown in Figure A.

Figure A

Notice "All other DNS domains" in the DNS domain field is selected. Any servers added as forwarders while this is selected will be used for standard forwarding (or for any queries involving domains that do not have conditional forwarding defined).

  1. Type the IP address for the server to which queries will be forwarded in the Selected Domain's Forwarder IP_Address List field, and then click Add. The servers used as forwarders will be listed in the order in which they were added (Figure B).

Figure B

You can change the order by selecting an IP address in the list and clicking UP or DOWN appropriately.

  1. Click OK at the bottom of the DNS Properties dialog box once you have finished.


Setting up conditional forwarding
In this scenario, two companies—each with its own network—have merged. They want to keep the network configurations as they are; however, each of the domains used are only resolved internally. Several applications and activities require each of the networks to be able to resolve the domain on the other network. This is a perfect scenario for conditional forwarding.

  1. Access the Forwarders tab in Properties for the DNS server (steps 1 through 3 in the above section).
  2. Click New next to the DNS domain list to add a domain. The New Forwarder dialog box appears as shown in Figure C.

Figure C
  1. Type the domain for which queries will be forwarded in the DNS Domain field, and then click OK. The domain is added to the DNS Domain list on the Forwarders tab (Figure D).

Figure D
  1. Add the IP address for the internal DNS server which maintains the domain locally. As with standard forwarding, you can add more than one forwarder for the domain.
  2. Click OK at the bottom of the DNS Properties dialog box once you have finished.

Additional hints and tips for conditional forwarding

  • Conditional forwarding can only be used for domains for which the DNS server does not hold a primary or secondary zone. This means conditional forwarding can be set for any domain that is at the same level or higher than zones maintained locally. For example, you can set up conditional forwarding to test.com, corp.test.com, or prep.com where example.test.com is a zone maintained locally on the DNS server. However, you cannot conditionally forward for one.example.test.com nor example.test.com.
  • For fault tolerance, it is recommended that you define more than one server as a forwarder for each conditional forward set up. If one server is not available, another one can be queried.
  • Conditional forwarding can replace secondary zones that were used to resolve queries in other namespaces in previous versions of the Windows DNS service.

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