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Contrasting stub zones and conditional forwarders

Updated: January 21, 2005

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

Contrasting stub zones and conditional forwarders

There can be some confusion about when to use conditional forwarders instead of stub zones because both DNS features allow a DNS server to respond to a query with a referral for, or by forwarding to, a different DNS server; however, these settings are used for very different purposes. These features have the following objectives:

  • A conditional forwarder setting configures the DNS server to forward a query it receives to a DNS server depending on the DNS name contained in the query.

  • A stub zone keeps the DNS server hosting a parent zone aware of all the DNS servers authoritative for a child zone.

Conditional forwarders

In situations where you want DNS clients in separate networks to resolve each others' names without having to query DNS servers on the Internet, such as in the case of a company merger, you should configure the DNS servers in each network to forward queries for names in the other network. DNS servers in one network will forward names for clients in the other network to a specific DNS server that will build up a large cache of information about the other network. When forwarding in this way, you create a direct point of contact between two networks' DNS servers, reducing the need for recursion.

Stub zones do not provide the same server-to-server benefit because a DNS server hosting a stub zone in one network will reply to queries for names in the other network with a list of all authoritative DNS servers for the zone with that name, instead of the specific DNS servers you have designated to handle this traffic. This configuration complicates any type of security settings that you want to establish between specific DNS servers running in each of the networks. For more information, see Understanding forwarders.

Stub zones

Stub zones are used when you want a DNS server hosting a parent zone to remain aware of the authoritative DNS servers for one of its child zones. If the stub zone for a child zone is hosted on the same DNS server as the parent zone, the DNS server hosting the stub zone will receive a list of all new authoritative DNS servers for the child zone when it requests an update from the stub zone's master server . This method of updating the DNS server hosting the parent zone maintains a current list of the authoritative DNS servers for the child zone as they are added and removed.

A conditional forwarder is not an efficient method of keeping a DNS server hosting a parent zone aware of the authoritative DNS servers for a child zone. If you used this method, whenever the authoritative DNS servers for the child zone changed, the conditional forwarder setting on the DNS server hosting the parent zone would have to be manually configured with the IP address for each new authoritative DNS server for the child zone. For more information, see Understanding stub zones.

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