Monday, January 26, 2009

DNS forwarders registry key

A local DNS Server's Forwarders registry key holds a list of boundary dns server's IP addresses which are responsible for forwarding dns queries from local dns servers to remote dns servers. Here the local dns server acts as a dns client on behalf on it's dns clients..

The registry key is located at "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\DNS"

Key Name: Forwarders
Default: NoKey (No forwarders)
Value: list of forwarders ip addresses.

Using DNS Forwarders is useful in following ways:
1. Save network traffic on slow links:

Suppose local DNS server uses low speed broadband/dial up connection to an ISP boundary server. And If local DNS server sends queries to remote servers, it may use up all the network bandwidth for sending recursive queries to remote servers. But if ISP's DNS server acts as a forwarder, then ISP server will do recursive queries to remote servers and returns the single final result to the local dns server.

2. Reduced remote traffic.

The forwarder dns server's dns cache, particularly in a environment where multiple local dns servers exists, is very much useful. When ever a local dns server sends a query, the forwarder looks in to its cache. If found, returns response immediately which saves remote traffic and round trip time.

Note: If the Forwarders key does not exist, then the local DNS server uses the normal iterative query process to answer recursive queries for remote names.


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