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David Neudorfer
Asked: 2012-07-17 15:50:41 +0800 CST

Windows DNS Server slow response time

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Our Windows 2008 R2 SP1 DNS server has a response time of > 3500ms but as low as 1.2ms with a mean of 124ms. I am using OpenDNS for my forwarders. I also enabled 'scavenge stale resource records' and installed the IPv6 disabled hotfix and I'm wondering is slow just because it's Windows? scavenge stale resource records

Fastest vs Mean Response time

domain-name-system windows-server-2008-r2

2 Answers

  1. The plus 3 second time may indicate a network or configuration issue. A few things that may be timing out:

    • Dropped packet. The second packet is often sent after a 3 second delay. Tunable on some stacks.
    • Failing primary DNS. DNS stacks will timeout and try the next server after a delay, generally moving to the second server. Cached values will be returned immediately (xx ms).
    • UDP access to DNS blocked, or failing due to packet size.

    Try using nslookup with the server specified to test DNS access.

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  2. Packet drops would be my first guess.

    But you should be sure that you let incoming ICMP answers back to your DNS server. If your path to OpenDNS has some MTU issues (using tunnels or vpn ?) or if for some reason one DNS server is down, you should receive a proper ICMP message back.

    Also don't forget that the DNS protocol also use TCP port 53 (DNSSEC should use it for instance).

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