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Two of my AD controllers (both running DNS service) appear to be having a similar issue. Both are throwing lots of events in the DNS events that look like this:

Event Type: Information
Event Source:   DNS
Event Category: None
Event ID:   5504
Date:       5/24/2010
Time:       11:51:38 AM
User:       N/A
Computer:   ALPHA
Description:
The DNS server encountered an invalid domain name in a packet from 76.74.137.6. The packet will be rejected. The event data contains the DNS packet.

That will come with the same event, same time, with a packet from 76.74.137.7 as well. I know this is "Information" not an error, but since it is new and different it bothers me (yes, I fear unexplained change!)

Both machines are running Windows 2003 R2 SP2. The DNS servers are not exposed to the internet.
Both DNS servers are configured to use OpenDNS for Forwarders.
For both servers, this started about a week ago.

Any thoughts on:
1) should I be concerned?
2) how can I stop/fix this?

To keep it interesting, I have a 3rd AD / DNS box. Same domain, different Active Directory site. Same forwarders, yet doesn't have this issue.

[Update]
On a whim, I changed the forwarders on one of the DNS servers to use Google's public DNS (8.8.8.8 and 8.8.4.4) instead of OpenDNS. Didn't change anything, so I think I can eliminate the forwarders as the cause.

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Do any of your machines connect over a VPN to your network? –  Chris S May 24 '10 at 19:38
    
@Chris - Our employees all have the ability to connect over a VPN to our network (using windows native client and a win2k3 RAS server). –  Chris_K May 24 '10 at 20:04

3 Answers 3

Check this link out...go to (4) under 'Troubleshooting common DNS issues'.

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I can confirm that "Secure cache against pollution" check box was already selected. (more here on that topic: support.microsoft.com/default.aspx?scid=kb;en-us;241352) –  Chris_K May 24 '10 at 19:08
    
Is the 3RD AD/DNS box having a different public IP with OpenDNS? or are all the DNS servers on the same public IP with OpenDNS? –  Saif Khan May 24 '10 at 19:11
    
all 3 AD/DNS boxes are on private IPs, but all 3 are using OpenDNS for Forwarders. (does that answer the question)? –  Chris_K May 24 '10 at 19:13
    
Close. Then check the "smart cache" settings and "network shortcuts" over at OpenDNS under the IP address of the subnet for that DNS server. I assuming you have multiple IP settings over at openDNS. –  Saif Khan May 24 '10 at 19:17
    
Gotcha. First two are in an OpenDNS "named" network. Smart cache is off and there are no network shortcuts. 3rd AD is not in a named OpenDNS network so definitely none of the above there. –  Chris_K May 24 '10 at 19:24

I've been seeing the same error message coming from the same IP. My "secure against pollution" box is also checked. Something with that particular IP?

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Once I figure out who is initiating the DNS request (so I know when to expect it) I plan to sniff out the packets and see what's going on. Could just be a DNS record that 2k3 can't handle. Maybe. –  Chris_K May 26 '10 at 21:25
up vote 0 down vote accepted

While still trying to track this down the 5504 errors stopped appearing... I guess it may have been something running on a particular client machine hitting the DNS server in question. Hard to say.

Some additional info can be found in this technet forums thread.

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