DNS server cache causing causing network problems
Posted on 2006-11-30
For the past day and a half, something in our DNS cache has been causing our internet access to tank.
Our DNS server is integrated with active directory, and sits on the same network as the rest of our machines. I've discovered that if I disable the DNS service, even temporarily, our internet access comes back. This of course caused problems with just about everything else on our domain because this (for now) is the only DNS server we have locally. I've also noticed that if I go into the DNS console, and clear the DNS cache, then internet access speeds back up to a functional level, but this only lasts a few minutes.
One thing I find suspicious, is that until yesterday afternoon (when I first cleared the cache and reloaded the DNS server), we only had 2 folders in our DNS console. Forward Lookup Zones and Reverse Lookup Zones. We now have a third, Cached Lookups. There's a whole bunch of zone records in there that are for domains in Taiwan, Honk Kong, Argentina, and a few others. This is obviously something wrong or malicious, but when I try to delete the zone record it tells me it can't be deleted because the zone doesn't exist. This may be related, but until an hour ago, we were receiving steady messages in our DNS Event Log saying:
>>The DNS server is configured to forward to a non-recursive DNS server at 18.104.22.168.
DNS servers in forwarders list MUST be configured to process recursive queries. <<
If goes on to give instructions on how to mitigate this, but the address specified (and they're random) is definitely not in my forwarders list. These addresses also resolve to places like Taiwan and Honk Kong.
I've tried to find another way to delete these, but haven't had any luck. Also when I clear the cache, the entries for the garbage zome records start coming back immediate. Does anyone know if this is a sign of a remote DOS attack, or has anyone seen this before in cases where the box may have been compromised?