[Pdns-users] Apparent DoS

[PowerDNS User]

Hello,

I am a recent convert from BIND and I am quite happy with PowerDNS. Since I 
installed pdns about a month ago, however, I have suffered 3 serious crashes 
which have brought the server down. A stroll through /var/log/messages 
reveals the following:

----------------------------------------------------
Dec  6 15:09:15 as pdns[12924]: Not authoritative for 'z.mpisi.com', sending 
servfail to 205.234.158.217 (recursion was desired)
Dec  6 15:09:35 as pdns[12927]: Not authoritative for 'z.mpisi.com', sending 
servfail to 205.234.158.217 (recursion was desired)
Dec  6 15:09:55 as pdns[12992]: Not authoritative for 'z.mpisi.com', sending 
servfail to 205.234.158.217 (recursion was desired)
Dec  6 15:10:15 as pdns[3936]: Not authoritative for 'z.mpisi.com', sending 
servfail to 205.234.158.217 (recursion was desired)
Dec  6 15:10:35 as pdns[12924]: Not authoritative for 'z.mpisi.com', sending 
servfail to 205.234.158.217 (recursion was desired)
----------------------------------------------------
The following IP addresses are just a few that have appeared with this 
message: 

66.225.225.225
69.31.111.2
64.202.110.2 
193.27.78.210 
66.254.101.30

I have no idea who z.mpisi.com is and I certainly do not have any entries in 
my database for them, yet my server is being hit every 20 seconds or so until 
there are too many connections and they entire server must be rebooted. 

For a month now, every request has been for z.mpisi.com and comes from a 
variety of IP address. Is there an option somewhere that I can limit the 
connections or ignore bad hostnames or something to prevent this again? Could 
this be a known worm attacking pdns servers?

Thanks for your help.

 - pdnsu