[CentOS] [OT] DNS queries issue

[Ray Van Dolson]

> I show millions of lines like:
> Oct  4 11:49:30 dns1 named[878]: client 68.13.16.20#53535: query (cache)
> denied
> 
> If I trim out those and the last message repeated lines, I go from a
> messages log of 1.8GB to 1.3MB but 2 weeks earlier my messages log for
> the week was only 339M.
> 
> Googling for the query (cache) denied didn't seem find anything useful,
> that this is other name servers attempting to query my servers for info.
> 
> Its this something I need to bear with in having a publically available
> DNS server with authoritative domains? Is there a way to suppress these
> messages from going to syslog and is it a bad idea to do so?
> 
> There have been no configuration changes except to add 1 or 2 domains to
> the nameservers.

Interesting... it might be worthwhile to determine what all these
clients are asknig for.  You mention adding a few new domains to the
nameservers.. are you the SOA for them?  Should Internet clients _be
allowed_ to query your DNS server for these records?  Perhaps
allow-query is misconfigured on your server?

Even if you aren't expecting any internet-sourced traffic to your DNS
server it would be interesting to examine what exactly they are asking
for.  You could do this with a packet sniffer or query logging in BIND.

Also perhaps you could do an analysis on all the IP's in the denied
messages and see if there are any IP's or subnets that pop up... might
indicate some sort of DDoS activity that you could track down and
report.

Last resort would be to just block inbound DNS traffic from the
Internet if you're not needing to answer queries originating from
there.

1.8GB's of these seems incredibly excessive... I wonder if they're not
legitimate DNS requests trying to get to you because you're the SOA for
some domain... 

Ray