Remote hosts retrying downed DNS server

[Simon Waters]

Marc.Thach at radianz.com wrote:
> 
> I haven't looked at BIND 9 code but I suspect it's similar.

resolver.c and adb.c seem to be the bits.

BIND 9 lobs in a big penalty based on the number of retries only
- ignoring historical data - when it doesn't get an answer.

This assume that the offending recursive resolvers are using
Bind. This is one of the reasons you can query the version
string (dig @server version.bind chaos txt) to see what the
offending machines are using.

Some resolvers don't bother to track time, but just try each
server. Of course similar results would occur if there were
multiple name servers behind a firewall/NAT device/load
balancer, or the NS TTL was too small, and no doubt many other
reasons.