DNS Redundancy

Martin McCormick martin at dc.cis.okstate.edu
Thu Oct 21 11:32:09 UTC 2010


	The normal procedure on internet-connected systems is to
set the resolv.conf file to include at least 2 domain name
servers. Example:

nameserver	139.78.100.1
nameserver	139.78.200.1

	Last night, I had to take down our primary DNS for
maintenance and lots of FreeBSD and Linux systems began having trouble of various
kinds.

	While I expected the FreeBSD system I was on to hang for
a couple of seconds and then start using the second DNS, it
basically froze while some Linux boxes also began exhibiting
similar behavior.

	I finally manually changed the resolv.conf on the system
I was using to force the slave DNS to be first in the list and
that helped, but loosing the primary DNS was not the slight
slowdown one might expect. It was a full-blown outage.

	Are we missing some other configuration directive for Unix systems
that would make the systems use the redundancy a little
more gracefully than what happened? Otherwise, why have it if
somebody has to manually intervene? The only thing we should
have lost was dynamic updates. The outage lasted for 25 minutes
or so but didn't resolve until the primary came back on line.

	This is my week for asking novice questions, but I don't
get to see what happens when the master goes away all that often
and what I saw wasn't pretty.

Martin McCormick WB5AGZ  Stillwater, OK 
Systems Engineer
OSU Information Technology Department Telecommunications Services Group



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