Why does Local DNS Fail when Internet is down?

[Martin McCormick]

	We are running Bind9 but this question covers behavior
that goes back as far as DNS, itself.  When our connection to the
Internet (root name servers), becomes intermittent, all our
domain name servers start to hang when doing local lookups.  I
have seen Suns exhibit this behavior back as far as I have been
involved with bind which is about ten years.  I have always heard
that it has to do with open file descriptors, but it still
happens today with Bind9 running on a FreeBSD platform.

	As soon as the network comes back to life, so do the
dns's.  In the past, I have killed and restarted them only to
have the hanging return within seconds which tells me it is
something else.

	My questions are:

	What causes this behavior?
Can I configure anything differently at our site to allow the
local world to continue to operate?

	Every time this happens, the rumblings start as to how to
redesign things especially now that we are starting to use Novell
Active Directory and people suddenly can't access their network
drives, etc.

	Our master and slave dns's use the conventional
configuration format of all the local zones and then the root
zone last.

	Obviously, we want to preserve the robustness of dns
in normal operation and not create new single-point failure
modes.  Our present topology works perfectly when the network is
up which is most of the time, but a couple of days of network
hickups and the natives start to get restless.

Martin McCormick Stillwater, OK
OSU Center for Computing and Information services Network Operations Group