I have a problem with my DNS setup and I really can't understand what's wrong with it.
We host our own public DNS servers on 2 different networks (technically, we have 3 DNS servers on 3 different IP ranges but only 2 are in different physical locations).
This weekend, the primary DNS server for one of our domains hung (I have no idea why yet, but it's a different matter). Strangely, this caused all external DNS requests for that domain to fail. Now, it's always been my impression than the whole point of providing multiple DNS servers was that if one failed, the others would take over (or rather, that the clients would query next available NS server if the one listed in the SOA failed). Yet, until we restarted the primary server, no query would succeed even though all other DNS servers where up, running and answering properly to queries (Authoritative answer to all requests to the zone).
I've checked that the SOA is correct, that all DNS servers have properly registered glue records and that all responded to NDS queries for domains they are authoritative to.
Any idea ?