We have a bind9 DNS server installed on our network running on an Ubuntu system. Normally it works just fine, but every 20 minutes or so, it will stop working for about 3 minutes. Normally if I "dig mylocalhostname" it will return a local ip from our local bind server. However, during those 3 minutes, the answer comes from an external DNS server. Any ideas why this might be? Its incredibly annoying. What kind of steps can I take to narrow down the problem?