DNS server stops responding to lookups

Issue

• A DNS server configured on Red Hat Enterprise Linux 5 stops responding to DNS queries.
• A restart required to restore services.

• The DNS process stops servicing requests with the following messages in the logs

  Aug 11 05:55:02 dns1 out of memory [4918]
  Aug 11 06:00:03 dns1 out of memory [4918]
  Aug 11 06:05:06 dns1 out of memory [4918]
  Aug 11 06:08:18 dns1 out of memory [4918]
  Aug 11 06:11:03 dns1 out of memory [4918]