Huge DNS traffic recieved and showing NXDomain*-, bind becomes unresponsive.

Issue

• We have DNS service running on RHEL6 for domain resolution and we found multiple time named service going hung status.
• We are noticing lots of NXDOMAIN responses for valid domains from dns server.

13:05:17.336324 IP x.x.x.x.53 > 10.x.x.x.41336: 31018 NXDomain*-| 0/0/1 (53)
13:05:17.337570 IP x.x.x.x.53 > 10.x.x.x.23769: 62592 NXDomain*- 0/0/1 (240)
13:05:17.346635 IP x.x.x.x.53 > 10.x.x.x.29450: 26900 NXDomain* 0/1/1 (105)
13:05:17.347492 IP x.x.x.x.53 > 10.x.x.x.53891: 21013 NXDomain 0/1/1 (162)
13:05:17.358850 IP x.x.x.x.53 > 10.x.x.x.40031: 30860 NXDomain*-| 0/0/1 (55)

• nslookup was getting timed out

DNS request timed out.
    timeout was 2 seconds.
DNS request timed out.
    timeout was 2 seconds.
Non-authoritative answer:
DNS request timed out.