Connection timeout message when running nslookup against GNS SCAN Address

Nslookup Error
[root@ns1 named]#  nslookup grac4-scan.grid4.example.com
;; connection timed out; trying next origin
Server:        192.168.5.50
Address:    192.168.5.50#53
** server can't find grac4-scan.grid4.example.com: NXDOMAIN

/var/log/messages of the BIND Nameserver  contains  a lot of IPV6 related errors 
  using GNS host : GNSTESTHOST 
..
Jun 24 15:19:08 ns1 named[7529]: error (network unreachable) resolving 'GNSTESTHOST.grid4.example.com.de.oracle.com/AAAA/IN': 202.12.27.33#53
Jun 24 15:19:08 ns1 named[7529]: error (network unreachable) resolving 'GNSTESTHOST.grid4.example.com.de.oracle.com/A/IN': 2001:503:ba3e::2:30#53
Jun 24 15:19:08 ns1 named[7529]: error (network unreachable) resolving 'GNSTESTHOST.grid4.example.com.de.oracle.com/AAAA/IN': 2001:503:ba3e::2:30#53
Jun 24 15:19:08 ns1 named[7529]: error (network unreachable) resolving 'GNSTESTHOST.grid4.example.com.de.oracle.com/A/IN': 2001:500:2::c#53
Jun 24 15:19:08 ns1 named[7529]: error (network unreachable) resolving 'GNSTESTHOST.grid4.example.com.de.oracle.com/AAAA/IN': 2001:500:2::c#53
Jun 24 15:19:08 ns1 named[7529]: error (network unreachable) resolving 'GNSTESTHOST.grid4.example.com.de.oracle.com/A/IN': 2001:500:2d::d#53
Jun 24 15:19:08 ns1 named[7529]: error (network unreachable) resolving 'GNSTESTHOST.grid4.example.com.de.oracle.com/AAAA/IN': 2001:500:2d::d#53
....
Jun 24 15:19:08 ns1 named[7529]: error (network unreachable) resolving 'GNSTESTHOST.grid4.example.com.de.oracle.com/A/IN': 2001:dc3::35#53
Jun 24 15:19:08 ns1 named[7529]: error (network unreachable) resolving 'GNSTESTHOST.grid4.example.com.de.oracle.com/AAAA/IN': 2001:dc3::35#53
Jun 24 15:19:18 ns1 named[7529]: error (network unreachable) resolving 'GNSTESTHOST.grid4.example.com.de.oracle.com/A/IN': 2001:502:f3ff::64#53

-> All the failed IVPV6 requests add a delay for the request and leads to the nslookup Timeout
-> As our network can't handle IPV6 we need to disable IVP6. 

FIX : Disable ipv6 on CentOS 6/7 / RHEL 6/7 

Edit the /etc/sysctl.conf.
# vi /etc/sysctl.conf
Put the following entry to disable IPv6 for all adapter.
net.ipv6.conf.all.disable_ipv6 = 1

[root@ns1 named]#  ifconfig eth1
eth1      Link encap:Ethernet  HWaddr 08:00:27:2B:5E:DD
          inet addr:192.168.5.50  Bcast:192.168.5.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:2171 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1461 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:159819 (156.0 KiB)  TX bytes:185391 (181.0 KiB)
-> No IPV6 reference anymore 

After disabling IPV6 only very less named records should be logged in /var/log/messages : 
Jun 24 15:49:07 ns1 named[3152]: zone 2.168.192.in-addr.arpa/IN: sending notifies (serial 2009011201)
Jun 24 15:49:07 ns1 named[3152]: zone 5.168.192.in-addr.arpa/IN: sending notifies (serial 2009011201)
Jun 24 15:50:45 ns1 named[3152]: error (FORMERR) resolving 'GNSTESTHOST.grid4.example.com/AAAA/IN': 192.168.5.54#53
Jun 24 16:00:48 ns1 named[3152]: error (FORMERR) resolving 'GNSTESTHOST.grid4.example.com/AAAA/IN': 192.168.5.54#53
Jun 24 16:10:50 ns1 named[3152]: error (FORMERR) resolving 'GNSTESTHOST.grid4.example.com/AAAA/IN': 192.168.5.54#53
Jun 24 16:16:52 ns1 named[3152]: client 192.168.5.101#29873: RFC 1918 response from Internet for 5.1.168.192.in-addr.arpa
...

Nslookup should now  work fine 
[root@ns1 log]#  nslookup grac4-scan.grid4.example.com
Server:        192.168.5.50
Address:    192.168.5.50#53

Non-authoritative answer:
Name:    grac4-scan.grid4.example.com
Address: 192.168.5.200
Name:    grac4-scan.grid4.example.com
Address: 192.168.5.165
Name:    grac4-scan.grid4.example.com
Address: 192.168.5.166

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