On RHEL Linux v5, you may expect the following message in your system log :
named[xxxxx]: network unreachable resolving ‘vhost.domain.tld/A/IN’: xxxx:xxx:xx::xxx#53
This is because by default, named try to listen IPv6 even if there is no IPv6 configured on the host. So you need to modify /etc/sysconfig/named and add the following parameter to tell bind to start using IPv4 only :
OPTIONS="-4"