Take care to increment the serial number when editing a zone file.
If the serial number is not incremented, the master nameserver has the correct, new information, but the slave nameservers are never notified of the change and do not attempt to refresh their data of that zone.
Be careful to use ellipses and semi-colons correctly in the /etc/named.conf file.
An omitted semi-colon or unclosed ellipse section can cause named to refuse to start.
Remember to place periods (.) in zone files after all FQDNs and omit them on hostnames.
A period at the end of a domain name denotes a fully qualified domain name. If the period is omitted, then named appends the name of the zone or the $ORIGIN value to complete it.
If a firewall is blocking connections from the named program to other nameservers, edit its configuration file.
By default, BIND version 9 uses random ports above 1024 to query other nameservers. Some firewalls, however, expect all nameservers to communicate using only port 53. To force named to use port 53, add the following
line to the options statement of /etc/named.conf:
query-source address * port 53;