Apple Mac OS X Server (Administrator’s Guide) - Manual (Page 523)

DNS Service 523
Check Your Configuration
To verify the steps were successful, launch the Terminal application located in /Applications/
Utilities and enter the following commands (substituting the local domain name for
“example.com” if different):
nslookup server.example.com
nslookup 10.0.1.2
Note: If this generic configuration example does not meet your needs, Apple recommends
that you do not attempt to configure DNS on your own and seek out a professional
consultant or additional documentation.
Load Distribution With Round Robin
BIND allows for simple load distribution using an address shuffling method called round
robin. You set up a pool of IP addresses for several hosts mirroring the same content, and
BIND cycles the order of these addresses as it responds to queries. Round robin has no
capability to monitor current server load or processing power. It simply cycles the order of an
address list for a given host name.
You enable round robin by adding multiple address entries in your zone data file for a given
host. For example, suppose you want to distribute Web server traffic between three servers
on your network that all mirror the same content. Suppose the servers have the IP addresses
192.168.12.12, 192.168.12.13, and 192.168.12.14. You would add these lines to the zone data
file db.example.com:
www.example.com 60 IN A 192.168.12.12
www.example.com 60 IN A 192.168.12.13
www.example.com 60 IN A 192.168.12.14
When BIND encounters multiple entries for one host, its default behavior is to answer
queries by sending out this list in a cycled order. The first request gets the addresses in the
order A, B, C. The next request gets the order B, C, A, then C, A, B, and so on. Notice that the
TTL is set quite short to mitigate the effects of local caching.
Setting Up a Private TCP/IP Network
If you have a local area network that has a connection to the Internet, you must set up your
server and client computers with IP addresses and other information that’s unique to the
Internet. You obtain IP addresses from your Internet service provider (ISP).