Installing and Administering Internet Services

64 Chapter 3
Configuring and Administering the BIND Name Service
Overview of the BIND Name Service
5. The local name server queries a root name server to find the address
of indigo.div.inc.com. A root name server serves the root
domain. It typically stores information about hosts and name servers
one and two levels below the root.
6. If the root name server cannot resolve the host name, it returns the
address of a name server for the inc.com domain.
7. The local name server queries the server for the inc.com domain to
find the address of indigo.div.inc.com.
8. The name server for the inc.com domain may not have information
for the div.inc.com domain. If it does not, it returns the address of
a name server for the div.inc.com domain.
9. The local name server queries the server for the div.inc.com
domain to find the address of indigo.div.inc.com.
10.The server for the div.inc.com domain returns the address of
indigo.div.inc.com to the local name server.
11.The local name server passes host indigo’s address to the resolver,
which passes it to gethostbyname, which returns it to the telnet
process.
The local name server in the nmt.edu domain caches the addresses of
remote name servers, so the next time a local user needs the address of a
host in the inc.com domain, the local name server sends its query
directly to the name server for inc.com instead of querying the root
name server.
Round-Robin Address Rotation
Round-robin address rotation can provide an inexpensive load-balancing
solution.
A virtual host name can map to the addresses of multiple systems.
When the name server supplies address information for a virtual host
name, it rotates the returned order of the addresses. This provides a
mechanism for load-balancing network traffic to each host.
For example, the virtual host name rainbow is created for three systems
named red, blue, and green. The host name rainbow maps to the IP
addresses of red, blue, and green. When applications/services call
gethostbyname()for rainbow, an array of IP addresses is returned
and applications typically use the first IP address in the array. With