Installing and Administering Internet Services

Chapter 3 77
Configuring and Administering the BIND Name Service
Overview of the BIND Name Service
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
round-robin address rotation, the name server rotates the order of the
addresses returned, so connections to rainbow will be balanced among
red, blue, and green.
Round-robin address cycling can also affect multi-homed hosts (hosts
with multiple IP addresses). However, if a multi-homed host belongs to
multiple subnets, the address records will be sorted by the resolver to
favor the addresses to which the querying host is directly connected, or
those that correspond to the networks in the querying host’s sortlist
(specified in /etc/named.boot).
Also note that for multi-homed hosts with multipleinterfaces attached to
the same subnet, no load sharing is done for outbound traffic. The