HP-UX IP Address and Client Management Administrator's Guide HP-UX 11i v2, HP-UX 11i v3
The request-ixfr clause determines whether the local server, acting as a slave, requests
incremental zone transfers from the given remote server (a master server). If set to yes,
incremental transfer is requested from the given remote server (master server). If set to no, all
transfers to the remote server are non-incremental. If this clause is not set, the value of the
request-ixfr option in the global options block is used as the default.
How BIND Works
This section describes how the name server resolves host names. Consider the structure of the
DNS name space illustrated in Figure 1-1. When a user logged in to host venus in the nmt.edu
domain types the following command,
telnet indigo.div.inc.com
the following events occur:
1. The telnet process calls the gethostbyname routine to obtain the Internet address of
indigo.div.inc.com.
2. The gethostbyname routine invokes the BIND resolver, which consists of a set of routines
for querying name servers.
3. The resolver constructs a query and sends it to a name server. If the local host is not running
a name server, the local host must contain a file called /etc/resolv.conf, which contains
one or more Internet addresses for name servers that serve the local domain. If the local host
does not have an /etc/resolv.conf file, the resolver sends the query to the local name
server.
4. The name server daemon, named, receives the query from the resolver. Because the name
server has information about only the hosts in its local domain (nmt.edu), it cannot answer
the query with the information in its local database.
5. The local name server queries a root name server to find the address of
indigo.div.inc.com. The 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 contain information for the div.inc.com
domain. If so, 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 the remote name servers,
so that 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 provides an inexpensive load-balancing solution.You can map a
virtual host name 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
BIND Name Service Overview 19