Illustrated TCP/IP by Matthew G. Naugle Wiley Computer Publishing, John Wiley & Sons, Inc. ISBN: 0471196568   Pub Date: 11/01/98

Chapter 230
Name Servers

The programs that keep information about the domain name space are called name servers. The name resolvers do not usually store information, nor are they programmed with information like a name server. All information is kept in the server.

Name servers keep information about some part of the name space, called a zone. Name servers can be “authoritative” about one or more zones. Being authoritative means that this server is all-knowing about the zone. A server can be authoritative for more than one zone, and it can be a primary name server for one zone and a secondary name server for another. However, these functions rarely cross; name servers are either primary or secondary for the zones they load.

There are two types of name servers: primary masters and secondary masters. The primary master builds its database from files that were preconfigured on its hosts, called zone or database files. The name server reads these files and builds a database for the zone it is authoritative for. Secondary masters can provide information to resolvers just like the primary masters, but they get their information from the primary. Any updates to the database are provided by the primary. This system was set up for ease of use. It is also important to note that there should be more than one name server per zone or domain.

Name Servers

Let’s take a simple example. You are host on domain Naugle.com. Specifically, host1.research.Naugle.com. You are looking for a host named labhost.bnr.ca.us. You type in TELNET labhost.bnr.ca.us. The name server on your network is a primary and is not authoritative for the .us domain. Your name server then sends out a query to the root server that it knows about and that root server refers you to the name server for the .us domain. Your name server will send out a request to that name server for .ca. The .ca name server refers you to another name server authoritative for the domain bnr.ca. Your server then sends one final request to that server for information on labhost.bnr.ca. That server responds with the IP address, which your server returns to your workstation. The TELNET protocol then uses that IP address to attempt a connection to your requested destination. A point to bring out here is that the information in the name server database is not dynamic in that it does not know of the status of any station (that station may be turned off, not accepting any new connections, etc). The name server function simply responds to requests for information that is contained in its database.

Name Servers (continued)