something like this: ………………………………………………………………………………….. 192.168.1.2 mail.mycompany.com mail ftp
something like this: ………………………………………………………………………………….. 192.168.1.2 mail.mycompany.com mail ftp www dns dns ………………………………………………………………………………….. Using this /etc/hosts entry, the desktop could find that host (mail.mycompany.com) with either the full domain name or any of the brief aliases listed (such as ftp.mycompany.com, www.mycompany.com, and so on). If you find that you need more than two or three hosts entries, or that maintaining hosts files is becoming a problem, it’s a sign that you need to build a nameserver to handle your hosts data. A nameserver is far more scalable than a hosts file on each machine, and it’s much simpler to maintain once you set it up. The Named Daemon The most popular DNS server software is BIND (Berkeley Internet Name Daemon). (The actual server program is called named(8).) BIND is actually a suite of tools that includes named and supporting programs such as dig. BIND is maintained by the Internet Software Consortium (http://www.isc.org/) and is released under a BSD-style license. While there are competitors, such as djbdns (/usr/ports/net/djbdns), BIND is considered the nameservice reference implementation, so we’ll focus on it. The concepts used in BIND are generally applicable to any nameserver programs. Because BIND has been the target of malicious hackers over the last several years, its most recent version was completely rewritten with a focus on security. It includes some very powerful security features and extremely defensive programming. Masters and Slaves No matter what nameserver daemon you use, you’ll keep running into the terms masters and slaves. Every domain needs at least two nameservers, but only one can be the master; the rest are slaves. A master nameserver is the final authority on a domain. When you make changes to a domain, you make the changes on the master nameserver. The slaves take their information from the master nameserver for that domain. One nameserver can be both a master for some domains and a slave for others. For example, http://absolutebsd.com/ has two nameservers, http://blackhelicopters.org/ and http://ralph.glblnet.com/; http://blackhelicopters.org/ holds the original reference files for this domain, and any changes are to be made on that system. That makes http://blackhelicopters.org/ the master nameserver. Every so often, http://ralph.glblnet.com/ updates its records for this domain from http://blackhelicopters.org/, making it the slave. If the blackhelicopters.org system is abducted by aliens, http://ralph.glblnet.com/ would continue to serve DNS information for http://absolutebsd.com/. On the other hand, http://ralph.glblnet.com/ holds the master records for many other domains, and other nameservers update their records for these domains from http://ralph.glblnet.com/. Therefore, 276
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