The Concise Guide to DNS and BINDby Nicolai Langfeldt
The Concise Guide to DNS and BIND provides you with the technical depth and expert-level information you need to understand and administer DNS and BIND. Domain Name System (DNS) is a distributed Internet directory service. It is used mainly to translate between domain names and IP addresses, and to control Internet email delivery. Most Internet services rely on DNS… See more details below
The Concise Guide to DNS and BIND provides you with the technical depth and expert-level information you need to understand and administer DNS and BIND. Domain Name System (DNS) is a distributed Internet directory service. It is used mainly to translate between domain names and IP addresses, and to control Internet email delivery. Most Internet services rely on DNS to work, and if DNS fails, Web sites cannot be located and email delivery stalls. BIND (Berkeley Internet Name Daemon) is an implementation of the Domain Name System (DNS) protocols. This book covers setting up a DNS server and client, DNS domain zones, compiling and configuring BIND, dial-up connections, adding more domains, setting up root servers on private networks, firewall rules, Dynamic DNS (DDNS), subdomains and delegation, caching and name resolution, troubleshooting tools and techniques, debugging and logging, new features in BIND 8.2.2, and it offers introductory information on BIND 9.
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Chapter 1: DNS Concepts
DNS Is a Hierarchic, Distributed DatabaseDNS's hierarchy is the result of two things. The most obvious is the domain names, such as www.amazon.com. This is a hierarchic name that is read from left to right. Rightmost is com, which is one of the many hundreds of topleuel domains, or TLDs. Of these TLDs, com, edu, and org are the most wellknown, but many, many others exist-one for each nation and territory on the planet. The International Standards Organization (ISO) has a standard for two-letter country codes called ISO-3166. The Internet authorities simply adopted these codes as names for these national domains. Under each TLD several more domains exist, such as amazon in our example. In addition, within the amazon domain, you find several more domain names, including the name of a machine (or several machines sharing one name), such as www. Together, the domain names make up www. amazon. com, which is called a fully qualified domain name (FQDN) because no part of the name is left out. Both TLD and FQDN are acronyms often found in technical discussions on the Internet.
However, the hierarchy also comes from one other thing, which is linked with the distribution. Distribution is the way in which the contents of the DNS database are dispensed among servers on the Net. These make a hierarchy, almost in direct relation to the domain name structure. Authorities on the Net, called registrars, have authority over com and the other TLDs.
They give, or delegate, authority over subdomains to the people who manage those subdomains. For instance, people employed by Amazon manage the amazon. com part of the database with their own set of DNSservers that have authority over the amazon. com domain. It is even possible for Amazon, or any other entity, to have several subdomains with delegated authority. This delegation of authority from com to amazon is a very important feature because it distributes both the administrative and technical responsibilities of managing DNS throughout the Net. Herein lies the point of DNS and the reason it can keep growing while the hosts. txt file could not. The delegation of authority over subdomains ensures that DNS is scalable; no single part of DNS will be bogged down by the weight of its responsibilities.
What Is a Domain?DNS is a hierarchic database. A good analog in computing is a tree data structure as used in programming. Similar to a tree data structure, DNS has a root node, edges, and leaf nodes. Because it's a database, it also has lookup keys and values found by these keys by traversing the tree structure.
If you examine a DNS name such as www. amazon. com, you'll see that all these parts are represented in the name. But first, it's important to realize that in reality the DNS name is www.amazon.com. (with the trailing period). The period is not normally typed, but it is there and is significant. It represents the root node of DNS. Just as in programming, you must know where the root node is because it cannot be found automatically. However, after you know where the root of the tree is, everything else can be found. The root is also called the root domain. It and each part of the domain name represent a domain, or subdomain, depending on bow you look at it. To get between the nodes, which are nameservers, edges are necessary, and DNS has edges. In fact, the contents of the DNS database are all edges.
In DNS, each server has a root. hints file that tells it where to look for rootservers (see Figure 1.1)...
Meet the Author
Nicolai Langfeldt is the author of the Linux Documentation Project's (LDP) DNS and NFS HOWTOs, which have been maintained by LDP since 1995. He received his education from the University of Oslo in Informatics (computer science). He has been a UNIX and network programmer, administrator, and consultant since 1993.
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