DNS began in the early days of the Internet when the Internet was a small network created by the Department of Defense for research purpose. Before DNS, computer names, or hostnames, were manually entered into a file located on a centrally administered server. Each site that needed to resolve hostnames had to download this file. As the number of computers on the Internet grew, so did the size of this HOSTS file, and the amount of traffic generated by downloading it. The need for a new system that would offer features such as scalability, decentralized administration, and support for various data types became more obvious. The Domain Name Service (DNS), introduced in 1984, became this new system.
With DNS, the hostnames reside in a database that can be distributed among multiple servers, decreasing the load on any one server and providing the ability to administer this naming system on a per-partition basis. DNS support hierarchical names and allows registration of various data types in addition to the hostname to IP address mapping used in HOSTS files. By virtue of the DNS data being distributed, its size is unlimited and performance does not degrade much when adding more servers.
DNS translates between computer hostnames and IP address. DNS works at the Application layer of the OSI reference model and uses TCP and UDP at the transport layer. The DNS model is pretty plain: Clients make requests and get back answers. If a particular server can not answer a query, it can forward it to another, presumably better informed, server.
[...] DNS Servers A DNS server is a computer that runs a DNS server program, such as the DNS Server service or Berkeley Internet Name Domain (BIND). DNS servers contain DNS database information about some portion of the DNS domain tree structure and resolve name resolution queries issued by DNS clients. When queried, DNS servers can provide the requested information, provide a pointer to another server that can help resolve the query, or respond that the information is unavailable or does not exist. [...]
[...] When the setting is enabled, the server caches only those records with a name that corresponds to the domain for which the original queried name was made. Any referrals received from another DNS server along with a query response are simply discarded. For example, if a query is originally made for example.microsoft.com, and a referral answer provides a record for a name outside the microsoft.com domain name tree (such as msn.com), that name is discarded if the Secure Cache Against Pollution option is enabled. [...]
[...] For example, the following command executed at the command prompt returns the IP addresses associated with the fully qualified domain name (FQDN) www.microsoft.com To resolve the query, the Nslookup utility submits the name to the DNS server specified for the primary connection on the local client computer. This DNS server can then answer the query from its cache or through recursion. If you would like to troubleshoot a specific DNS server instead of the one specified for the primary connection on the local client computer, you can specify that DNS server in the Nslookup command. [...]
[...] (Only the DHCP service provided with Windows Server 2003 currently supports this feature.) Once created in the DNS console, an A resource record that maps the host name server1.lucernepublishing.com to the IP address is represented textually within the lucernepublishing.com.dns zone file as follows: Server 1 A Alias (CNAME) Resource Records Alias (CNAME) resource records are also sometimes called canonical names. These records allow you to use more than one name to point to a single host. For example, the well-known server names (ftp, www) are typically registered using CNAME resource records. [...]
[...] When recursion is not disabled (the default), the local DNS server attempts to resolve a fully qualified domain name (FQDN) after a forwarder has failed to do so. This condition is preferable if you want to optimize settings for fault tolerance: if the upstream forwarder is down, name resolution can fall back to the local DNS server . However, when under this default setting the forwarder receives the forwarded query and still fails to resolve it, the subsequent fallback recursion that occurs at the local DNS server is usually redundant and delays an inevitable query failure message response. [...]
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