Posted by: paragon | December 27, 2007

What is DNS : Network-Internet Propagation

What Is DNS?

  • DNS is a distributed database that is the default naming system for IP-based networks. DNS names are user-friendly, which means that they are easier to remember than IP addresses.
  • DNS names remain more constant than IP addresses.
  • DNS is used to resolve computer names to an IP address and to locate computers within local networks as well as on the Internet.
  • Host names refer to specific computers on the Internet or a private network. A host name is the leftmost portion of a fully qualified domain name (FQDN), which describe the exact position of a host within the domain hierarchy (Example: spiceworks.rocks.com).

How DNS Works In Theory

Domain names, arranged in a tree, cut into zones, each served by a nameserver. The domain name space consists of a ‘tree” of domain names. Each node or leaf in the tree has one or more resource records, which hold information associated with the domain name. The tree sub-divides into zones. A zone consists of a collection of connected nodes authoritatively served by an authoritative DNS nameserver. (Note that a single nameserver can host several zones.) When a system administrator wants to let another administrator control a part of the domain name space within his or her zone of authority, he or she can delegate control to the other administrator. This splits a part of the old zone off into a new zone, which comes under the authority of the second administrator’s nameservers. The old zone ceases to be authoritative for what goes under the authority of the new zone. A resolver looks up the information associated with nodes. A resolver knows how to communicate with name servers by sending DNS requests, and heeding DNS responses. Resolving usually entails iterating through several name servers to find the needed information. Some resolvers function simplistically and can only communicate with a single name server. These simple resolvers rely on a recursing name server to perform the work of finding information for them.

Types Of DNS Records

  • An A record or address record maps a hostname to a 32-bit IPv4 address.
  • An AAAA record or IPv6 address record maps a hostname to a 128-bit IPv6 address. (Spiceworks does not work with Ipv6 at this time)
  • A CNAME record or canonical name record is an alias of one name to another. The A record to which the alias points can be either local or remote – on a foreign name server. This is useful when running multiple services (like an FTP and a webserver) from a single IP address. Each service can then have its own entry in DNS (like http://ftp.example.com. and http://www.example.com.)
  • An MX record or mail exchange record maps a domain name to a list of mail exchange servers for that domain.
  • A PTR record or pointer record maps an IPv4 address to the canonical name for that host. Setting up a PTR record for a hostname in the in-addr.arpa. domain that corresponds to an IP address implements reverse DNS lookup for that address. For example (at the time of writing), http://www.icann.net has the IP address 192.0.34.164, but a PTR record maps 164.34.0.192.in-addr.arpa to its canonical name, referrals.icann.org.
  • An NS record or name server record maps a domain name to a list of DNS servers authoritative for that domain. Delegations depend on NS records.
  • An SOA record or start of authority record specifies the DNS server providing authoritative information about an Internet domain, the email of the domain administrator, the domain serial number, and several timers relating to refreshing the zone.
  • An SRV record is a generalized service location record.
  • A TXT Record allows an administrator to insert arbitrary text into a DNS record. For example, this record is used to implement the Sender Policy Framework and DomainKeys specifications.
  • NAPTR records (“Naming Authority Pointer”) are a newer type of DNS record that support regular expression based rewriting.

Other types of records simply provide information (for example, a LOC record gives the physical location of a host), or experimental data (for example, a WKS record gives a list of servers offering some well known service such as HTTP or POP3 for a domain). When sent over the internet, all records use the common format specified in RFC 1035 shown below.

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