The Domain Name System (Dns)

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DNS
Alexander Zangerl az@bond.edu.au
Bond University

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DNS, Domain Name Service
is an Internet Service http://www.dns.net/dnsrd/docs/whatis.html is a hierarchical, tree structured naming system maps between domain name space and IP address space distributed Internet directory service mapping stored in global database database distributed and delegated across millions of machines most Internet services rely on DNS to work translates Domain Name [from] ip address [to]

translates
ip address [from] Domain Name [to]

service is provided by
DNS Server
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Domain Name
locates an organisation or other entity on the Internet domain names are for human convenience, instead of machine-readable IP-addresses each domain name is made up of a series of character strings (labels) separated by dots: bond.edu.au.

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FQDN, Fully Qualified Domain Name
determines a unique Internet address for any host on the Internet includes hostname and complete domain-name, incl. top-level domain example www.bond.edu.au mri1.tuwien.ac.at

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Top Level Domain (TLDs)
identifies the most general part of the domain name in an Internet address TLD is either a generic top-level domain (gTLD), such as ”com”, or a country code top-level domain (ccTLD), such as ”fr” within every top-level domain there is a list of second-level domains responsibility for operating each TLD is delegated http://www.icann.org/tlds/

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gTLD, generic TLD
best known ones are .org, .com, .net, .edu, .mil, .gov new generic TLDs: .info, . biz, .museum, .... domain names in these TLDs can only be registered through ICANN-accredited registrars

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ccTLD, country-code TLD
TLDs with two letters (such as .de, .mx, and .jp) – established for over 240 countries and external territories – ISO 3166 can provides regional-specific branding that a typical generic TLD does not comment common misconception is that ccTLDs can only be assigned to Web sites physically located in the suffix country – some countries have specific rules for who can register domains using their suffix and for what purposes

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Second Level Domain
second-level domain name includes the top-level domain, e.g. cnn.com. there can be duplication across domains; e.g. howstuffworks.com and howstuffworks.org are completely different domains can be divided into further domain levels must be unique and registered with accredited companies

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DNS Client, Resolver
software within an application that formats requests to be sent to the Domain Name Server for hostname to Internet address conversion user program can be: e-mail, FTP client, http-client, ... resolver must know the name server it should use for converting URLs to IP addresses nearest name server is either at ISP (for individuals) or in company

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DNS Protocol
application protocol used to request resource records from name server normal resource records lookups are done with UDP zone transfers – TCP must be used – transfer entire content of a zone between (usually between primary and secondary DNS server)

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DNS Server
accepts requests from programs or from other name servers to convert domain names into IP addresses, or back every name server has a list of all of the known root servers procedure when request arrives it can do one of four things: answer the request with an IP address by looking in its cache – contact another name server (recursive) – return IP address from another name server to client (iterative) – return an error message because the requested domain name is invalid or does not exist

performs function
Zone Transfer Iterative DNS Query Recursive DNS Query

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DNS Database
large distributed database – handling billions of requests every day through a network of millions of name servers content is organized in zones zones contain everything that is known about a domain...
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