Internet Protocol Addressing

Each mchine connected to an IP network (such as the Internet) is addressed using a unique 32 bit number, the IP address.
Many machines will have more than one IP address - for example a machine running virtual websites will have an IP address for each website they host.
Other times a pool of IP addresses is shared between a number of machines - eg on a dynamic-IP dialup connection your machine will be allocated a different IP address each time you connect.
These addresses are usualy written in DOtted Quad notation (IPv4), as a series of four 8bit numbers, wrtten in decimal and separated by periods. For example 151.196.75.10.

Each number is in the range 0 to 255 - so if you ever see something  that looks like an IP address with numbers outside those ranges it's not a real address.


Domain Name System

      On the Internet, the Domain Name System (Dns) associates various sort of information with so-called domain names; most importanly, it serves as the "phone book" for the Internet; it translates human-readable computer hosatnames, into the IP addresses that networking wquipment needs for delivering information. it also stores other  information such as the list of mail exchange servers that accept email for a given domain. In providing a worldwide keyword-based redirection service, the Domain Name System is an essential component of contemporary Internet use. 

Parts of a domain name

 A domain name usualy consists of two or more parts (technically labelss), separates by dots. for example Google.com
  • The rightmost label conveys the top-level domain 
  • Each label to the left specifies a subdivision or subdomain of the domain above it Note that "subdomain" expresses relative dependence, not absolute dependence for example google.com. comprises a subdomain of the Com domain. 
  • A hostname refer to a domain name that has one or more associated IP addresses.
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