The basic addresses on the internet are IP-addresses consisting of four octets separated by three dots: [0-255].[0-255].[0-255].[0-255]

As human beings are very bad in remembering numbers, people have introduced a way to translate IP-addresses into a string of characters.

For instance “www.stringcat.com” is an alias for IP-number “72.41.67.231”, and IP-number “72.41.102.87” denotes the domain “www.secure.stringcat.com”.

An additional advantage of using names is that the underlying IP-numbers are allowed to be changed without invoking the necessity of changing the names as well.

Uri’s

The location of files in the internet is denoted through url's (universal resource locators) and uri's (universal resource identifiers). The idea is that url's uniquely identify the location of a file somewhere in the world. In addition the locators give information on how to get at that information (for instance ftp, http, etc.). So a full uri could be “http://www.stringcat.com”.

http://en.wikipedia.org/wiki/Uniform_Resource_Identifier

Name servers

The translation from names to IP-addresses is done through ‘name servers’, which are computers (or programs) dedicated to this task. There is a worldwide network of connected name servers that use extensive caching to minimize the necessary for look-ups. But finally a lookup request should end in a translation to an IP-number that the SMTP server of your provider, or your browser can use.

Spoofing

Double-lookup (translating the name into an IP-address and then vice-versa) is one of the techniques for spotting malicious users. Spoofing IP-addresses can be detected in this way. In addition, if your browser sends out an http request, both an IP-address and a server set name lookup can be used to detect credulous users.

http://en.wikipedia.org/wiki/Uniform_Resource_Locato

Core protocols

On the internet there are two core transport protocols: UDP and TCP.

Using UDP, programs on networked computers can send short messages known as datagrams to one another.

UDP can also stand for “Unreliable”. This does not mean you will lose all your data, but it does not provide the reliability and ordering guarantees that TCP does. Datagrams may arrive out of order or go missing without notice. UDP does not have the overhead of checking if every packet actually arrived.

The TCP protocol guarantees reliable and in-order delivery of sender to receiver data.