URL Tutorial

What is a URL?

I recently gave a little tutorial on URL’s and thought I’d share it here.  Most developers that I know have had this burned into their brains for years but it seems that there are many who have not been so fortunate. 🙂  Let’s start with the basics.

A web page or site is accessed using a web browser using a Uniform Resource Locator (URL).  URL’s are often referred to as an addresses and are pronounced “Earl”.

Let’s use this as our example URL: “HTTP://www.Microsoft.com/default.aspx”

The first section (“HTTP”) is the protocol that the browser or program is to use. What is HTTP?  It is the Hypertext Transfer Protocol or language that is used by your browser to communicate with the web server. Without getting too deep, all browsers and web servers use HTTP to communicate.  What is HTTPS? This is a secured version of HTTP.  FTP is File Transfer Protocol.  These are the three protocols that you will most often use.  You really do not need to understand how any of them work unless you are a developer.  The important thing to know is that when saving important information to a web site (name, address, phone, credit card number, etc…), the site must be using HTTPS.  If an HTTP site asks you to enter important information, do not do it.  I’ll get into the reasons for this later.

The Top Level Domain (TLD) is the “.COM” portion of the URL.  There are generic TLD’s such as ORG, NET, GOV, EDU, and MIL as well as country code TLD’s such as UK, AM, CA, and DE (see http://www.iana.org/domains/root/db/ for a complete list).

Next is the domain name portion of the URL (“microsoft”). What is a domain name?  Basically, it is a human readable “address”.  Under the covers, computers and network equipment numbers (TCP/IP addresses) that are hard for humans to work with and/or remember. The domain names simply maps human friendly text to computer friendly numbers. Domain names are administered by domain name registrars and controlled by the ICANN (Internet Corporation for Assigned Names and Numbers).  They can be “purchased” online and require renewal every few years.  The cost is somewhere in the $20-$30 per year range.  Once you have registered a domain name it is yours for as long as you continue to renew the registration.

The “www” portion of the URL is a sub-domain and is controlled by the person that “owns” the domain name. The owner can create many sub-domains or none. It is entirely their choice.  The “www” is a bit of an “early Internet” carry over that probably will not go away.  Most network administrators map the “www” sub-domain to the same place as the browser would go if it were excluded.  That is to say that “www.JdFinley.com” and “JdFinley.com” will take the user to the exact same place.  In the business world, there are often reasons to map various sub-domains to various business entities to make it easier for the end user find information.

Following the TLD is often a slash and a file name which may include one or more folders.  Our example points to a page named “default.aspx”.  This can be a large number of file types (PHP, HTML, etc…) and is entirely dependent on the programming language and/or tools used to create the website. The folder structure is up to the creator of the web site so you may occasionally see some really strange examples.  A URL such as “HTTP://www.Microsoft.com/files/manuals/manual1.html” simply means that the “manual1.html” file is stored in a  folder titled “manuals” that is contained in a folder titled “files”.

A bit more technical…

HTTPS is Hypertext Transfer Protocol Secured.  This is accomplished by the installation of a Secure Socket Layer (SSL) certificate on the server.  This certificate validates the website as being “who” it says it is.  All communication between the browser and the site are then encrypted so that people/software between the browser and the server cannot see the data being sent back and forth.  Your important data is then protected from prying eyes.

There are a lot of “criminals” on the Internet and they often try to fool people into providing important information.  One of the ways they do this is to create a URL such as “https://paypal.com.abc.de/payment.php”.  Many people will look at this URL, see “paypal.com” and believe the site is legitimate. However; look more closely.  The domain name is “abc” and they have simply added a sub-domain of paypal.com to the abc.com domain.  This is very easy to do and very easy to spot but an amazing number of people get nailed by this scam.

None of this is “secret” or hard to find information but it does not seem to be well known. I hope this helps someone.