Most people think that all hosting is pretty much the same and so they try to find the lowest price. Low price hosting providers are called bargain hosts. The vast majority of bargain hosts put many web sites on the same IP number because it costs less. IP numbers are not free. They are issued by the American Registry for Internet Numbers (ARIN) and there is a yearly fee. The more IP numbers you have the more the fee is.
The Internet functions through the use of IP numbers. All traffic is routed via these IP numbers. Domain names are meaningless in regards to traffic getting from one point to another. One job of DNS servers is to convert the domain name to an IP number before the traffic is routed to its destination. Core backbone routers disassemble data packets and look for the originating IP numbers and the destination IP numbers and then the packets are reassembled and shipped on.
If a website and other services share an IP number there is a high risk of being blocked. As a customer of a hosting company you have no idea who you are sharing an IP number with. The amount of malicious activity on the Internet is ever-increasing. In fact, we see messages such as the one below everyday and on every server, sometimes from many IP numbers.
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A total of 1 sites probed the server using known hacks
What happens when any systems administrator sees a message such as the one above? They immediately block that IP number from contacting their servers again. However, what happens if a large number of web sites are sharing that IP number? All those web site owners, except one offender, are innocent of any wrongdoing and yet they all get blocked. No traffic of any kind will be accepted from any of them, mail being no exception. It is for this reason that it is called a "secret". None of these web site owners are aware that they have been blocked. The systems administrator responsible for blocking the IP has no simple way of knowing if they just blocked one web site or a thousand of them.
To illustrate this, imagine one thousand cars that all have the same license number. One of them runs a red light and is caught by a traffic camera. All one thousand cars get a ticket. The difference being that at least they would all know about it.
A properly configured server to host business sites has an IP number for each site. When a site owner sends mail it will come from their assigned IP number and not from a shared one, thereby eliminating any impact on the other users of the server if one of them spams.
For a little history, sharing IP numbers on hosting servers was not even possible a few years ago. The change had to do with the way browsers worked. By browsers I'm referring to Firefox, Netscape, Safari, Internet Explorer, etc. Browsers using the version 1.0 standard were not capable of viewing sites that were not on a dedicated IP. When the version 1.1 standard was adopted, which is the current version, it had a feature that allowed the browser to pass the host header to the server. In plain English, this means that the browser could tell the server what site it was looking for once it found the server via the IP number. If you have an old version of Netscape laying around you will find that there are many sites that you are not even able to view. This is because it is using a version prior to 1.1.
Article written by Larry Johnson, Network & Hardware Consultant
© WAASI, Inc.
Last updated: 11th October 2012