We have several developments taking place that require our clients to change their host files in order to view the project in its beta stage or on another server to the one presently being used, so have created this tutorial (and included a video at the end of the article) to help them change their host files.

For reference as to where the HOSTS file is located, please see the following:

The HOSTS file is a text file that contains IP addresses separated by at least one space and then a domain name, with each entry on its own line.

If you wanted to map a domain name within your local environment to a different server to the one mapped by the public DNS you would need to add an entry into your HOSTS file as follows:

When using the Internet most people connect to web sites, ftp servers or other Internet servers by connecting to a domain name. Internet applications do not communicate via domain names, but rather using IP addresses, such as 192.168.1.1. Therefore when you type a domain name in your program that you wish to connect to, your application must first convert it to an IP address that it will use to connect to.

The way these hostnames are resolved to their mapped IP address is called Domain Name Resolution. On almost all operating systems whether they be Apple, Linux, Unix, Netware, or Windows the majority of resolutions from domain names to IP addresses are done through a procedure called DNS.

DNS stands for Domain Name System and is the standard domain name resolution service used on the Internet. Whenever a device connects to another device on the Internet it needs to connect to it via the IP address of the remote device. In order to get that IP address, DNS is used to resolve that domain name to its mapped IP address. This is done by the device querying its configured DNS Servers and asking that server what the IP address is for that particular domain name. The DNS server will then query other servers on the Internet that know the correct information for that domain name, and then return to the device the IP address. The device will then open a connection directly to the IP address and perform the desired operation.

In Windows machines you may not already have a hosts file. If this is the case there will most likely be a sample hosts file called hosts.sam that you can rename to hosts and use as you wish. You can edit this file either from the cmd prompt using Edit or Notepad on windows or VI on Unix/Linux. Really any text editor can open and modify the HOSTS file. It is also recommended that if you use this file that you make periodic backups of it by copying it to another name.

Some people recommend that you make this file read only so that it will be harder to modify by a malicious program, which there are Hijackers that are known to do this, but there are Hijackers such as CoolWebSearch that add entries to the file regardless of whether or not its read only. Therefore you should not think that having your HOSTS as read only will make it safe from modification.

Probably the most common way people block ads like this is with something called the “hosts file”. The hosts file is a simple list of hostnames and their corresponding IP addresses, which your computer looks at every time you try and contact a previously unknown hostname. If it finds an entry for the computer you’re trying to reach, it sets the IP address for that computer to be whatever’s in the hosts file.

127.0.0.1 is a special IP address which, to a computer, always means that computer. Any time a machine sends a network request to 127.0.0.1, it is talking to itself. This is very useful when it comes to blocking ads, because all we have to do is specify the IP address of any ad server to be 127.0.0.1. And to do that, all we have to do is edit the hosts file.

It is important to note that there have been complaints of system slowdowns when using a large hosts file. This is usually fixed by turning off and disabling the DNS Client in your Services control panel under Administrative Tools. The DNS client caches previous DNS requests in memory to supposedly speed this process up, but it also reads the entire HOSTS file into that cache as well which can cause a slowdown. This service is unnecessary and can be disabled.

There are HOSTs file that are already made that you can download which contain a large list of known ads servers, banner sites, sites that give tracking cookies, contain web bugs, or infect you with hijackers. Listed below are web sites that produce these types of hosts files:

hpguru’s HOSTS File can be found here: http://www.hosts-file.net/

The MVPS Host File can be found at: http://www.mvps.org.

Hosts File Project can be found here : http://remember.mine.nu/

If you choose to download these files, please backup your original by renaming it to hosts.orig and saving the downloaded HOSTS file in its place. Using a HOSTS file such as these is highly recommended to protect your computer.

For those that prefer a visual reference, please see the following: