Beginning Web Development, Silverlight, and ASP.NET AJAX

CHAPTER 10 ■ .NET 3.0: PROGRAMMING WITH CARDSPACE 243
Step 3: Editing the hosts File
The next step in the setup script is to edit your hosts file. Internet Explorer matches the
domain name in the browser address bar to that in your certificate. If they don’t match,
you get the errors in Figures 10-9 and 10-10. When you are setting up a development
environment, you will of course be hosting the applications on localhost, which doesn’t
match the certificates—but Windows provides a methodology to allow you to map IP
addresses to domain names (taking a bypass around the DNS): the hosts file.
This file, found in Windows\System32\drivers\etc, is just called hosts (no extension).
You can open it in Notepad to inspect it. Its structure is very simple: an IP address, followed
by at least one space, followed by the domain name, and an optional comment
denoted by a #.
The default hosts settings will likely look like this:
127.0.0.1 localhost
::1 localhost
The samples installer adds the adatum.com, contoso.com, fabrikam.com, and
woodgrovebank.com sites to hosts, mapping them to 127.0.0.1 (your machine) also.
When the script is done, your hosts file will likely look like this:
127.0.0.1 localhost
::1 localhost
127.0.0.1 www.adatum.com
127.0.0.1 adatum.com
127.0.0.1 www.contoso.com
127.0.0.1 contoso.com
127.0.0.1 www.fabrikam.com
127.0.0.1 fabrikam.com
127.0.0.1 www.woodgrovebank.com
127.0.0.1 woodgrovebank.com
Now, whenever the browser is instructed to go to www.fabrikam.com, it will bypass the
DNS and consider 127.0.0.1 to be the server for this domain. Now the browser will match
the domain name on the URL with that on the certificate, and you’ll be able to access the
site securely.
As the hosts file can be used to bypass the DNS and potentially fool users into
thinking they are on one site when they are on another, it is protected by Windows and
requires administrative access for it to be edited. However, you should check your hosts
file regularly to make sure that it hasn’t been hijacked.
Now that everything is in place, the final step is to install the samples themselves.