Configuring the web server for subdomains
Once the DNS server is setup to send the request for the subdomain to the corresponding IP address, the work of the web server begins. The web server needs to be configured appropriately to handle the request for the subdomain based on either the IP address or the host header entry. Host headers are commonly used by web servers to host multiple domains or subdomains on one IP address.

Microsoft Windows IIS : In case of Internet Information Server (IIS), create a new web site for the subdomain using the IIS Manager, and add the subdomain (e.g. subdomain.domain.com) as a new host header value listening to the same IP address as specified in the DNS entry. The port is set to 80 (the default for http requests). The host header can be added by clicking on the advanced tab next to the IP address configuration for that web site application. If the subdomain points to a subdirectory of the web site for the domain, then set the home directory for the subdomain web site to the subdirectory. For example, if the domain.com points to C:Inetpubwwwroot and the subdomain needs to be setup for C:Inetpubwwwrootsubdomain, then the directory for the subdomain website should be set to C:Inetpubwwwrootsubdomain.