What Are Subdomains? (subdō-mān) (n.) Also called a child domain, is a domain that is part of a larger domain name in DNS hierarchy. DNS hierarchy consists of the root-level domain at the top, underneath which are the top-level domains, followed by second-level domains and finally subdomains. For example, in the domain name client.ewebguru.com, "client" is a subdomain of the larger second-level domain "ewebguru.com." Why Use A Subdomain? Some people create subdomains for niches. Others use them to load images that coincide with their main site; there are some businesses that use them to split their departments. Many uses can be found and the benefits are that you dont have to start another website, thus incurring another expense. Another benefit is that search engines will count the subdomain as a separate site causing more exposure. A subdomain configuration is very similar to a domain name configuration. The only difference is that the subdomain entry is tied to the corresponding domain name lookup. A request for the subdomain (e.g. http://client.ewebguru.com) will be routed to a DNS server containing the DNS information for the parent domain (ewebguru.com). Once the DNS record for the subdomain is resolved to a particular IP address, the request is sent to the web server listening on that IP address. The web server can now delegate the request to the particular website based on the subdomain name in the host header of the request object. Various combinations of subdomain configurations are possible by using DNS server entries and web server application setup for load distribution, application isolation or security purposes. Subdomain Setup on DNS server The forward lookup zone of the parent domain in the DNS server should contain a pointer to the sub domain using either an alias (CNAME), a hostname (A) or a mail exchanger (MX) entry. The alias (CNAME) record is used for a subdomain if the subdomain points to a website running on the same web server at the same IP address as the parent domain website. A new hostname (A) record is used if the subdomain points to a different web server or to the same web server listening on a different IP address (as in the case of load distribution). Alias (CNAME) Setup: An alias points the subdomain to the same web server, which hosts the website for the parent domain. The canonical names (CNAMES) are added for each of the subdomains as shown below. Once the subdomain is resolved to the IP address of the web server, the web server can route the request to a different. Note that an alias for www is setup as a subdomain by default by most hosting companies, so that a request to www.domain.com is sent to the same website that handles the requests for domain.com.
What is subdomain
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