Use of multiple sub-domains for load balancing & micro sites -

Multiple domains load balancing (www1.nameofsite.com, www2.nameofsite.com)

Use of multiple sub-domains in this fashion is often done for load balancing purposes. Multiple domains can lead to duplicate content which in turn can lead to a penalty. this is now required less and less due to server capabilities and bandwidth. As a result, Use 301 redirects towards the primary domain on any duplicate domains.

View - domain and server redirections / types of redirects

Sub-domains for micro sites (campaign.nameofsite.com)

Sub-domains are often used to segment differing content (rather than using a directory structure) which then creates a new and unique site in the eyes of the engines. Therefore, any links between sub-domains will hold greater perceived weighting because they will be seen as external rather than internal links within the site (Assuming that each sub-domain has some history & link popularity).

Google has recently cracked down on this vulnerability saying that algorithms will soon only allow a maximum of two subdomains to be indexed in results at the same time. This will potentially hurt sites like wikipedia and ebay which get pages of listings on their brand term due to subdomains.

This was to combat how some sites used subdomains to gain multiple search result listings in the engines (and directories) to have more "search shelf space". For these reasons sub-domains were a useful SEO strategy provided the content contained in each sub-domain is unique enough to stand on its own. Otherwise there was a risk of duplicated content penalty. However, we have always suggested that subdomain use be kept to a minimum.

The use of sub-domains should only be used on large established sites and to a limited basis. New sites (and/or smaller sites) should keep all visibility in a central location (under the main domain), as it will struggle to build initial link strength for more than just the brand term. In addition to that, sub-domains must contain unique content.

Sub-domains are recommended though, if the micro site's offer plans on being short term (and being pulled back from the site within a few months). That way, it can gain its initial visibility slightly faster instead of other pages within the same site showing up for the query entered.

From past experience, we will usually recommend www.nameofsite.com/subsection - over subsection.nameofsite.com about 95% of the time. The usual exception is a short term advertising type campaign.

Usage of subdomains is more of a case by case basis, as you see. If you do want more information on this, please contact us

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