How Search Engines View Subdomains

We've been getting questions about the potential search engine optimization (SEO) impact of putting blogs in a subdomain (e.g. blog.mysite.com) vs. a subfolder (e.g. mysite.com/blog). We've also had questions about how search engines (Google) treat subdomains that are on different IP addresses. Unfortunately, Google doesn't have an official statement about these issues, but here are our latest thoughts on the matter.

 

Subdomains link additional pages on your site.

Years ago, spammers figured out that they could set up subdomains and generate inbound links by linking from pages on the subdomains back to pages on the main domain. Google figured this out and plugged that hole in late 2007. Matt Cutts confirms this change in a blog post in December 2007, which also states that it's a “wash” whether you use folders or subdomains. The original post is here: www.mattcutts.com/blog/subdomains-and-subdirectories.

Of course, this is information from 25 years ago in search engine years, but a modern day test confirms that this still holds true. Look at the first page search results for apartments.com—it's all subdomains. It seems reasonable to conclude those results wouldn't be there if Google thought those pages were part of another site.

 

It's okay if your blog subdomain is located on a server with a different IP address.

The next question to tackle is, is it okay for a blog to be hosted separately from the main website. I was able to find absolutely nothing that directly addresses this from Matt Cutts or any other reliable Google authority. But again, a Google search for ardmorecourtapts.com, for example, supports an educated guess. Results include pages from the blog subdomain even though it is hosted at a different location— Yardi hosts the main site while the blog is hosted on a server run by the community's property management company, Trinity Property Consultants.

It makes sense that Google shouldn't care if you have a blog or any functionality running on a separate subdomain. Platform companies—companies that provide Internet solutions for hundreds or thousands of companies through one code base—can't always keep up with end user demand for new functionality, and sometimes it isn’t practical to deploy a solution on a client server (e.g. online rent payment solutions). Even Google makes use of different subdomains for different parts of its business (e.g. maps.google.com, docs.google.com) and they point to separate IP addresses.

So, if you are looking to add a blog or any other technology, and your goal is to maximize SEO for your website, it seems reasonable to conclude that you can host it on a subdomain and on an outside server. However, if you are looking to maximize overall traffic, it's unclear whether you are better off hosting your blog on a separate domain—but that's for another discussion.