SEO impact of using CNAME host both naked and www URL

Question

I have been told I can have two A records on my domain, one with www and one without. However, I have been told can cause SEO issues because google will take it as duplicate content. However when I asked someone about it they said the following:

Google has understood this common configuration for years now. That's ancient SEO advice. If you're really concerned about it, you can always put a canonical meta tag in place to be explicit about it

My question is, assuming I cannot use a redirect (for the sake of this question), is there any SEO impact by having both the naked and the www url on the same CNAME record? Please provide some sort of written example, because there are so many conflicting views.

Solution

It doesn't change SEO whether you use A records or CNAME records at a DNS level. The signals that Google does use for its algorithm are either:

• User facing
• Indicators of web spam

The technical details of your DNS setup are invisible to users and would not indicate to Google that a site is spamming their index.

Duplicate content occurs when the same content is available on two different URLs. To prevent duplicate content on www vs no-www, use 301 redirects to redirect one to the other. To implement redirects, it is the webserver that needs to be configured properly. As long as DNS is pointing to the webserver (either CNAME or A record), then the webserver can be configured properly.

If you cannot use a redirect, then you could use a meta canonical tag on your pages to specific that you specify www or no-www. Or, you could log into webmaster tools and use the configuration option there to tell Google which you prefer.

Comments

[Carl]

Currently I am in the position where I dont think I can easily redirect, since I am using route53. Are you telling me that there is absolutely no penalty for using meta canonical tag or the webmaster tools config. Will google not punish me at all if I use this route, even though there is duplicate content? Thank you for the answer btw!

[Stephen Ostermiller]

I use AWS route 53, it does not prevent you from configuring your webserver to issue redirects. www vs no-www is resolvable with no penalties through several methods now.