[jedberg]

A relevant sidenote: If you're going to do this, make sure you don't allow the content to also be accessible on the top level domain with a different URL, and that one redirects to the other. Two reasons for this:

- Security: You want the cookies to be limited to the subdomain

- SEO: You get penalized if the same content is available at two URLs, because it is assumed it's a copy

The SEO issue applies in the other direction too. When we first set this up for reddit (you could and still can go to subreddit.reddit.com), we found out that we were getting penalized for having the same content on both URLs. So we set it up to redirect the subdomain to the /r/subreddit URL since that was the canonical URL and the cookies didn't matter.

[xyheme]

Thanks, I now learn double content s have this effect on SEO :)