rel=nofollow a subdomain

I have a subdomain that i use for advertisements. It has openx installed to serve the ads. How can I ensure that everything from the subdomain gets treated like adding rel=n开发者_Go百科ofollow as I don't want Google and other search engines to think that we think the ads are worth following.

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your are looking for the X-Robots-Tag HTTP header

in the .htaccess of the server of your subdomain

Header set X-Robots-Tag "nofollow"

see google http://code.google.com/web/controlcrawlindex/docs/robots_meta_tag.html

seems to be supported by bing, too http://www.bing.com/community/site_blogs/b/webmaster/archive/2009/08/21/prevent-a-bot-from-getting-lost-in-space-sem-101.aspx