301 Redirect where 2 domains point to same IP?

Question

I have 2 TLDs example.com and example.ie.

example.com and example.ie both point at the same IP address and pull the same content now we could get whacked with a ban hammer from Google for duplicate content so we want anyone accessing *.example.ie and *.example.com to be redirected to www.example.com the problem is as they are both pointing at the same server the .htaccess is the same thus I don't believe we can do the usual:

Options +FollowSymlinks
RewriteEngine on
rewritecond %{http_host} ^example.com [nc]
rewriterule ^(.*)$ http://www.example.com/$1 [r=301,nc]

So how do we go about creating a search-engine friendly 301 redirect from *.example.ie and *.example.com to www.example.com?

Answer 1

I would do it like this:

RewriteCond %{HTTP_HOST} !^www\.example\.com$ [NC]
RewriteRule ^(.*)$ http://www.example.com$1 [R=301,L]

That will redirect (statuscode 301 "permantly moved") every domain which is not www.example.com to www.example.com.

Answer 2

The 301 redirect you posted is just fine; the HTTP header of every request (nowadays) contains the name of the host.

As an alternative, you can use rel=canonical. It's not that urgent anyway, as duplicate content on just two domains is unlikely to be a problem.