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Old 19th December 2020, 02:52   #12  |  Link
mjb
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Join Date: Dec 2020
Posts: 5
In DNS, a CNAME is an alias, yes, e.g. www.doom9.org could be set up as a CNAME for forum.doom9.org, or you can have just another A record saying that the IP address of www.doom9.org is the same as the one for forum.doom9.org. So that does need to be fixed.

But what I was talking about in the web server (Apache HTTPD, in this case) is a different piece. It is already configured (probably with a ServerAlias directive) to give the exact same responses for www.doom9.org as for forum.doom9.org. When the DNS is fixed, it means everything will once again "work"... but to the crawlers and archivers it is as if there are two separate websites which happen to have identical content.

The proper way to deal with it is to set it up so that the website for the domain you don't want people to linger on (www.doom9.org) responds to all requests with a permanent redirect to the other domain. To do this, an admin has to delete the ServerAlias directive for www.doom9.org and make a separate VirtualHost containing (along with a dummy DocumentRoot and whatever logging directives):
ServerName www.doom.org
RedirectPermanent / http://forum.doom9.org/
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