Please explain someone to me, what is difference in terminology between ALIAS domain and MASK redirect and CNAME settings? What are they used for, with some examples please. And what are their influence on SEO? I am just confused, are they all the same thing or not?
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should be on serverfault imho.
if i understand your question right, you are mixing different concepts.
a CNAME is DNS "alias" for an Hostname. eg.
This has no influence to SEO, as most Servers can serve more than one homepage under the same IP. (Named Based Virtual Host)
Alias (ServerAlias) is used in Apache Vhost - Config to let a Vhost appear under different hostnames.
Not sure what you mean about "Mask redirect".
The ServerAlias leads to duplicated content. as for searchengines your content is under different domain names. In Googles Webmastertool you can configure this. But SEO People say its better to redirect all addional hostnames via 301 to the main domain.