I came across this post on
how to create multiple communities in Community Server that have become an entry on the documentation wiki under
Multiple Community Installations, while researching how to do actually that. =)
In the posts there is a third scenario where you can point different
URLs to the same community. Well, you really don't want to do that if
you're thinking of playing well with the search engines. That would
mean you can access to your community through a domain like
www.domain1.com or www.domain2.com interchangeably. Search engines
often penalize sites when finding that they have the same content as
others, and this would be just like that for them.
What you would be better doing is creating a permanent redirect of HTTP
status code 301 from all domains to a primary one. That is to always
redirect www.domain2.com and www.domain3.com, etc. to www.domain1.com
so any link or user going to any of the domains ends in
www.domain1.com. This can easily be achieved with ASP.NET or
configuring IIS directly. Almost all hosting services allow to create
redirects also.