Is this a "DNS only" question or a web hosting question? I assume you are not discussing an e-mail routing question.
You can easily setup vhosts so that multiple domains share the same root folder. That way you get the same pages when you visit domain1.com or domain2.net and there is no redirection.
If all traffic is going to go to domain1.com you can setup an alias (cname) record in your domain2.net DNS server so that all reference to domain2.net go to domain1.com. This is not "redirection" in the sense that clients will still keep pointing to domain2.net.
If you want a user who visits http://domain2.net to magically be served pages from http://domain1.com (as seen in the URL bar) then you are going to use redirects or url rewriting. That is really the best solution in that it forces all traffic to really come/go from domain1.com as expected. You are simply trying to catch people who put in the alternative domain2.net url and send the to the proper place.