URL Masking with DNS and/or Mod_Rewrite?

Question

I want to setup a system so that multiple custom domains like [mydomain.com/params] will redirect to [myapp.com/mydomain.com/params]. Can I do this using only DNS s

Answer 1

No, you can't use only DNS for that.

If every domain can run standalone (www.domain.com) this would be a straightforward multi-site setup and does not require mod_rewrite, just a bunch of directives that point to each site.

If you need exactly the setup you describe (http://www.hostname.com/www.2ndhostname.com/directoryname) you would need one with all the domains as aliases, and a mod_rewrite based redirect to point incoming requests to the right directory.