New domain on multisite, now how to best direct old domain to new site

Hello,

I have an old domain (old.com) that I would like to redirect visitors to a new domain (new.com) which is the main site of a multisite install.

Problem is, that when you go to old.com it redirects to a wp error page that says "Registrations have been disabled" on new.com

This should just display the new.com site, right?

For new.com, I have setup:
a sub-domain wp multisite install (confirmed working)
a dedicated IP(confirmed working)
a wildcard entry in the DNS host (confirmed working)
the mpmudev domain maping plugin (confirmed working)

For old.com, I have:
an A name entry in the DNS host that points to the new.com dedicated IP (confirmed working)

As a troubleshooting measure, I have setup a temporary sub site within the multisite (old.new.com) and this seems to have worked, but this is not my goal. Old.com should just point to new.com.

Here is my question:
What is the best way for me to point Old.com to new.com.

Thanks