How can I play the CnC mod 'Rise of the Reds' multiplayer?
Ever since the official support through GameSpy disappeared when GameSpy shut down in July 2014, multiplayer for the post-RA2 C&C games is provided by the community servers of the CnC-Online project. Check out their Setup page for more info on how to get it running.
Playing mods on their system should not be a problem, according to their FAQ.