CRM2015 IFD Internal and External Domains

I am trying to setup CRM2015 with IFD. My internal domain is xr.local and external domain name is somethingelse.com. When going through the directions and searching through the forums I see similar questions regarding with no real information on the possibility. Am I able to set this up to support 2 different domains and where might I find some guidance to do so?

Thanks...

GY