Ireland opened the scoring when Farr landed an early penalty and they improved on that when Rantz-McDonald took a pass from hooker Conor Muldoon to score the opening try.
Eight points to the good at the break Ireland went further ahead when Farr landed penalties in the 50th and 55th minutes with the decisive try coming from Black before the visitors scotred a late consolation try.
Ireland: Alan McCormack (Navan); Stephen Mulhall (Colaiste Iosagan), Dale Black (Portadown), Rory Sloan (Exiles), Max Rantz-McDonald (Clontarf); Joseph Moran (Naas), Neville Farr (Banbridge); Callum Black (Exiles), Conor Muldoon (Monivea), David Ryan capt (Highfield); Ben Nagle (Sundays Well), Edmund Orr (Armagh); Darren Twomey (Sundays Well), Matthew Irvine (Banbridge). Kieran Moloney (New Ross). Replacements: Kevin Griffin (Kilfeacle & District) for C Black 68 mins; David Weir (Banbridge) for Muldoon 50 mins; Liam Casserly (Galwegians) for Twomey 58 mins;
Referee - G Copsey (Eng).