Upvote:2
If your visa has the BIVS endors*m*nt, you can use your visa to enter Ireland but not as the first point of entry.
From the Irish Naturalisation and Immigration Service FAQ:
You should apply for your visa from the country in which you will arrive first. If you plan to travel to Ireland first, and then go the UK, you should apply for an Irish visa. If you apply for a multiple-entry visa, you should note that each time you travel you must arrive first in the country which issued your visa.
AND
If your visa has BIVS marked on it, it can be used to travel to both Ireland and the UK. You must land first in the country which issued your visa.