Munster will host Toulon in the quarter-finals of the Champions Cup, while Saracens will travel to Dublin to take on Leinster following the conclusion of the pool stages.
Ulster's hopes of progression to the quarter-finals of the Champions Cup fell apart at a wet, cold and muddy Ricoh Arena as Wasps powered to a bonus-point Pool 1 victory.
Johann van Graan's side upped the gears in the second half at Thomond Park to ease to a 48-3 victory over Castres to seal their 17th appearance in the knockout stages.
A win turned out to be all Munster required for a home quarter-final, and before they claimed the bonus point, would have faced La Rochelle. The try-fest however ensured they will now face the Top 14 side in Limerick.
Saracens, courtesy of a 62-14 victory against Northampton in their final Pool Two fixture on Saturday, scraped through as third best runners-up, and their reward is to take on in-form Leinster who won all six of their pool games.
Munster and Leinster are on opposite sides of the draw and can not meet until the final should they both progress.
Should Leinster get the better of a Saracens side seeking a third consecutive Champions Cup win, they would have home advantage against Scarlets, but would have to travel to if La Rochelle advance at the expense of the Welsh region.
Munster would be on the road regardless of whether they face Clermont Auvergne or Racing 92 in any potential semi-final pairing.
The quarter-finals are set for March 30th, 31st and April 1st.