The Irish provinces have been handed challenging assignments for next season's Champions Cup but avoided the 'group of death' containing last season's finalists Saracens and Clermont.
Munster, the only Irish side among the top tier of seeds, were drawn with Racing 92 and Leicester for the second consecutive year, along with a second French team, Castres.
Rassie Erasmus' side beat Racing home and away in last season's competition, hammered Leicester 38-0 at home and lost to the two-time winners away.
Be seeing @DonnachaRyan back in Thomond park soon enough! #pool4 #ChampionsCupDraw
— Robin Copeland (@robocopey) June 8, 2017
Leinster and Ulster were both in the second tier of seeds.
The Northerners will have a tough task against the table-toppers of both the Premiership, Wasps, and Top 14, La Rochelle. Their group also contains Harlequins, who were sixth last season in England.
Leinster will take on English champions Exeter, Montpellier and familiar Pro12 foes Glasgow.
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Montpellier were also in Leinster's pool last season, the Irish side winning at home and losing away.
Saracens became the fourth team to defend their European title after toppling Clermont 28-17 at Murrayfield last month, and the fierce rivals will meet again after being paired together in Pool 2.
Completing a heavyweight group are Guinness PRO12 semi-finalists the Ospreys and play-off winners Northampton.
Pro12 winners Scarlets have been paired with three-time champions Toulon, Bath, and Benetton Treviso in Pool 5.
In the Challenge Cup, Connacht have been drawn in Pool 5 alongside Worcester, who finished 11th in the Aviva Premiership and Top 14 sides Brive (eighth) and Oyonnax.
Oyonnax were promoted this year as Pro D2 champions.
The first round of games will take place on the weekend of 13-15 October, with the finals of both competitions taking place in Bilbao on 11-12 May.
Champions Cup draw
Pool 1: Wasps, La Rochelle, Ulster, Harlequins
Pool 2: Clermont, Saracens, Ospreys, Northampton
Pool 3: Exeter, Leinster, Montpellier, Glasgow
Pool 4: Munster, Racing 92, Leicester, Castres
Pool 5: Scarlets, Toulon, Bath, Benetton
Challenge Cup draw
Pool 1: Newcastle, Dragons, Bordeaux, Enisei-STM
Pool 2: Blues, Sale, Lyon, Toulouse
Pool 3: Gloucester, Pau, Zebre, Agen
Pool 4: Stade Francais Paris, Edinburgh, London Irish, Krasny Yar
Pool 5: Brive, Connacht, Worcester, Oyonnax
