Ulster coach Mark McCall has expressed disappointment that his side have again been drawn in a difficult Heineken Cup group despite being top seeds.
"It seems that being top Irish seeds has not made much difference. It's a very tough, challenging group but the other teams won't fancy playing us.
"Toulouse have a great record in Europe and Llanelli have made some good signings and will be hard to beat.
"London Irish will be tough opponents too as they had a fantastic season."
Leinster are grouped with Edinburgh Gunners, Agen and Gloucester and chief executive Mick Dawson said his province looked forward to "locking horns with our three opponents in what is the premier club competition in world rugby".
"We are under no illusions as to how competitive Pool 2 will be but we are looking forward to what is sure to be an exciting campaign."
Munster face Leicester, Bourgoin and Cardiff Blues and Ireland international hooker Frankie Sheahan conceded that "it will be tough".
"Leicester have been the most consistent team in Europe for the last four or five years and Cardiff finished last season very well, but hopefully we can get through it," he said.