Classy Munster book home quarter-final
Castres took the lead through Rory Kockott and dominated the first 15 minutes, before a pair of Ian Keatley penalties put the home side in front.
Man of the Match Keith Earls then scored Munster's first try of the afternoon on 32 minutes, to give the Irish province a 10-point lead at the interval.
Rhys Marshall added a second try four minutes after half-time, before Munster took over with a further penalty try just before the hour mark.
Simon Zebo ensured a bonus point victory with a superb try, darting past two Castres defenders before diving over the whitewash.
Alex Wootton and James Cronin added a fifth and sixth try in the closing stages to put further gloss on a comprehensive victory for Munster.
The Irish province will host RC Toulon in the Champions Cup quarter-finals at Thomond Park.
Tries: Earls, Marshall, Penalty try, Zebo, Wootton, Cronin
Cons: Keatley 3, Hanrahan 2
Pens: Keatley 2
Yellow Cards: Thomas Combezou (Castres), Daniel Kotze (Castres)
Munster: 15 Simon Zebo, 14 Andrew Conway, 13 Chris Farrell, 12 Rory Scannell, 11 Keith Earls, 10 Ian Keatley, 9 Conor Murray, 8 CJ Stander, 7 Chris Cloete, 6 Peter O’Mahony (captain), 5 Billy Holland, 4 Jean Kleyn, 3 Stephen Archer, 2 Rhys Marshall, 1 Dave Kilcoyne
Replacements: 16 Niall Scannell, 17 James Cronin, 18 John Ryan, 19 Darren O’Shea, 20 Jack O’Donoghue, 21 Duncan Williams, 22 JJ Hanrahan, 23 Alex Wootton
Castres: 15 Geoffrey Palis, 14 Kylian Jaminet, 13 Thomas Combezou, 12 Robert Ebersohn, 11 David Smith, 10 Julien Dumora, 9 Rory Kockott, 8 Alex Tulou, 7 Steve Mafi, 6 Yannick Caballero, 5 Thibault Lassalle, 4 Alexandre Bias, 3 Damien Tussac, 2 Jody Jenneker, 1 Antoine Tichit
Replacements: 16 Kevin Firmin, 17 Tudor Stroe, 18 Daniel Kotze, 19 Victor Moreaux, 20 Baptiste Delaporte, 21 Yohan Domenech, 22 Yohan Le Bourhis, 23 Afusipa Taumoepeau
Referee: Ben Whitehouse (Wales)
Assistant referees: Wayne Davies (Wales), Dewi Phillips (Wales)
TMO: Jonathan Mason (Wales)