Ireland hopeful Johnny Sexton experience has rubbed off on rookies

How Ireland fill the void at flyhalf following Sexton's near unbroken 14-year run in the shirt is by far the biggest question facing their Six Nations defence. The three players competing at the start of the tournament have just 12 caps between them.

With the relatively more tested Ross Byrne out injured, Jack Crowley is the clear favourite to start against France on February 2, with Farrell sure the talented Munsterman learned a lot as Sexton's main understudy at last year's World Cup.

"Hopefully how Johnny has been certainly as a leader but more importantly for those guys as a number 10, a world class once in a generation type player over the last four or five years, if they haven't learned something from that...," Farrell said at the launch of the tournament in Dublin on Monday.

"And not just that, if they're not excited about wanting to take the challenge on and say I'm going to make that my position, then we're going to get to find out a lot about a lot of people's characters in those three players in the coming weeks."

Farrell has no such worries about the character of Sexton's replacement as captain after naming fellow centurion and long-time Munster skipper Peter O'Mahony to lead the side last week.

The 34-year-old flanker described the elevation as "very, very special" and probably the biggest honour of his storied career. To the surprise of Farrell, who was sitting beside him at the event, O'Mahony also said he wasn't expecting the call.

"As far as natural fit, natural leaders coming from before with Johnny, he's the type of leader that is exactly the same," Farrell said of O'Mahony, who has captained his country on 10 previous occasions.

"Certain people, when you walk into a room and they're there, they make the room feel right. It's pretty important around the place and certainly on match day that you have that type of person in the dressing room and Peter's certainly one of those."