The 31-year-old has spent the past seven seasons playing for, and now captaining the Llanelli Scarlets and he worked under Jenkins until last summer.
Jenkins is now in the enemy camp as head coach of Wales, but that precious inside knowledge means Easterby knows exactly what to expect this weekend.
"Gareth Jenkins brings with him a huge amount of passion, whether it is for Llanelli, the Lions or with Wales," said Easterby.
"His appointment was important for their team. They won the Grand Slam and then had a sticky patch last year when Mike Ruddock left.
"Gareth has a lot of positive points and I think we saw that in their autumn campaign. They played some good rugby.
"The big test comes now and he will be as keen as anyone to prove he is the right selection.
"He is an intelligent rugby thinker but most of all he'll get the players on the edge. When they take the field they will know what is expected of them."
Easterby expects Wales to target the Irish front five in the hope of exposing them, just as Leicester did Munster's pack in the European Cup.
"You would expect nothing different from a forward pack coached by Gareth Jenkins," said Easterby.
"They may look at what went on the Heineken Cup when Leicester went to Thomand Park and maybe out-muscled some of the Munster players.
"But that is certainly fresh in the minds of the players who were involved at the weekend. Six of the Ireland pack are from Munster and they want to produce a huge performance to put that right.
"It doesn't get much tougher to go and play first up than Cardiff.
"We have got to physically try and dominate the Welsh and if we can dominate them up front, I think our backs are as good as anyone's in the world."