Briton Froome won the race in 2013 but crashed out of the Tour in the fifth stage last year.
Australian Porte, as well as Ireland's Nicolas Roche, Dutchman Wout Poels and Czech Leopold Konig will assist Froome in the mountains.
Ian Stannard will be Froome's domestique in a treacherous first week featuring cobble and possibly tricky weather conditions.
“He's a powerhouse, his real role will be protecting the team, protecting Chris, he's gonna be absolutely pivotal in the first week,” said team manager Dave Brailsford.
Geraint Thomas, Pete Kennaugh and Luke Rowe have the ability to cover al terrains.
The Tour starts from Utrecht, Netherlands, on Saturday.
Original source: Team Sky bends towards mountains