En effet mais dans cette doc il ecrit que NM que NM devrait fire le routage vers la connection internet cable d'ou mon probleme:
NetworkManager now should connect to itself (which means it creates the ad-hoc wireless network and routes any internet traffic to your wired network interface). Now connect with the client(s) and you should have a working internet connection.
[^] # Re: ip_forward
Posté par Albert_ . En réponse au message probleme reseau ad-hoc. Évalué à 2.
NetworkManager now should connect to itself (which means it creates the ad-hoc wireless network and routes any internet traffic to your wired network interface). Now connect with the client(s) and you should have a working internet connection.
https://help.ubuntu.com/community/Internet/ConnectionSharing