The ease of access to Tibet from Nepal has made it popular to take the overland route from Kathmandu to Lhasa. The two major overland routes are Friendship Highway at Kodari and Kyirong Highway at Rasuwagadi. The 2015 earthquake in Nepal had disrupted the Kodari entry port, but now it officially repaired and the border is open bring overland journey through this port into operation. You need to get several permits and visas to enter Tibet from Nepal which cannot be acquired individually. Your tour operator needs to apply for the permit you need to travel into and around Tibet.