This example I want to do My machine -> prg -> fran.
In .ssh/config
:
Host prg
Hostname prgdtu.dk
user fran
Host fran
Hostname 192.168.0.37
ForwardAgent yes
ProxyJump prg
user fran
With ForwardAgent I can pass my ssh key to prg to enter in fran. After this configuration I have to add my key to prg and then to fran.