Ok, this is what happens when I don't read the manual.
-d : Force dhclient to run as a foreground process. Normally the DHCP client will run in the foreground until is has configured an interface at which time it will revert to running in the background. This option is useful when running the client undera debugger, or when running it out of inittab on System V systems. This implies -v.
-v : Enable verbose log messages.
-n : Do not configure any interfaces. This is most likely to be useful in combination with the -w flag.
Once I ran
dhclient -d -v -n, discovered what configurations were buggy, and why. Another DHCP was running in the network.
If you want to really get several information, but then some system will need to mess up the DHCP configuration to work, is using WireShark: