Using GNS simulator with only one router without any connections, I have noted that with the "no shutdown" command
an ethernet interface remains in a down/down state, as I expected.
If I configure an IP address instead, the "no shutdown" command take the interface in a up/up state, as I did not expected.
As there is not the cable, I expected that there was a problem with the keepalive message.
Is there a problem with the simulator? How do the router work in real world?