You are right:
U-Boot> ping 192.168.2.2
macb0: PHY present at 0
macb0: link up, 100Mbps full-duplex (lpa: 0xcde1)
Using macb0 device
ping failed; host 192.168.2.2 is not alive
U-Boot>
Problem is that in tftp server I only have access to 127.0.0.0.1 (loopback). 192.168.2.2 is dimmed and I cannot select it.