PoE Ethernet Mezzanine doesn't establish connection to LAN

I’m using the PoE mezzzanine with the Ultra96v2 board and the PYNQ system image. The lan78xx driver is included in PYNQ. The mezzanine appears as interface eth0. When I connect the board to the PoE switch, the board powers up. The switch reports that it’s delivering 10 Watts and the link is established at 1000Mbps. But the ultra96v2 doesn’t get an IP address from DHCP. Assigning the IP address manually with ifconfig doesn’t work. The eth0 interface has the assigned IP address, but it can’t ping anything on the network.