I have built an AC701 RGMII Ethernet design in Vivado 2015.1.
The design fails to work correctly with LwIP.
It hangs at the following step:
Also, LwIP is unable to return pings.
This is an issue with the LwIP adapter.
To resolve the issue, please replace the file in the following directory with the file attached to this answer record:
This issue has been fixed in 2015.2.