.sdc timing for opencores MAC v9.1

Hello

I‘ m integrating the opencores MAC 9.1 in our Cyclone IV device. For an application I use a simple socket server from the NIOS template. After some Ping commands (~100) I get errors on “Frame dropped”. I’m not an expert in time quest, but I would like to set the a correct timing (.sdc file).

System:
Cyclone IV EP4CE40F23C8
opencores MAC v9.1
MII interface to a DS83848C PHY
NIOS II type fast on 50MHz

Please, can you some one an appropriated .sdc file for the opencores mac v9.1?