I have implemented an Ethernet UDP communication on the Virtex-5 LX50 card (it uses the DP83865 Ethernet controller) and everything is fine. This application is based on the "Ethernet IP" project implemented by Igor Mohor.
Now I want to enable the same UDP ethernet communication on the Virtex-4 LX25 card, whose controller is the DP83847. But the following report appears in WireShark (see attached chart)

Could someone help me and tell me what I have to modify regarding the configuration in Virtex-5?

Yeah, you've got a bit of a problem there, huh? I'm further going to guess that your problem comes down to the difference between the RGMII/GMII and the MII interface.

You might find the ethernet controller I put together useful. While it's not packaged as a separate core, you should find all the files you need there to use it.

I can't promise that it will work for you though, since part of what will make it work depends upon how you wish to interface with it. The core itself was built for being controlled by the ZipCPU over a wishbone B4/pipelined interface.

Dan