simple socket server connection established, but cannot ping/telnet

If you can ping the board, there's definitely no problem at the mac/phy levels, so I don't think you need to include that.

Probably you have a wrong SSS code or made a mistake in tcp configuration: infact ping relies on UDP, while the server-client connection requires TCP which is a bit more complex.

Using a network analyzer like Wireshark can easily help you to find out if connection initiates and where it fails before being established.