Due + Ethernet board serial communication

Hi,

I'm working on my first Arduino project, and I need a way to transfer data between Arduino Ethernet and Due boards. I was thinking of using serial, but I read the disclaimer about Due I/O pins only tolerating 3.3 V.

Does that also include serial RX/TX pins? Is it not safe to directly connect the serial pins of Ethernet and Due? If so, what would be the alternatives to make the two boards talk?

Does that also include serial RX/TX pins?

Yes.

Is it not safe to directly connect the serial pins of Ethernet and Due

Yes it is not safe to connect pins of the Ethernet to many chips that are not designed for direct connection. If they are they are called a PHY PHY - Wikipedia

what would be the alternatives to make the two boards talk?

Use a logic level converter between a 5V system and a 3V3 system, this can be as simple as a single transistor or FET.

Okay, I will look into it. Thanks.