Hi, CAN Bus shield and Arduino Ethernet shield both use SPI for communication with Arduino board. Thus, they cannot be used at the same time.
CAN Bus shield takes D9/D10(selectable) as SS pin.
Arduino Ethernet shield takes D10 for W5100 and D4 for SD slot as SS pins if you are using it with Arduino UNO.
So CAN Bus shield and Arduino Ethernet shield are not conflicting on hardware. Some modifications in the libraries are required to combine them together. Thanks!
