The Ethernet Shield allows an Arduino board to connect to the internet. It is based on the Wiznet W5100 ethernet chip (datasheet). The Wiznet W5100 provides a network (IP) stack capable of both TCP and UDP. It supports up to four simultaneous socket connections.
Use the Ethernet library to write sketches which connect to the internet using the shield. The ethernet shield connects to an Arduino board using long wire-wrap headers which extend through the shield. This keeps the pin layout intact and allows another shield to be stacked on top.
Standard Arduino and Arduino Mega compatible
Standard RJ45 Ethernet interface
Arduino Ethernet Library compatible
Support Micro SD Card（no more than 2GB）
Arduino/ Freaduino/Mega fully compatible
Easy to access reset button
Up to 4 TCP/UDP network connections
SD Card IO CS:D4 ;MOSI:D11;SCK:D13;MISO:D12