The IEIK Ethernet Shield for Arduino allows an Arduino board to connect to the internet. It is based on the Wiznet W5100 ethernet chip. 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 that connect to the internet using the shield. 

The new Ethernet shield now includes a micro SD card connector, it is MEGA compatible and an on-board reset controller. 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. 

Arduino uses digital pins 10, 11, 12, and 13 (SPI) to communicate with the W5100 on the ethernet shield. 

These pins cannot be used for General i/o. 

Features 

• Can be used as server or client. 
• Directly plug puzzle board, no soldering required. 
• Based on the Wiznet W5100 Ethernet Chip. 
• This is the latest version of the Ethernet Shield. 
• Directly supported by Arduino official Ethernet Library. 
• Adds a micro-SD card slot, which can be used to store files for serving over the network. 
• Compatible with the Arduino Duemilanove (168 or 328), Uno as well as Mega (1280/2560) and can be accessed . 
• using the SD library. 
• MAC address: 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };.