Description

The Arduino-compatible Ethernet Shield allows an Arduino board to connect to the internet. It is based on the Wiznet W5100ethernet 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 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.

The Ethernet Shield has a standard RJ-45 connection, with an integrated line transformer and Power over Ethernet enabled.
There is an onboard micro-SD card slot, which can be used to store files for serving over the network. It is compatible with the Arduino, Crowduino and Mega (using the Ethernet library). The onboard microSD card reader is accessible through the SD Library. When working with this library, SS is on Pin 4.

There is also the w5200 Ethernet Shield for you.

Specification

Operating voltage 5V (supplied from the Arduino-compatible Board)
Ethernet Controller: W5100 with internal 16K buffer
Connection speed: 10/100Mb
Connection with Arduino-compatible on SPI port
The Shield contains several informational LEDs
PWR: indicates that the board and shield are powered
LINK: indicates the presence of a network link and flashes when the shield transmits or receives data
FULLD: indicates that the network connection is full duplex
100M: indicates the presence of a 100 Mb/s network connection (as opposed to 10 Mb/s)
RX: flashes when the shield receives data
TX: flashes when the shield sends data
TX: flashes when the shield sends data
COLL: flashes when network collisions are detected