Great! This Arduino Ethernet Shield that is based on the Wiznet W5100 Ethernet Chip gives you an easy way to get your Arduino Online. It is directly supported by Arduino official Ethernet Library.

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.

Note: This ethernet shield is not compatible with the Arduino Mega. It is compatible with Arduino Duemilanove (168 or 328). However, if you want to use it with the Arduino Mega, this tutorial shows you how to do so. More discussion about this topic can also be found here.

It has a regular size SD card slot that allows you to make a mini-server. This is our example code to get you started.

The Ethernet shield uses SPI interface. On the Arduino Duemilanove and other ATmega168 / 328-based boards, the SPI bus uses pins 10 (SS), 11 (MOSI), 12 (MISO), and 13 (SCK). On the Arduino Mega, this is 50 (MISO), 51 (MOSI), 52 (SCK), and 53 (SS). Note that even if you're not using the SS pin, it must remain set as an output; otherwise, the SPI interface can be put into slave mode, rendering the library inoperative.

Power on reset issue:

This is an issue with the Ethernet shield that when it is powered on, the reset button has to be pressed to get the Ethernet shield working. This issue is not specific on this Ethernet shield, but exists in all variant of the Arduino Ethernet shields. The issue is caused by the fact that the normal reset time of the Arduino is too short. Unfortunately this issue cannot be solved by software. Below are the solutions to resolve this problem, you may choose one in your preference.

1. Solder a 100 nF (or thereabout) capacitor between the reset pin and GND, the good place to put it is between the reset button of the Ethernet shield. However, by doing this, the Ethernet shield has to be removed from the Arduino while downloading the program to the Arduino, otherwise you will get the following error

avrdude: stk500_getsync(): not in sync: resp=0x00

2. Clip off the reset pin of the Ethernet shield, and connect it with a wire to an unused i/o of the Arduino. So the reset of the Ethernet shield is independent to the Arduino. Before calling the Ethernet library,  enable that output pin, pull it low for 100ms, and then switch the port back to input mode with pullups disabled.