Gikfun Ethernet Shield W5100 for Arduino UNO R3 Mega 2560 1280 EK7011 The 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. Ethernet Shield W5100 for Arduino UNO, Mega 2560,1280 AVR MAC address: 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };