hi.
which is the best Ethernet shield i can use for my mega 2560 r3 board , i have an old Arduino Ethernet shield could i use that ?.
i have tried it and i seems that it does not work but it ok on a Arduino Duemilanove.
I don't know anything about your current Arduino shield but I understand the Due is a 3.3v device and therefore, if that shield works OK on it, it is a non-standard device and cannot be expected to work on a Mega. In the meantime the plain vanilla W5100 shield available for $7.50 on eBay works just fine on a Mega, it being made for that purpose.
The older ethernet shields did not have the ICSP connector. If the ethernet shield does not have the ICSP connector on the bottom of the shield, it will not work without some pin jumper wires.