i'm searching for a solution for a problem where i need to send some data from 1 arduino with ethernet-shield to multiple others over a lan.
my problem is that the signals should be transmitted as fast as possible , so i thought about multicasting. so i can change the numbers of arduinos without problems and big configuration, cause they all react on the packages.
The standard ethernet library provides only TCP (connection-oriented communication). this is incompatible with multicast.
There has been work done on a UDP implementation for the arduino, but I don't have references off the top of my head. You can in general do multicast with UDP, but I don't know if the UDP code or the wiznet chip can do multicast.
I suspect you really want to do broadcast, not multicast. It's simpler. Same restrictions I just mentioned apply, though.