why won't ethernet stay connected for more than a few hours?

Projects Networking, Protocols, and Devices
7

Good deal! Here is the timeout code for that.

    int timeoutCount = 0;

    while(client.connected()) {
      while(client.available()) {
        timeoutCount = 0;
        Serial.write(client.read());
      }

      timeoutCount++;
      if(timeoutCount > 10000) {
        client.stop();
        Serial.println("timeout");
      }
      delay(1);      
    }
    client.stop();

This will prevent the w5100 from locking up if there is a connection break. It will close the connection if no packets received for 10 seconds.

edit: If you plan on using dhcp for the ip, you should call Ethernet.maintain() about once an hour to keep the ip lease active. I highly recommend using a static ip in the shield for long term connections. That way the router can power cycle and not affect the shield ip.