To configure a model to run in External mode over Ethernet:
Open a model that is configured for External mode. For example, open
Communicating with Arduino Mega 2560 Hardware by typing
Open the Configuration Parameters dialog box.
In the External mode>Communication
interface parameter, select
Make sure that you have configured the Ethernet Shield properties as described in Configure Network Settings for Arduino Ethernet Shield.
Your model is configured to run in External mode over the TCP/IP network.
For normal mode and the External mode, the IP address you have specified is used, by default.