The external interface makes it possible to connect the simulation with real
networks.

In this example the network consists of only one host. Currently the host
can be used to run ICMP and SCTP as echo server or discard server.

To run this example, some parameters have to be adjusted in the omnetpp.ini.

- Make sure that you have libpcap-dev (v1.5.3 or later) installed on your machine. 
- Turn on the "Network Emulation" feature (In IDE / INET Project Properties / Project Features
  (if you forget this you will receive a 'Class "inet::cSocketRTScheduler" not found' error)
- Rebuild INET.
- Set **.ext[0].device to the device name of the interface of the computer
  running the simulation.
- On your server, add a route to the host 10.1.1.1 and set the gateway to the
  IP address of the computer, on which the simulation is running.

Start the simulation with root privileges.