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

In this example the network consists of eight clients, four switches,
three routers, and an extRouter, which connects the simulation
to a real host.

This network can be used to apply traceroute, a tool to trace the
path through the network to a specified host.

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

- 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 nets 10.2. and 10.3., and set
  the gateway to the IP address of the computer on which the simulation is
  running.

Start the simulation with root privileges. To get realistic round trip times
you should choose the express mode.

Type traceroute 10.2.1.1 at the command prompt of the external machine.






