I am working on contiki as my academic work, now i have question which file i should refer specificaly from example folder in contiki for simulating schenario like - 30 node iot having ipv6 node , all these node send data to master / gateway node whenever any request come from outside that is from native linux host machine. So communication series is like any host outside IoT request some data from any of 30 IoT nodes via Gateway node/Border Router.
For the border-router look in examples\ipv6\rpl-border-router and for your nodes in examples\ipv6\rpl-udp. Then run the tools\tunslip6 on your linux machine connected to the border-router through usb.
Have a look here.