A connection between the subnets behind the gateways moon and sun is set up.
Using the forecast plugin additionally all 224.0.0.251 mDNS multicasts are going
to be tunneled.
The authentication is based on X.509 certificates. Upon the successful
establishment of the IPsec tunnel, mDNS multicasts sent by alice are
received by bob and vice versa whereas unfortunately multicasts originating
from the gateways moon and sun themselves are not tunneled.