if not devices or len(devices) != 1:
msg = "planetlab::ns3::TunTapFdLink must be connected to exactly one PlanetlabTap"
self.error(msg)
if not devices or len(devices) != 1:
msg = "planetlab::ns3::TunTapFdLink must be connected to exactly one PlanetlabTap"
self.error(msg)