def local_port_range(self):
        """Tuple of (low_port, high_port) reflecting the local port range
        assigned to outbound connections. We use this as part of a heuristic
        to determine whether a connection is inbound or outbound.
        """
        if self._local_port_range is None:
            with open('/proc/sys/net/ipv4/ip_local_port_range', 'r') as f:
                self._local_port_range = tuple(map(int, f.read().split('\t')))
        return self._local_port_range