Low-Rate DoS (LDoS) attacks degrade the quality of service with less traffic than ordinary DoS attacks. LDoS attacks can easily evade conventional counter-DoS detection mechanisms because their time-averaged flow is small. Thus, LDoS attack is getting a serious problem nowadays. With the recent spread of IoT devices, Zigbee, one of the IoT communication standards, attracts much attention. Zigbee is a low-power wireless communication protocol at the sacrifice of its transfer range and bandwidth. Since Zigbee consumes low power, it is widely adopted for inexpensive small sensors and IoT that run on batteries. The advantage of the low power consumption of Zigbee is due to its use of indirect transmission. However, we newly found that vulnerability to LDoS attacks existed in the indirect transmission. In this study, we first point out this vulnerability and describe new LDoS attack scenarios exploiting it. Next, we propose simple countermeasures against them which require low computational cost. Then, simulation experiments are conducted to evaluate the impact of the attacks and the effectiveness of the proposed countermeasures. The experimental results show that the new LDoS attacks can decrease the normal packet arrival rate to 0% by adjusting the timing of attacks. It is also revealed that our proposed countermeasures successfully prevent such cases and improve the minimum arrival rate to 80% at best.