The Internet of Things (IoT) facilitates communication among a huge number of uniquely identifiable heterogeneous devices and services without human intervention. To efficiently leverage the benefits of IoT, it is important that IoT applications are secured. IoT also employs large scale deployment of Low power and Lossy Networks (LLNs) comprising of sensors and RFIDs which are resource constrained. These resource constrained devices are connected to the untrustworthy Internet via IPv6 over Low power Wireless Personal Area Networks (6LOWPAN). RPL is the routing protocol used in 6LOWPAN networks which is susceptible to many security attacks. Packet dropping is one of the many RPL security attacks in which a malicious node drops data packets. In this paper, we investigate packet dropping attacks in IoT-LLN and compare their impact the normal scenario. We also present a detection mechanism to identify packet dropping nodes. The mechanism is implemented at the edge of the 6LOWPAN network and hence does not place any computational overhead on the constrained nodes.