RPL is the default routing protocol for IPv6-based Low-Power Wireless Personal Area Networks (6LoWPAN). In an RPL-based 6LoWPAN, wireless sensor nodes or IoT devices connect to the network via DODAG Information Solicitation (DIS) packets with a predetermined time interval. A compromised or malicious node can use the abovementioned technique to broadcast unauthorised DIS messages to neighboring nodes to conduct routing attacks, such as DIS flooding attacks. In this paper, we conduct a simulation-based analysis of the impact of the DIS flooding attack on RPL-based 6LoWPAN under four distinct scenarios, each with two test cases. Scenario 1 is the reference topology, devoid of attacker nodes or test cases. From scenario 2 to scenario 4, the number of DIS attacker nodes increases from one to three to five. In each scenario, in test case A, all attacker nodes are deployed outside the sink node's radio range; in test case B, all attacker nodes are deployed within the sink node's radio range. Our study shows that increasing the number of attacker nodes and deployment location significantly negatively impacts PDR, E2ED, and power consumption. In the case of five DIS attackers nodes deployed within the sink node's radio range, the experimental result decreased PDR by 4.5%, E2ED increased by 62.98%, and the average power consumption increased by 126.7%.