You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: A Survey of Limitations and Enhancements of the IPv6 Routing Protocol for Low-power and Lossy Networks: A Focus on Core Operations 
Chapter Title:  2) Memory Limitations in the Storing Mode 
1. Abstract of Cited Paper (BIB001):  RPL, the IPv6 Routing Protocol for Low-Power and Lossy Networks, supports both upward and downward traffic. The latter is fundamental for actuation, for queries, and for any bidirectional protocol such as TCP, yet its support is compromised by memory limitation in the nodes. In RPL storing mode, nodes store routing entries for each destination in their sub-graph, limiting the size of the network, and often leading to unreachable nodes and protocol failures. We propose here D-RPL, a mechanism that overcomes the scalability limitation by mending storing mode forwarding with multicast-based dissemination. Our modification has minimal impact on code size and memory usage. D-RPL is activated only when memory limits are reached, and affects only the portion of the traffic and the segments of the network that have exceeded memory limits. We evaluate our solution using Cooja emulation over different synthetic topologies, showing a six-fold improvement in scalability.

Literature Review:
RPL requires that every node running the storing mode of operation must maintain the routing state of all nodes in its sub-DODAG (a node's sub-DODAG represents the set of other nodes whose routing paths to the root are passing via that node)  BIB001 . Although RPL is designed specifically for small and constrained-memory sensor nodes, the protocol has the ambition to handle dense networks comprising up to thousands of nodes. In such high-density networks, it is highly likely that the routing state need to be maintained will overflow the storage capacity of such constrained devices BIB002 . Hence, an overflowed node will be unable to accommodate all routing entries required to be maintained in its routing table, rendering several destinations in its sub-DODAG unreachable from the root point of view enforcing the root to drop the packets destined to such unreachable destinations BIB001 [116].