One of the major challenges in 6LoWPAN is to provide continuous services while mobile nodes' movements with minimizing network inaccessible time caused due to handoffs. Even though MIPv6, HMIPv6, and PMIPv6 are commonly accepted standards to address this in IP networks, they cannot inherently avoid the degradation in communication quality during handoff, since they are not designed with consideration of constrained node networks like 6LoWPAN. In this paper, we propose a new fast mobility management protocol for 6LoWPAN, named intra-MARIO. To minimize handoff delay and enhance service availability, intra-MARIO introduces three important components, which are a fast rejoin scheme for handoff management with an adaptive polling based movement detection and multi-hop pointer forwarding schemes for location management. To justify the effectiveness, we have conducted extensive simulations by comparing intra-MARIO with prior schemes like a basic mobility management scheme and a PMIPv6-based protocol. We then implement intra-MARIO on top of our 6LoWPAN platform (SNAIL) and evaluate the performance of intra-MARIO. The results highlight that intra-MARIO reduces overall handoff delay with low power consumption and minimizes packet losses during handoffs, compared to prior mobility protocols.