6LoWPAN standardized by IEEE 802.15.4 permits nodes in a wireless sensor network (WSN) to communicate using Internet Protocol (IP). An adaptation layer introduced above the MAC layer achieves header compression, fragmentation and reassembly of IP packets. Routing protocols in 6LoWPAN differ depending on the application and the network architecture. This paper presents a comprehensive survey on the recent developments in 6LoWPAN routing protocols. The advantages and the performance issues of the routing protocols are highlighted in this paper. A comparative study about various routing protocols existing in 6LoWPAN is done using key routing performance metrics.