Recently, internet of things has drawn attention among the academicians, governments and engineers from various sectors. There are many critical issues in IoT such as security, scalability, big data analytics. Availability, interoperability, performance, mobility. This paper focus on providing optimal routing among the various networking environment such as wired wireless and sensors in the IoT. In this paper the major research issues involved in the existing routing protocols to meet the requirements of internet of things are reviewed the major issues involved in the design of a routing protocol and the different classification of routing protocols are studied. The major challenges of the internet of things, must address the problem of dynamic topology, scalability, mobility of nodes and limited bandwidth. The review covers different kinds of routing protocols such as reactive, proactive, hybrid, location aware, hybrid, multicast, multipath, Geocast, power aware and hierarchical existing geometric routing protocols have been sensibly studied which involves discussion on routing techniques, the advantages and disadvantages of the existing work area analysed in order to help the future researchers. The analysis of existing routing protocols is carried out based on shortest path, least transmission time. Finally, a research open challenge in routing which needs to be addressed by the research and academic community are discussed. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.