The success of blockchain as the underlying technology for cryptocurrencies has opened up possibilities for its use
in other application domains as well. The main advantages of blockchain for its potential use in other areas are its
inherent security mechanisms and immunity to data manipulation attacks. A blockchain relies on a consensus method
for agreeing on any new data. Most of the consensus methods which are currently used for the blockchain of different
cryptocurrencies require high computational power and thus are not suitable for resource-constrained systems. <div><br></div><div>In this article, we survey the various blockchain-based consensus methods that are applicable to resource-constrained
IoT devices and networks. In a typical IoT network, there exist several devices with limited computational and communication capabilities. Most often, these devices cannot perform intensive computations and are starved for bandwidth.
Therefore, we discuss the possible measures that can be taken to reduce the computational power and convergence time
for the underlying consensus methods. We also talk about some of the alternatives to the public blockchain, such as
private blockchain and tangle, along with their potential adoption for IoT networks. Furthermore, we review the existing
consensus methods that have been implemented and explore the possibility of utilizing them to realize a blockchainbased IoT network. Some of the open research challenges including AI-enabled blockchains are also put forward. </div>