While feasibility and obtaining a solution of a given network coding problem are well studied, the decoding procedure and complexity have not garnered much attention. We consider the decoding problem in a network wherein the sources generate multiple messages and the sink nodes demand some or all of the source messages. We consider both linear and non-linear network codes over a finite field and propose to use the sum-product (SP) algorithm over Boolean semiring for decoding at the sink nodes in order to reduce the computational complexity. We use traceback to further lower the computational complexity incurred by SP decoding. We also define and identify a sufficient condition for fast decodability of a network code at a sink that demands all the source messages.