A PHY chip for a synchronous Ethernet system includes N network input/output (I/O) ports, a first external recovered clock input, a first recovered clock output, and a first clock multiplexer having a plurality of data inputs, a select input, and an output coupled to the first recovered clock output, at least one of the data inputs coupled to a first recovered clock from a respective one of the N network I/O ports, a first additional data input coupled to the first external recovered clock input.