Disclosed are methods for allocating an address to an Electronic Control Unit (ECU) on an in-vehicle Ethernet network and devices therefor. A method may include allocating a first address value identifying the in-vehicle Ethernet network, allocating a second address value identifying a domain corresponding to the ECU, allocating a third address value identifying a group of ECUs in the allocated domain, allocating a fourth address value identifying the ECU in the group, and generating an IP address including the allocated first to fourth address values. The generated IP address is set as a fixed IP address of the ECU.