A method for establishing an Ethernet communication link of a digital protective relay having at least two communication ports, the method comprising: configuring physical layers of a first communication port and a second communication port, wherein the first communication port is coupled to a first Ethernet controller and the second communication port is coupled to a second Ethernet controller; determining whether or not auto-negotiation with respect to the first communication port or the second communication port is successful; and replacing configuration information regarding one of physical layers of the first communication port and the second communication port with configuration information regarding the other of the physical layers of the first communication port and the second communication port, according to whether or not the auto-negotiation with respect to each one of the first communication port and the second communication port has been successful, and establishing, by the communication port which has failed the auto-negotiation, a communication link by using configuration information regarding the communication port which has successfully performed physical layer configuration and auto-negotiation as configuration information regarding the communication port which has failed the auto-negotiation, thereby establishing an Ethernet link for each communication port, wherein the determining of whether or not the auto-negotiation with respect to each of the first communication port and the second communication port has been successful comprises: initiating a timer having a set expiration term and determining whether or not the timer has expired (S204, S207). configuring physical layers of a first communication port and a second communication port, wherein the first communication port is coupled to a first Ethernet controller and the second communication port is coupled to a second Ethernet controller; determining whether or not auto-negotiation with respect to the first communication port or the second communication port is successful; and replacing configuration information regarding one of physical layers of the first communication port and the second communication port with configuration information regarding the other of the physical layers of the first communication port and the second communication port, according to whether or not the auto-negotiation with respect to each one of the first communication port and the second communication port has been successful, and establishing, by the communication port which has failed the auto-negotiation, a communication link by using configuration information regarding the communication port which has successfully performed physical layer configuration and auto-negotiation as configuration information regarding the communication port which has failed the auto-negotiation, thereby establishing an Ethernet link for each communication port, wherein the determining of whether or not the auto-negotiation with respect to each of the first communication port and the second communication port has been successful comprises: initiating a timer having a set expiration term and determining whether or not the timer has expired (S204, S207).