A method for setting a link speed of each of a first port and a second port, which are included in a dual port switch, comprising: receiving a link speed setting completion signal from each of the first port and the second port when the link speed of the first port is set through auto negotiation with a first adjacent port of a first adjacent switch and the link speed of the second port is set through auto negotiation with a second adjacent port of a second adjacent switch, respectively, wherein the first adjacent port is connected to the first port and the second adjacent port is connected to the second port, wherein the link speed of the first port is set through data communication between the first port and the first adjacent port connected to the first port, and the link speed of the second port is set through data communication between the second port and the second adjacent port connected to the second port, wherein the link speed of the first port is set to a lower limited link speed among the limited link speed of the first port and a limited link speed of the first adjacent port connected to the first port, and the link speed of the second port is set to a lower limited link speed among the limited link speed of the second port and a limited link speed of the second adjacent port connected to the second port; when the link speed setting completion signals are received, receiving the link speed of the first port and the link speed of the second port; comparing the received link speed of the first port with the received link speed of the second port; blocking a link of the first port when the link speed of the first port is higher than that of the second port; changing the limited link speed of the first port to be equal to the link speed of the second port; and releasing the link of the first port so that the auto negotiation with the first adjacent port is performed again. receiving a link speed setting completion signal from each of the first port and the second port when the link speed of the first port is set through auto negotiation with a first adjacent port of a first adjacent switch and the link speed of the second port is set through auto negotiation with a second adjacent port of a second adjacent switch, respectively, wherein the first adjacent port is connected to the first port and the second adjacent port is connected to the second port, wherein the link speed of the first port is set through data communication between the first port and the first adjacent port connected to the first port, and the link speed of the second port is set through data communication between the second port and the second adjacent port connected to the second port, wherein the link speed of the first port is set to a lower limited link speed among the limited link speed of the first port and a limited link speed of the first adjacent port connected to the first port, and the link speed of the second port is set to a lower limited link speed among the limited link speed of the second port and a limited link speed of the second adjacent port connected to the second port; when the link speed setting completion signals are received, receiving the link speed of the first port and the link speed of the second port; comparing the received link speed of the first port with the received link speed of the second port; blocking a link of the first port when the link speed of the first port is higher than that of the second port; changing the limited link speed of the first port to be equal to the link speed of the second port; and releasing the link of the first port so that the auto negotiation with the first adjacent port is performed again.