This application discloses a troubleshooting method. In the method, a controller first determines that a fault occurs on a first multi-layer link passing through a first port on a first network device, where the first multi-layer link is a link in a link aggregation group between the first network device and a second network device; the controller then releases an optical layer resource of the first multi-layer link, and deletes the first multi-layer link from the link aggregation group; and the controller further establishes, a second multi-layer link for restoration of the first multi-layer link, based on a first idle port on the first network device and a second idle port on a target network device, and adds the second multi-layer link to a target link aggregation group between the first network device and the target network device. According to this method, a faulty link in an aggregation group can be restored in a multi-layer network.