Methods of detecting a path and forwarding devices are disclosed. In an example of the present disclosure, a first forwarding device constructs a detection packet for a service flow, wherein forwarding information in a packet head of the detection packet is same as forwarding information in a packet head of the service flow; forwards the detection packet based on the forwarding information in the packet head of the detection packet; when an error controlling packet corresponding to the detection packet is received from a second forwarding device in a set time period, the first forwarding device determines an address of the second forwarding device, returns to perform a process of constructing the detection packet for the service flow; otherwise, determines the path of the service flow based on the at least one respective address of the at least one second forwarding device.