Solution

Execute the display ip routing-table command on Device A and Device C to view whether Device A has a route over tunnel 0 to 10.2.0.0/16 and whether Device C has a route over tunnel 0 to 10.1.0.0/16.

If such a route does not exist, execute the ip route-static command in system view to add the route. Take Device A as an example:

[DeviceA] ip route-static 10.2.0.0 255.255.0.0 tunnel 0