The networking is as follows:
The figure shows a typical square network. The entire network runs dynamic routing protocol Open Shortest Path First (OSPF). The NE40E functions as an area border router (ABR). The cost is set to 50 on the interconnection interface of the NE40E. When the network runs properly, the test PC connects to the test server using the route identified by the yellow line. When USG5530-01 is faulty, the test PC connects to the test server using the route identified by the red line.
When USG5530-01 goes Down, the test PC fails to connect to the test server.