The RS-E4GC board is 4-port GBIC LAN board. The GE interfaces do not configure the auto negotiation by default. This does not apper in the configuration files.
The interface state's information is:
Negotiation disabled, full-duplex, 1000Mbps
The interface configuration is empty
The S5648P switch has been connected. The interface state for NE40 is UP, the interface state for S5648P is DOWN.
Need add the configuration command - "negotiation auto" on the router's interface.
The interface of S5648P is configured with "negotiation auto" by default. The NE40 router's interface is NOT configured with "negotiation auto" by default. As a result, the S5648P's interface cannot determine the link's speed/duplex and keeps the DOWN state.