One FE port of NE40 is set to Hardware is WAN-FastEthernet; that is, the port could be configured with IP address directly. However, the port is not configured with ip address command.
According to the configurations of NE40, the port has been set to the observing port in port mirroring: observing-port Ethernet1/0/6, so the port cannot be configured with IP address directly. The problem is solved by deleting the configuration for observing port.
The configuration is problematic.