If the interface holding IP address 172.16.9.1 is physically connected to the segment where your device (172.16.8.1) resides, then you need to configure a secondary IP address on the interface holding IP address 172.16.9.1.
The command is: ip address 172.16.8.x 255.255.255.0 secondary under the same interface.
Any reason why the router was given an IP address of 172.16.9.x instead of 172.16.8.x?
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Edison.