The line is UP, but T101 debug shows that no packets are received
The line is UP, but T101 debugs show that no packets are received, even though RTU is sending packets.
Verify whether the interface is up by entering the show ip interface brief command.
Router# show ip interface brief Interface IP-Address OK? Method Status Protocol FastEthernet0/0 10.64.69.206 YES NVRAM up up Serial0/1/0 unassigned YES NVRAM up up Serial0/1/1 126.96.36.199 YES NVRAM up up
Alternatively, enter the show interface serial 0/1/0 (if the serial number is 0/1/0) command.
Verify whether the RTU is indeed sending packets.
If the router receives partial characters or only some parts of a packet, then the it is possible that the line like parity, stop bits or data bits are configured inconsistently between the RTU and the router. Check the RTU manual and make sure the same parity (even/odd.none), stop bits and data bits are configured on the router too. Use the show line <number> command in the router to view the sync line configurations.
To obtain the line number from the interface identification refer How to find the baud rate, parity, stop bits and data bits used by the interface/line?