Reading Modbus TCP/IP thru Cisco 2960 getting Timeout Errors

[ryero]

Hi all,

I'm having some odd issues when trying to read Modbus TCP registries from a Modbus device to a Schneider PLC via a Cisco 2960X. From what I've read, there no need to set much configuration on the Cisco 2960X. Since the PLC will act as the Modbus TCP Server.

Modbus TCP device <---> Cisco 2960x <---> Schneider PLC

The read command occasionally times out and gives back a read timeout error. So we are getting data once in a while. Once thing we have noticed is that the Modbus device is only 10BaseT, though the 2960x is noted to be compatible with 10/100/1000.

Let me know if you've come across anything similar, thanks!

[Mark Elsen]

 - Check port counters for the ports where the modbus and Scneider is connected to.

 M.

[ryero]

Hi M,

Thanks for the pointer. We checked the port counters and are getting a few input errors at the port, everything else is 0. The number of input errors are not consistent with the time-out errors, but does probably point to over utilizing the port? Even though I'm only reading 100 registers (200 bytes) every 2 seconds. I would not think that would get input errors.

I tried doing a continuous ping to the device and not get any lost packets, but still have time-out errors.

Would enabling QoS help?

[Mark Elsen]

 - Note sometimes, some of these devices (types)  can not do full duplex, check documentation and or configure port settings to half duplex , if needed.

 M.