Modbus TCP out of ordeer packets, duplicate ACKs and connection problem

[sumitv]

Hi,

I am using Modscan32 as my Modbus TCP/IP Master host.
I am communicating with modbus slave over ethernet.

I configured modscan to poll the data every 5 seconds.
After some time, I saw TCP IP duplicate ACk's getting sent by slave. Modscan32 respond to these ACK's with ACK's. This process seems to be happening in a loop.

Sometime I also see "Modbus Message Overrun" message on Modscan screen.
Sometimes Modscan host sends multiple Modbus TCP packets within 1 TCP/IP packet. On the slave side I have linux TCP/IP stack and modscan32 host is running on Windows machine.

PFA Wireshark/ethereal .pcap file for the transaction.
Modbus host IP address: 192.168.1.13
Modbus Slave IP Address: 192.168.1.253

Please let me know how should I fix this.

Regards,
Sumit