I have implemented MODBUS TCP in C. The network protocols successfully implemented and tested are MODBUS/TCP/IP and ARP/IP. I am unable to connect my device (TCP/IP server-MODBUS Slave) to simulators like mbpoll etc. Kindly advise me about the other bare minimum network protocols, if any, that I need to implement in my device. The device should then be able connect to any TCP/IP client-MODBUS Master.

 

I hope this is just a student project - one problem with "Ethernet" and "Modbus/TCP", is that when customers buy it they also assume:

1) IP can be fixed or DHCP
2) A web server exists to help configure the product
3) PING/ICMP should work as expected
4) your ARP will need to handle gateways and routing.

As for your problem, use wireshark to trace both when a known-good master connects to you and to a known-good slave. There must be a difference.

Most likely your TCP/IP stack is not behaving as is the norm.