I2c two way communication between due's

hi guys,
this is nag,i am trying communicate between two due boards and it is not working.but the same code working in uno.And also i am trying to communicate between due and mega ,but due receives data but not sending ack.
please tell me how to avoid this problem.

Can you please share your code. It will be helpful for the experts to help you out.. And also, it will be helpful for the learners to understand the concepts.

Regards,
S. Sudharsan