Hi Guys,
This is a newbie! I configured a destination NAT on the WAN interface to a specific IP address on local LAN. The problem is that the requests (UDP) which come in have the local IP address of Microtik router!

I want that the source IP of the natted packets remain unchanged.

Appreciate all comments,
-- Afshin

It sounds as if you also have source NAT/Masquerade affecting the traffic heading to the internal network. Try posting your NAT rules.