We already tried "NDLB-connectile-dysfunction=true" as the client (Yealink T28P) is not using rport in its VIA header. But still no luck freeswitch still sending the response to the port in Contact header (5062) instead of the recieving port (14335). 5062 port is actually not valid as the client is behind NAT and only can get the response if freeswitch will send it to 14335 port.