I could not explain the strange NAT behavior, hope someone could help:
I have a linksys wrt54g router at home.
- Client sends UDP keep alive packet from 192.168.1.20:16688 (nat outside public IP/port is known by STUN) to a public server every 15 seconds. (public server will ignore client keep alive packets and not sending response back)
- sever sends random messages (a few packets) back to client's NAT public address/port
- client receives packets from server OK
However, client only receives messages from server once, after that client no longer can receive messages from server. I have sniffered the NAT outside link and the packets do reach the NAT. Looks like the NAT port mapping is removed even with keep alive packet send every 15 seconds.
I have tested other NAT and do not see such problem.