Early in this thread you mentioned these are on different network subnets. . . Just thought about a similar issue. . . sysctl -a | grep rp_filter If a packet comes in to Linux and the path BACK to the remote IP is NOT out that same interface (asymmetric routing) the Linux kernel will drop the packet. “rp_filter” controls how Linux behaves regarding this. Please provide real `ifconfig` and `route -rn` and `tcpdump port 69` output to properly diagnose. . .