It's pretty hard to tell from your post, may be you can add some more details? like more complete code, and the ip, port bindings? The fact you're getting an ack back from 127.0.0.1 indicates you are really talking to yourself, at first I thought may be it is a dns problem (like having a host entry to point to your self) or a route problem (like setting the gateway to yourself, in which case you shouldn't get an ack). Anyhow, I would doubt it is a perl problem, mostlikely some parameters in your code or your network setup. But that's just a guess.