I've written a UDP Server in Go(listens on port 666), and it seems to be only receiving packets that were sent locally. To confirm traffic, I have been using: My(abbreviated) server code: If, from the machine the server is running on, I use: then the server receives that packet, and prints the message(and tcpdump shows no output). However, if I

Golang UDP Server only recieving locally sent packets

I’ve written a UDP Server in Go(listens on port 666), and it seems to be only receiving packets that were sent locally. To confirm traffic, I have been using:

sudo tcpdump -n udp dst port 666

My(abbreviated) server code:

import "net"

func startServer() {
    // Bind the port.
    ServerAddr, err := net.ResolveUDPAddr("udp", "localhost:666")
    if err != nil {
        fmt.Println("Error binding port!")
    }

    ServerConn, _ := net.ListenUDP("udp", ServerAddr)
    defer ServerConn.Close()

    buf := make([]byte, 1024)
    for {
        // Recieve a UDP packet and unmarshal it into a protobuf.
        n, _, _ := ServerConn.ReadFromUDP(buf)
        fmt.Println("Packet received!")
        // Do stuff with buf.
    }
}

If, from the machine the server is running on, I use:

echo -n “foo” | nc -4u -w1 127.0.0.1 666

then the server receives that packet, and prints the message(and tcpdump shows no output).

However, if I run the following from another computer on the network:

echo -n “foo” | nc -4u -w1 192.168.1.134 666

Then, while tcpdump reports a packet being received (15:05:43.634604 IP 192.168.1.113.59832 > 192.168.1.134.666: UDP, length 9 confirming I got the IP address right), the Go server does not respond.

Is there something special I need to do to make Go respond to non-local requests?

Answer

Just listen on any address, you’re listening on localhost only.

ServerAddr, err := net.ResolveUDPAddr("udp", ":666")

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Answer