What happens if I send a UDP packet to "0.0.0.0"?

main.go

package main

import (
	"fmt"
	"net"
	"time"
)

// Add an alias 127.0.0.2 to your lo0 with the following command (macOS) first:
// macOS
//  $ sudo ifconfig lo0 alias 127.0.0.2 up
// linux
//  $ sudo ifconfig lo add 127.0.0.2 up

func listen(address string) (net.PacketConn, chan struct{}, error) {
	conn, err := net.ListenPacket("udp4", address)
	if err != nil {
		return nil, nil, err
	}

	fmt.Printf("listening on %s\n", conn.LocalAddr().String())

	closeCh := make(chan struct{})

	go func() {
		for {
			buf := make([]byte, 1500)
			n, from, err := conn.ReadFrom(buf)
			if err != nil {
				close(closeCh)
				break
			}

			fmt.Printf("%s received %d bytes from %s\n", address, n, from.String())
		}
	}()

	return conn, closeCh, nil
}

func main() {
	conn2, closeCh2, err := listen("127.0.0.2:1234")
	if err != nil {
		panic(err)
	}

	conn1, closeCh1, err := listen("127.0.0.1:1234")
	if err != nil {
		panic(err)
	}

	conn3, closeCh3, err := listen("0.0.0.0:0")
	if err != nil {
		panic(err)
	}

	toAddr := &net.UDPAddr{
		IP: net.ParseIP("0.0.0.0"),
		//IP:   net.ParseIP("127.0.0.2"),
		Port: 1234,
	}

	for i := 0; i < 10; i++ {
		n, err := conn3.WriteTo([]byte("Hello"), toAddr)
		if err != nil {
			panic(err)
		}

		fmt.Printf(">>> sent %d bytes to %s\n", n, toAddr.String())
		time.Sleep(50 * time.Millisecond)
	}

	time.Sleep(1 * time.Second)

	conn1.Close()
	conn2.Close()
	conn3.Close()

	<-closeCh1
	<-closeCh2
	<-closeCh3

	fmt.Println("Done")
}

Linux:

• Packet sent to 0.0.0.0:1234 is always received by listener on 127.0.0.1:1234
• If remove the listener on 127.0.0.1:1234, the packet sent to 0.0.0.0:1234 is received by listener on 127.0.0.2:1234

Mac:

• Packet sent to 0.0.0.0:1234 is only received by listener on 127.0.0.1:1234
• Even the listener on 127.0.0.1:1234 is removed, the packet sent to 0.0.0.0:1234 is NOT received by listener on 127.0.0.2:1234