On MAC, we used the code

    dns.HandleFunc(".", handleDNSRequest)
    defer dns.HandleRemove(".")
    // start serverUDP
    serverUDP := &dns.Server{Addr: "127.0.0.1:53", Net: "udp"}
    go serverUDP.ListenAndServe()
    defer serverUDP.Shutdown()

It bound properly on specific IP and PORT as shown below:

udp4 0 0 127.0.0.1.53 .

But as soon as we write DNS response from handler function like

    msg.Authoritative = true
    domain := msg.Question[0].Name
    msg.Answer = append(msg.Answer, &dns.A{
        Hdr: dns.RR_Header{Name: domain, Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: 60},
        A:   net.ParseIP("1.2.3.4"),
    })
    w.WriteMsg(&msg)

Binding changes to as shown below:

udp4 0 0 *.53 .

This impacts other DNS server which is running on another interface.

I debugged the UDP DNS code and figured out that after the below line is executed the binding changes

conn.WriteMsgUDP(b, oob, session.raddr)

Please let me know any more information is required such that this great code can be useful in case we wanted to bind to specific IP address and retain the binding

cc: @fastest963