Most users are surprised, when they try replaying UDP traffic over loopback, that the listening daemon never sees the traffic. This turns out to be a limitation of the loopback interface on many operating systems. One contributing factor may be capturing traffic on an Ethernet port, rewriting the IP addresses but not the L2 header. Since the loopback interface doesn't use an Ethernet L2 header, the IP stack of the operating system is unable to parse the packet and deliver it to the listening daemon.