Oh heck, IPv6. That's been mostly nuked from orbit hereabouts. I say mostly because I don't have that capability on my android devices, my slab has an IPv6 address so an IPv6 connection should be achievable between that and either end of the powerline, wouldn't it?
The ASUS documentation on this is rubbish I just had a quick look.
You found something? Where's the manual was question 1 to Asus. All they came back with was the quick start guide.
I can see how it doesn't need an IP address to do the over-powerline part. Whatever comes in one end just gets encapsulated and transmitted to the far end for retransmission. I've built RS232 over mains devices, that was just a crude media converter (college project). In my professional life I designed fibre extenders for a rack based system with parallel backplane data. Encapsulate, transmit, reform. Serial peer to peer comms in that system was like an onion, each layer having it's own addressing, error detection, sequence numbers etc wrapped around the data. What was just data at one layer was addressing, error detection, sequencing and data at the next.
nmap scans from a client return the mac address of my router and clients are registered in my router DHCP so it's not faking itself in place of my router.
Responding rather than passing through is something different though, the browser has to be sending out an IP it wants to communicate with if I'm understanding the higher layers at all. I get how the powerline kit can watch for a specific DNS request and reply itself rather than forwarding those packets. Could it reply with an internet address? Pretend to be a device beyond my router and go on intercepting http(s) requests to that address? That would explain how it can be talked to without appearing in my local IP range. Is that what iddu is describing? I can't packet trace anything until I can pursuade the damn things to respond to the initial request.
Perhaps I need to play dumb to get started. My network uses VLANs and as said IPv6 is killed, there may be other settings having an effect. I have an old router, perhaps I factory reset that, give it the minimum settings needed to get online and try that way. Sound worth a try?