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Public IP from Homeplug

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cbkihong

New Around Here
I have 3 Aztech Homeplug devices at home that have been in use for more than 10 years without major problems. The units are connected to gateway router, TV and network printer respectively, and properly paired when initially installed. The home network configuration and power cabling have not been changed for years, but I ran into a weird scenario today.

WAN ---> Router ----> HomePlug 1 <======> HomePlug 2 <----- Printer

The symptom is I suddenly could no longer connect to the network printer from within the LAN using the static internal IP assigned to the printer. The LAN LED kept flashing so I was pretty sure the link was up and not a dead LAN port on the printer, so I grabbed a laptop, disabled the wireless and inserted the LAN cable from the homeplug to the laptop (instead of printer), and did a DHCP renew. Voila, I got an IP, but it was actually a public IP address, and different from the one I have on the home gateway router WAN connection!

The public IP allocated to my laptop through the Homeplug is from the same internet service provider as the one I subscribe to, and actually has an identical subnet (and mask). I started wireshark and enabled promiscuous mode, saw a large volume of broadcast from some Huawei switch I believe to be from the building network hub. That was really a lot of network broadcast.

So I tested by moving the Homeplug to other sockets at home, found 3 of them exhibiting the same issue with a public IP assigned. The rest, such as those in rooms did not have such an issue, and the expected LAN IPs were assigned. I also tried to swap that Homeplug with another one I know did not have the issue, but it started exhibiting the same after plugging to those 3 sockets. So, I believe the Homeplug units themselves should not be at fault.

So there leaves several questions :-

1. How could a public IP address have been assigned? The WAN cable from broadband provider was only inserted in the home gateway router. If a specific Homeplug cannot join the rest of the Homeplug network and thus no network connection, how could it have obtained a public IP address by DHCP (it doesn't seem that it obtained it from the home gateway router)?
2. Any chance neighbors messing with their home network or power configuration could have an impact here? Does that sound fixable?
3. I did not gain access to the WAN of my neighbor, I suppose?
 
If you did a packet capture, you should be able to see the DHCP session where the public IP address is being assigned and see the IP address of the server assigning it.

If the encryption key/password is the default, try changing it.

How does your router get its WAN connection?
 
In terms of packet capture, yes, I did managed to capture the DHCP offer packets and believed it belongs to the broadband provider's network as I initially guessed. What is weird is how that can be accessed from my homeplug.

I'm not sure how router gets the connection. The broadband provider did give us a router-like device with a LAN cable in (from the wall jack) and another one out which they plug into our home router. That device is not accessible to us. I have tried cutting power supply to it as well and could still get the public IP from the homeplug, so should be unrelated. From my home router's point of view it should be just simply DHCP without requiring dialup (not PPPoE, for example).

So which encryption key / password were you referring to?
 
Use the "Simple Connect" buttons to change the encryption key.

The only explanation I can come up with is someone installed a HomePlug adapter somewhere on that switch your packet capture saw.
 
Homeplugs are Layer 2 devices, similar to an unmanaged switch...

They don't have IP's...

That being said - like @thiggins mentioned above - force a rekey on the homeplugs...
 
Thanks so much for pointing me in the right direction. Previously I tried resetting and then re-pairing the HPs using the simple connect button - that didn't help, ultimately I resolved that by using the Aztech Homeplug AV utility to manually override the "Private network name" of each unit one by one, and resolved it that way. My understanding was the simple connect would have the encryption key regenerated, but apparently that was not the case for me.
 
The Simple Connect buttons should have worked. But glad you figured out how to use the utility... and that there was one to use! Some HomePlug products don't ship with utilties.
 

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