I had a very weird experience recently that I'm trying to debug in my home network.
I was on my mac looking at the computers on my home network that were auto-discovered. I saw a computer I didn't recognize, which spooked me a bit. I was able to access that rogue computer's files. I was connected via password protected (WPA2) wifi at the time to my own network.
I then ran a traceroute to determine what was the first hop to any ip address. It turns out the first hop was not my own router. Instead it was a neighbor's wifi router. I was very surprised.
Here is my home setup:
Cable Modem for internet, plugged into WAN of Buffalo 300N router (with DD-WRT firmware). The 2 of the LAN ports on the router are in use: 1 for a desktop computer and 1 other for a Powerline device (an Actiontec MegaPlug A/V 200). Upstairs I have an output for the Powerline networking, which is a TrendNet device with 3 RJ-45 female connections, one of which is in use connected to my Panasonic TV for the purpose of streaming Netflix faster than Wifi affords.
While debugging why I was connected to someone else's router on my own network I noticed a few things:
- If I unplugged the powerline device from my router's LAN, my internet would die.
- If I unplugged the cable modem from my router's WAN, my internet connection would persist fine.
- When visiting 126.96.36.199, I was presented a login screen for my neighbor's Linksys E1000 router, instead of my own admin screen.
- When I power cycled everything and did an ipconfig /refresh on all my computers, I was connected back on my own network, but now my neighbor's computer was on my network (instead of my computers on his network).
My router was not configured to be in bridge mode. My only logical conclusion is that my router lost a DHCP war with my neighbor's router, and my neighbor must also be using a Powerline device in his home network. We live in an apartment building, so it's conceivable that the Powerline is jumping apartment units.
So my question: is my own conclusion correct given the symptons? If so, what can I do to prevent my neighbor's router from winning this DHCP battle, while still using Powerline networking in conjunction with my wifi router? Any advice on how to secure my network and not accidentally connect to my neighbor's network again?