A strange tale of Sky Fibre and accidental DSL theft

(this post is cross posted from the Sky User forums)

Hi there,

I've recently moved into a new place and transferred my existing Sky account over. This included TV and Fibre Unlimited. The old setup was a SR101 and an OpenReach modem (Huawei). The Home Move team sent out an SR102 to be used after the line was setup.

The SR102 worked ok and eventually the connection sped up to 38/9. However, it would constantly drop active connections. Not the DSL connection, but at the IP level. Large uploads would bail out after 30-50meg or so.

This, and that the WiFi on the SR102 was 2.4Ghz only, lead me to get an Airport Extreme. I had an OpenReach modem from the previous installation. I read the guide, sniffed the username/password combo for the DHCP Client identifier and setup the Airport Extreme by manually editing the configuration XML.

The connection worked - however ping times were a bit longer than previously and the connection was only running at 11/1. I plugged the SR102 in instead of the Airport extreme (so still using the OpenReach Modem) and the speed was back at 38/9. I set up the Airport Extreme again to see what was going on.

A traceroute to 8.8.8.8 was far longer than it should have been and seemed to be going through BT Internet's network. How bizarre.

The Airport extreme was reporting an external Sky IP, but when I typed 'what is my ip' into google, I got a BT Internet IP address. Puzzled, I port mapped the IP, which reveal a HTTP port.

Browsing to this IP (which I had just one hop to on mtr) revealed a Netgear router login� I have no Netgear kit. I used the default password for that brand of router and was greater with� the configuration page for my neighbour's router. I noticed the SSID as their's. At this point I was wired into the Airport Extreme and had WiFi off on my laptop. I don't know their wireless password so there was no way I was connected via Wifi.

Somehow, the airport express was routing through the Netgear router via the cabinet! This was also somehow exposing the Netgear router to me - I could connect on 192.168.0.1 also.

I changed the subnet on the Airport Extreme to something other than 192.168.0.x and rebooted. The connection is now at full speed and reporting a Sky IP address.

I think as the Airport Extreme was also setting itself up on 192.168.0.1 and setting it's DHCP clients router addresses as 192.168.0.1, there was some funky ARP going on which lead to the clients routing via the Netgear router (hitting the Airport Extreme and OpenReach box along the way). I'm also wondering if this issue was leading to connections dropping.

Is there anything I can do to stop the Netgear router 'leaking' via the cabinet? Quite friendly with the neighbour but probably a bit complicated to explain what's going on! Any advice or better explanation appreciated.

Edited by deleted (Fri 15-Aug-14 12:43:51)

Each VDSL2 connection is over a PPPoE tunnel, hence the username and password and so other uses traffic or ports should not be visible.

Also Netgear routers by default have their WAN remote configuration ports closed, so unless the neighbour had configured this way, the most likely is that you were coming in via their LAN side.

You aren't using HomePlugs by any chance? A small chance if you both have the same encryption that the two LANs may be talking to each other.

Another reason it looks more like a LAN bridge issue, is that the airport extreme should not be bridging LAN IP range traffic over its WAN port, i.e. if neighbour has 172.17.17.x as their range and you do, then even if you connect the two routers WAN ports directly, the two LANs should not see each other. Routers are meant to keep LAN traffic on the LAN side, not go searching over the WAN port for that IP range too.

In reference to www.skyuser.co.uk/forum/sky-broadband-fibre-help/56615-strange-tale...:

A helpful person on another forum has diagnosed the issue!

I extend my Wifi with a TP-Link homeplug/powerline extender. My neighbour must also be using them.

So the problem isn't at the cabinet, it's on the power lines.

I'll try repairing them.

Yes, it must have been the HomePlugs. I've re-paired them and I don't seem to have access to the neighbour's network any more.

Have you reverted to 192.168.nnn.nnn?

In reply to a post by MrSaffron:

Each VDSL2 connection is over a PPPoE tunnel, hence the username and password and so other uses traffic or ports should not be visible.

Sky (and TalkTalk I believe) don't use PPPoE - just look at a Sky router in VDSL mode. Their ADSL network uses PPPoA now most of the time. (Some areas might still be on 'MER').

Routers are meant to keep LAN traffic on the LAN side, not go searching over the WAN port for that IP range too.

Plenty don't sadly. Egress filtering is missing in most domestic routers, relying on ISP core routers to do it. Many network and server techs have never heard of it either (Sob!).

10 years ago I remember being able to traceroute to an RFC1918 address when directly plugged into an NTL cable modem from my PC, and it would route all the way to the core, which would eventually drop it.

In reply to a post by cooberto:

Yes, it must have been the HomePlugs. I've re-paired them and I don't seem to have access to the neighbour's network any more.

The default passcode is probably the same as 90% of HomePlugs use the same base Qualcomm/Atheros chip.

This is why you get the push button pairing feature, and if you install the PowerPacketUtility you can invent your own password for each plug. (You can also see link status information).

A LAN router most definitely should keep LAN traffic local. It will not route anything over the WAN port that is in the local subnet.

A modem is a totally different prospect as the modem will likely have a single IP and therefore anything outside of it is considered to be WAN.

It is nothing to do with egress filtering and merely a standard IP implementation.

In reply to a post by ian72:

It is nothing to do with egress filtering and merely a standard IP implementation.

You hope, but I've seen RFC1918 addresses routing through home routers with basic NAT. I wish it wasn't true. On a netgear box at work (on an ADSL line) I ended up using outbound filtering rules. Poor firmware quality I assume.