This topic

PRIVATE IP OUTSIDE OF PRIVATE DHCP SCOPE COMMUNICATING WITH MY LAN

Sambob — Thu, 17 Aug 2023 10:55:40 GMT

I'm on BT's FTTP using a BT Smart Hub 2 including BT Voice.

I use the home hub as the authorative DHCP server. The Hub's IP is default 192.168.1.254 subnet 255.255.255.0

The DHCP scope is allocating IP's on Private class C network 192.168.1.64 - 192.168.1.240 (/24 subnet)

I used DHCP for most devices and all devices have subnet 255.255.255.0 (/24 subnet) This should mean that communication on my LAN should be locked within the DHCP scope.

I've recently done a network audit on my LAN using netscan and have been alarmed by an IP that is present outside of my IP range (192.168.201.15) and is able to communicate with my network. I can see this IP in netscan, however, it doesn't present a MAC address. I am able to ping this address.

I know this is a device outside of my LAN as when I unplug power to my router the ping response times out.

Naturally I'm concerned about this and am reaching out for any help advice avaivable.

Re: PRIVATE IP OUTSIDE OF PRIVATE DHCP SCOPE COMMUNICATING WITH MY LAN

WSH — Thu, 17 Aug 2023 13:49:36 GMT

I doubt it’s anything to worry about. Anything with 192.168 won’t pass through routers across the internet, so it is something internal to your network.

It’s quite common practice in industry to give the management interface on equipment, (like managed switches, for example), an IP in a different subnet to stop the ordinary user stumbling across them and playing with them. I suspect this is something similar. Possibly a piece of equipment connected through the switch built-in to the router or maybe even the router’s own management page? That’s why it disappears when you shut down the router.

If it’s something to do with BT equipment I’m sure one of the more knowledgeable guys will jump in and explain it better than me.

Re: PRIVATE IP OUTSIDE OF PRIVATE DHCP SCOPE COMMUNICATING WITH MY LAN

Sambob — Thu, 17 Aug 2023 14:17:30 GMT

Thanks for the reply. The IP (192.168.201.15) outside of my inernal range is 100% not assigned to any of my internal equipment neither is it the BT Smart Hub 2's IP - This is the default 192.168.1.254/24 as mentioned in OP.

It is definately outside of my LAN and I suspect perhaps another client/customer of BT who has set a more open subnet (broadcast?) allowing communication over WAN with my range.

If it is BT's equipment it is odd they would set it to a private address within the class 3 range which is meant for private home networks. Regardless, I do not want this, or any other private IP outside of my private LAN to be able to communicate with my LAN for obvious security reasons.

I've raised with BT and they have escalated to the tech security team and am awaiting response and will report back on here if I get any meaningful explanation or resolution.

It may be that I have to buy a 3rd party router and setup access control, however, this is not completely straight forward due to using BT's Digital Voice. I may have to do some configuration on both BTSH2 and the 3rd Party router so the 3rd party router handles access control / routing, WAP, etc and the BTSH2 simply acts as a modem. Ideally I shouldn't have to do this, but will see what response I get on here and from BT.

Re: PRIVATE IP OUTSIDE OF PRIVATE DHCP SCOPE COMMUNICATING WITH MY LAN

WSH — Thu, 17 Aug 2023 15:23:11 GMT

Your concerns are noted and what equipment you run is up to you, of course. I was only trying to allay your fears. It is quite possible to run your own network, through you own router inside the SH2. I’m doing it myself because of DV.

Just to clarify, the notion of class A, B and C relates to the old Classful addressing scheme and is obsolete today. In both this and modern Classless addressing, 192.168 does not pass through a router onto the internet. If this did happen on routers it would be a major, major problem. The address conflicts alone would rapidly bring the internet to a standstill, so I doubt very much that this is from outside of your network.

That having been said, I’ll leave you to it. As I said, I’m sure someone more knowlegable will pick the thread up. All the best.

Re: PRIVATE IP OUTSIDE OF PRIVATE DHCP SCOPE COMMUNICATING WITH MY LAN

licquorice — Thu, 17 Aug 2023 15:25:48 GMT

I can't see how it can possibly be from outside of your LAN.

As @WSH has said, 192.168.xxx.xxx is not routable on the internet.

Re: PRIVATE IP OUTSIDE OF PRIVATE DHCP SCOPE COMMUNICATING WITH MY LAN

Anonymous — Thu, 17 Aug 2023 16:50:28 GMT

@Sambobwrote:
I know this is a device outside of my LAN as when I unplug power to my router the ping response times out.

A better test would be to simply unplug the ethernet connection to the ONT. That breaks the WAN connection while leaving the LAN intact. I'd wager you can still see/ping the mystery IP, showing it's internal.

Then maybe try entering it into a web browser & see if anything comes up. If not, power your devices off one at a time until it goes away.

Re: PRIVATE IP OUTSIDE OF PRIVATE DHCP SCOPE COMMUNICATING WITH MY LAN

ptrduffy — Thu, 17 Aug 2023 16:47:32 GMT

If it's showing up as 192.168.x.y on a netscan that you're running on a device connected to your hub, then by definition it is inside your LAN - as others have said 192.168.x.y addresses are not routable. The fact that it's outside your DHCP range simply means that it has been allocated a static IP address on the device itself.

Are you by any chance using powerline adapters? ISTR a recent thread where there was a suspicion of traffic leakage between neighbouring properties through inductive coupling between adjacent powerline systems.

Re: PRIVATE IP OUTSIDE OF PRIVATE DHCP SCOPE COMMUNICATING WITH MY LAN

Sambob — Fri, 18 Aug 2023 08:46:54 GMT

100% outside of my LAN. I suspect it's not on the internet, but within BT's network.

Re: PRIVATE IP OUTSIDE OF PRIVATE DHCP SCOPE COMMUNICATING WITH MY LAN

licquorice — Fri, 18 Aug 2023 08:52:47 GMT

The BT BRAS has a private address but is normally in the 172 private range but they might have also used a 192.168 address . What is the hub showing as it's Gateway address?

Re: PRIVATE IP OUTSIDE OF PRIVATE DHCP SCOPE COMMUNICATING WITH MY LAN

Sambob — Fri, 18 Aug 2023 08:59:17 GMT

Very good idea.

I unplugged the power to the ONT and the device no longer responded to ping.

Could it be the ONT itself?

Re: PRIVATE IP OUTSIDE OF PRIVATE DHCP SCOPE COMMUNICATING WITH MY LAN

licquorice — Fri, 18 Aug 2023 09:00:59 GMT

Very likely if it's not the Gateway

Re: PRIVATE IP OUTSIDE OF PRIVATE DHCP SCOPE COMMUNICATING WITH MY LAN

Sambob — Fri, 18 Aug 2023 09:18:09 GMT

Broadband IP address: 81.136.55.xxx

Default gateway: 172.16.13.191

Primary DNS: 81.139.56.100

Secondary DNS: 81.139.57.100

Re: PRIVATE IP OUTSIDE OF PRIVATE DHCP SCOPE COMMUNICATING WITH MY LAN

licquorice — Fri, 18 Aug 2023 10:19:47 GMT

If you really want to determine if it is on your LAN, very carefully unplug the fibre cable from the ONT to disconnect from the internet and see if the address is still pingable. This is at your own risk.

If it is pingable with the fibre disconnected but not with the ONT depowered, it must be the address of the ONT.

Re: PRIVATE IP OUTSIDE OF PRIVATE DHCP SCOPE COMMUNICATING WITH MY LAN

WSH — Fri, 18 Aug 2023 10:47:58 GMT

Be interesting to see the result of that. The ONT is the other side of the router WAN interface so I would still not expect 192.168 to reach it.

Re: PRIVATE IP OUTSIDE OF PRIVATE DHCP SCOPE COMMUNICATING WITH MY LAN

Sambob — Fri, 18 Aug 2023 12:03:52 GMT

Thanks for the suggestion of unplugging the fibre cable from the ONT. Good idea!

I did this and pings timed out, so this IP MUST be outside of my LAN and not the ONT itself.

Re: PRIVATE IP OUTSIDE OF PRIVATE DHCP SCOPE COMMUNICATING WITH MY LAN

countrypaul — Fri, 18 Aug 2023 12:54:28 GMT

What result do you get if you try trace root to the ip address?

Re: PRIVATE IP OUTSIDE OF PRIVATE DHCP SCOPE COMMUNICATING WITH MY LAN

Sambob — Fri, 18 Aug 2023 13:45:26 GMT

Have done a few trace routes and that IP doesn't show as a hop to external hosts either.

This private IP to me, looks like a private device within BT's network. I suspect a customer/client device with broadcast subnet.

Re: PRIVATE IP OUTSIDE OF PRIVATE DHCP SCOPE COMMUNICATING WITH MY LAN

licquorice — Fri, 18 Aug 2023 14:13:37 GMT

Yes, 172.16.13.191 is the BRAS, it can't be beyond that as it isn't routable.

Re: PRIVATE IP OUTSIDE OF PRIVATE DHCP SCOPE COMMUNICATING WITH MY LAN

licquorice — Fri, 18 Aug 2023 14:29:51 GMT

I get the same via a different BRAS.

Possibly the address of the device used to update/access BT Hubs throughout the network.

Re: PRIVATE IP OUTSIDE OF PRIVATE DHCP SCOPE COMMUNICATING WITH MY LAN

countrypaul — Fri, 18 Aug 2023 14:41:42 GMT

I also get the same result but with a different BRAS