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Strange IPv4 problems after Full Fibre Upgrade

paulwt — Thu, 17 Oct 2024 11:24:50 GMT

I recently had a full fibre upgrade. Initially everything seemed to work fine but on restarting my PCs I got a very strange network behaviour. I could do google searches and see the results but on trying to connect to a web page it would fail with can't reach this page. This was on all browsers and both my desktop and laptop. Restarting the hub and would solve the problem. However, restarting the PC or laptop would bring the problem back. I was also no longer able to connect to the hub by typing the physical address 192.168.1.254. This was even more strange as my PC is physically connected to the hub.

I dropped into the command window and tried pinging addresses. After a hub restart I could ping everything. bbc.co.uk, www.hl.co.uk, bt.com, www.bbc.com and of course 192.168.1.254. However, when I restart the PC or laptop I could only ping things that return an IPv6 address not anything that returns an IPv4 address (bbc.co.uk but not www.hl.co.uk etc which return a could not find host) even stranger pinging 192.168.1.254 produces a fail to transmit error. Once again restarting the hub clears the problem and everything works again.

An added data point is that if I point my wireless laptop at my BT wifi extender then everything works fine for the laptop. Point it back at the hub and it stops working again. The hub has been replaced and exhibits the same behaviour. I am at a loss what to try next?

Re: Strange IPv4 problems after Full Fibre Upgrade

Christopher_G — Fri, 18 Oct 2024 14:45:52 GMT

Hi @paulwt

Welcome to the community.

That's a strange issue. We have some fantastic community members here who may be along to share their expertise.

In the meantime, it may be worth having a chat with our Technical Support team.
Chris

Re: Strange IPv4 problems after Full Fibre Upgrade

paulwt — Fri, 18 Oct 2024 21:18:01 GMT

Thanks for the suggestion. I did try the technical support team prior to the post but was told that because the PC and laptop were over two years old that they couldn't provide support. I did press on this point but they then stated that as I could do a Google search that they were providing a network connection and therefore the problem had to be with my computers.

Re: Strange IPv4 problems after Full Fibre Upgrade

Steve_M — Fri, 18 Oct 2024 21:53:07 GMT

Hi Paul,

What do you mean by "BT wifi extender"? Have you tried with that unplugged?

Steve

Re: Strange IPv4 problems after Full Fibre Upgrade

WSH — Fri, 18 Oct 2024 22:05:44 GMT

It sounds like the DHCP on the hub, which has a reputation for running out of address space and needing a factory reset to clear it, but you say you’ve changed it already. That seems to rule out the DHCP.

Next time it happens, open up a command prompt and type ipconfig /all. Take a look at the IPv4 address that has been allocated to the PC. If it starts 169.254 then DHCP is not supplying an IPv4 address to the PC, for some reason, and it’s dropping back to an APIPA address. This would stop it connecting to the hub and out to the rest of the world on IPv4. As IPv6 autoconfigures, you would not see the effect with IPv6.

If it is failing to get an address you could try giving the PC a static address. The default DHCP range, if I remember correctly, is 64 upward, so something like 192.168.1.10 should do for a static address.

If you have a switch between the PC and the hub, I’d also restart the switch.

Edit: And, while I think about it, you're not running two DHCPs are you? That can cause all kinds of trouble unless they are configured as a split scope.

Re: Strange IPv4 problems after Full Fibre Upgrade

paulwt — Sat, 19 Oct 2024 09:41:55 GMT

Hi, you are absolutely right and the IPv4 address is coming back as 168.254.10.136 (tentative). Then when I restart the hub it comes back as a valid IPv4 address and everything works again. However, on setting the IPv4 address manually I get a duplicate flagged up. I have tried a number of times with different addresses that I checked to see and they still flag as duplicates.

Re: Strange IPv4 problems after Full Fibre Upgrade

Anonymous — Sat, 19 Oct 2024 09:46:48 GMT

You need to factory reset the Hub, not just restart it to clear the DHCP table.

If you have BT DV handsets, backup contacts first.

Any address between 1 & 63 isn't in the DHCP range, so shouldn't be giving duplicates.

Make sure that all devices aren't using MAC randomisation when connected to your home network.

Re: Strange IPv4 problems after Full Fibre Upgrade

paulwt — Sat, 19 Oct 2024 09:53:51 GMT

Hi,

Thanks for the suggestion. I have done a factory last week. I was also sent a replacement hub which then exhibited the same problems. It was fine immediately after the reset but when the PC and laptop were re-booted they then got the same problem. However, I have just unplugged the BT Wifi extender and tried again. At the moment this seems to have solved the problem. Looking at the Wifi extender it appears to be a TP Link device. I will try plugging it back in to see if it then breaks it. What I don't understand is that this all worked fine until I was moved from copper to cable.

Re: Strange IPv4 problems after Full Fibre Upgrade

paulwt — Sat, 19 Oct 2024 09:57:29 GMT

Steve. I was having problems with coverage in our house so purchased a WiFi extended from the BT shop a few years ago. You just plug it in and sync it with the hub. It appears to be a TP Link manufactured device. However, I have unplugged it now and it seems to resolve the issue. This is strange as it has worked fine for a number of years and I only encountered a problem when I was switched from copper to full fibre.

Re: Strange IPv4 problems after Full Fibre Upgrade

paulwt — Sat, 19 Oct 2024 10:15:51 GMT

Hi,

I want to give a big thanks to everyone that has posted suggestions. It is very much appreciated.

So I have now plugged the WiFi extender back in and things are all working fine. So in effect restarting the WiFi extender seems to have cured the problem. I am not sure why the Extender was causing problems as it has all worked fine for a number of years. I am also wondering if the fact that it happened as I switched to Full Fibre was just coincidence or whether it was triggered by switching the hub to a full fibre connection.

I am not sure how to indicate that all the suggestions were instrumental in reaching the solution so have marked this comment and would advise anyone encountering the same problem to read through the thread.

Once again thanks to everyone for your help.

Re: Strange IPv4 problems after Full Fibre Upgrade

WSH — Sat, 19 Oct 2024 10:40:51 GMT

Strange indeed.

It sounds suspiciously as though the Wi-Fi extender has its own DHCP. That wouldn't cause a problem until it just happens to allocate an address that the hub has already allocated to something else. Quite often in that situation, the network grinds to a halt while the two devices argue. If it does have a separate DHCP, there will be a management interface for it on the Wi-Fi extender. I'd go into it and turn off the DHCP, if I were you.

Re: Strange IPv4 problems after Full Fibre Upgrade

paulwt — Sat, 19 Oct 2024 14:48:56 GMT

I connected to the WiFi extender and it does have a DHCP setting. Currently it is set to automatic with alternative options of On and also Off. If I set it to off will that not prevent devices connecting to it?

Re: Strange IPv4 problems after Full Fibre Upgrade

WSH — Sat, 19 Oct 2024 18:25:10 GMT

Ah, that will just be for where it gets an IP address from. Leave that on.

I was talking about an second DHCP, issuing addresses to other devices.

Under the circumstances RBZ5416 would seem to be right. It sounds like MAC Randomisation on mobile devices. The idea was to protect you from tracking by issuing a new MAC address everytime the device connected. The trouble is DHCP will see it as a new device each time and issue a new IP addresss, eventually running out. The hub then needs a factory reset to clear it. I'd turn off MAC randomisation on your phones etc., as it was really intended for privacy on public hotspots. In the real world, it's a nice idea on paper and a pain in the ... on domestic networks. Unless you are really paranoid about tracking, turn it off on each device.

You've not got half a dozen kids with smart phones have you? That will soon use up the available addresses. LOL.

Re: Strange IPv4 problems after Full Fibre Upgrade

Anonymous — Sat, 19 Oct 2024 19:10:49 GMT

W11 also has MAC randomisation that should also be turned off.

Re: Strange IPv4 problems after Full Fibre Upgrade

WSH — Sat, 19 Oct 2024 19:28:08 GMT

Good point but not necessarily, it would seem.

I've just check my 3 year old Win 11 Pro laptop and that setting is not there. I suspect it depends on the capabilities/age of the network card. Mine's only 802.11ac.

Re: Strange IPv4 problems after Full Fibre Upgrade

Anonymous — Sat, 19 Oct 2024 19:43:00 GMT

@WSH

Odd, my Lenovo is four years old, also with ac. I thought it was baked into Windows rather than hardware dependent.

https://support.microsoft.com/en-gb/windows/how-to-use-random-hardware-addresses-in-windows-ac58de34-35fc-31ff-c650-823fc48eb1bc#WindowsVersion=Windows_11

Re: Strange IPv4 problems after Full Fibre Upgrade

WSH — Sat, 19 Oct 2024 19:56:59 GMT

Very odd?

I've never seen it on Win 11 but I'm mostly a hardwired man anyway, so the whole Wi-Fi thing is usually not there. I suppose it's implementation is inevitable if other manufacturers are doing it but it's definitely not present on my Acer X515EA.

Just for reference, is that setting on or off by default?

Re: Strange IPv4 problems after Full Fibre Upgrade

paulwt — Sat, 19 Oct 2024 20:10:23 GMT

I can turn the MAC randomisation off. However, I did do a hard reset of the hub and it didn't clear the problem. I also had the hub replaced and the new one immediately started to exhibit the problem. However, restarting the WiFi extender does seem to have cleared the problem. To clarify the extender had been in for a number of years with no problems and the continued to work throughout. The Smart hub also worked fine until the switch over to full fibre when it started to exhibit the IPv4 problem. I am pleased the problem has gone away and if it returns I will just restart the extender again but not really sure why it occured and whether it was just a coincidence that it happened at the same time as the fibre switch.

Re: Strange IPv4 problems after Full Fibre Upgrade

WSH — Sat, 19 Oct 2024 21:18:16 GMT

Yes, it’s a strange one.

With changing/restarting something like the hub it is possible that it confused the extender and it retained the old network settings, causing a clash. Those sorts of problems don’t always happen with a restart but I have come across similar before. It can be a good idea to restart the other network devices after the hub has been restarted. I take it you restarted the hub and then the extender after the new ONT was up?

Sorry, at this point, I’m out of ideas. If it works now, I suggest you just see how it goes.

Re: Strange IPv4 problems after Full Fibre Upgrade

Anonymous — Sun, 20 Oct 2024 07:34:03 GMT

@WSH

I believe it was on by default as I recall switching it off. But if it is indeed hardware dependent, then I guess it could be up to the hardware manufacturer to make that choice?