Strange IPv4 problems after Full Fibre Upgrade

[paulwt]

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?

[Christopher_G]

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

[paulwt]

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. 

[Steve_M]

Hi Paul,

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

Steve

[WSH]

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.

[paulwt]

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.

[rbz5416]

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.

[paulwt]

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.

[paulwt]

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.

[paulwt · Accepted solution]

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.