Issue with DHCP and IPv4 addresses - some websites not found

[jezzer]

Hi folks

I'm having some weird issues with access to certain websites, eg. hl.co.uk. I've had this once before, last year. After a long time on the phone with BT, it was resolved. The engineer was surprised at the fix and now I can't remember what it was. It's frustrating, as some websites are accessible and some aren't. I think it may be an IP4 vs IP6 issue, but my tech knowledge of IP6 is low. Hope someone can help.

Anyway, as I say I've been having issues accessing some websites while others are fine. This happens on two Windows PCs (one is Windows 10 the other Windows 11) but does not happen on an old Mac and is also fine on my iPhone.

I have had a look at my ipconfig (using CMD) and it shows the following IP4 settings: -

IPv4 address: 169.254.226.121

Subnet mask: 255.255.0.0

Default gateway: 192.168.1.254 (which is the correct address for my BT Smart Hub 2)

I recognised that the IP address and subnet mask were wrong, so assumed DHCP isn't working correctly for some reason. I then set my IP address to static, as follows: -

IPv4 address 192.168.1.2

Subnet mask: 255.255.255.0

Default gateway: 192.168.1.254 (no change there)

DNS Servers: 8.8.8.8 (Google) and 1.1.1.1 (Cloudflare)

When I did this yesterday, everything sprang back to life, websites that hadn't been accessible suddenly were. However this morning, I'm back to where I was before setting a static IP address and, weirdly, when I do an IPCONFIG check, the address details shown for my WiFi adapter as back to the first set shown above, even though a check in Windows under Network Connections shows my static IP details as I set them.

Looking at WiFi status, I get: -

IPv4 - No Internet access

IPv6 - Internet

The only change I've made recently is to add a WiFi extender, which connects wirelessly to my Smart Hub and then runs an ethernet cable to an 8-port switch which connects a NAS drive and some home heating hubs into the network. I have tried switching all this off but it makes no difference.

I've rebooted the Smart hub several times and have even done a factory reset on it.

Any idea what might be the issue and how to fix it?

Many thanks in anticipation.

Jez

[jezzer]

BTW, I've looked at Parental Controls on MyBT - they are disabled.

[WSH]

An address starting 169.254 is an APIPA address used by Windows to give the host a temporary address when it fails to get one from DHCP.  (The idea being that if the whole network has failed, the hosts on APIPA addresses can at least carry on talking to each other.  Unfortunately, in this case it puts your computer into a separate network on its own and so it can’t talk to anyone else).

The issue is, what is stopping it getting an address from DHCP?  I would say it was the notorious DHCP on the Smart Hub 2 running out of address space but you say you have done a full factory reset, which should have fixed that.  (When you say you did a factory reset, you did hold the reset pin in until the light on the SH2 turned green again, didn’t you.  A factory reset can take a bit longer than some people realise.  The button needs to be held down for about 30 sec).

If the reset went OK then the question is what is stopping the computer seeing DHCP?  Use Ipconfig /all in a command prompt to see what it has as the DHCP address it should be using.  Is the address correct?  It could be something is blocking the discover broadcasts, so that intermediate switch would be my main suspect.  I suggest you try restarting the switch.  (Sometimes they do crash).  If that doesn’t work try bypassing it and see what difference that makes.

[jezzer]

Hi

Thank you for the quick reply. 

Yes I did a full factory reset. The light went green and the network name and default password were reinstated. 

If I understand you correctly, the PC’s DHCP address is the one given to the PC by the router when DHCP is enabled. I gave this in my initial thread. Please let me know if I’m misunderstanding you. 

What I’m at a loss to understand is why, according to ipconfig, it’s adopting this address and subnet mask, when I’ve assigned it a static IP address and DNS server addresses in Windows. As I mentioned, when I look at the WiFi configuration in Windows, it shows the static IP details I gave it.  Why would those details be different to the details that ipconfig shows?

Also, to clarify, my PC is connected directly to the SH2 via WiFi. The switch is connected to the SH2 via an Ethernet cable plugged into a WiFi extender, due to a thick wall that I can’t easily drill through. So I doubt the switch is the problem. 

I might have a look at the IP address table, to see how full it is. As you suggest, I doubt it’s full. 

thoughts on the above questions welcome!

cheers

Jez

[WSH]

The wired and wireless addresses are separate, (although usually relate to the same network).  It’s quite possible to set a dynamic address for the WiFi connection and a static address for the wired.

As I said, 169.254 is an autoconfigured address set by the computer itself when it can’t get a reply from DHCP.  It sounds as though you’ve failed to set up the wired NIC properly.

[jezzer]

Hi

Neither Windows PC has a wired connection. Only WiFi. Neither is connected to the switch.

i only mentioned the switch because I’d recently added the WiFi bridge/extender that it’s plugged into and initially wondered whether adding that had buggered things up. However I’ve tried switching all that off. Didn’t help. 

thoughts welcome  

Thanks again

Jez 

[WSH]

It sounds as though the static address you’ve set clashes with the address being used by something else.  That may cause it to drop back to APIPA.   Try changing the static address to something else. 

[jezzer]

I’ll have a look, but I believe the DHCP range is set from .64-.253 and I’ve assigned my PC .2. 

it has been coming up with an error suggesting there are multiple default gateways on the network, when I assign the static IP address to my PC. There isn’t another, unless another device is trying to behave like one. Is that a clue?

[WSH]

Well, speaking as a retired IT tech, this sounds like one of those situations where there is a misconfiguration/clash with something else, somewhere.  Unfortunately, it often takes a bit of head scratching to pin-point, at which point it will be something blindingly obvious.  Sorry I can't be more helpful.

[jezzer · Accepted solution]

Hi

Just thought I'd loop back and show the solution to this issue. Amazingly ChatGPT guided me to diagnose and fix it!

https://chatgpt.com/share/6866ecc2-9100-800a-a474-9d7881b58cd7

Enjoy!

Cheers

Jez