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BT DNS Server Problems

GerMarsh — Mon, 03 Mar 2025 11:45:29 GMT

Hello BT Community - thank you for allowing me to join.

I have been helping an elderly neighbour in setting up a new PC. He only wishes to use email and do some web surfing so that bit was quite easy.

He called late on Saturday as he was unable to access his email. He immediately thought that the problem was with his PC.

I called in on him yesterday morning and encountered an interesting situation. (I am no network specialist but many decades doing IT support and consultancy have allowed me to pick up a few things!)

To cut a very long list of diagnostic steps short, the problem lay with the DNS servers configured on his home hub to be pretty useless inasmuch as they were not translating domain names, neither IP4 nor IP6 from what I could tell. I could not find out how to change the DNS names too - they are 81.139.56.100 and 81.139.75.100. They did not respond to pings but I assumed that was a deliberate ploy. The neighbour did not think that the fault lay with the home hub as "the blue light is on". Changing the Windows11 primary DNS server to 8.8.8.8 resulted in everything working as it should.

There was nothing obvious in the error log on the router so, I reluctantly rebooted the thing. This resulted in everything working again.

At home we have a couple of Mikrotik devices - mainly as we have a rubbish landline speed in West Wales - and many routers (mainly acting as ethernet hubs) including tp-link and old home hubs. I cannot ever remember encountering a situation where the broadband link is ok but the dns service is dead.

It is sorted now but any information would be gratefully received in case it happens again. Also, is there any way to alter the DNS server addresses on the home hub? I suspect not.

Thank you in advance,

Gerald.

Re: BT DNS Server Problems

Rach_H — Wed, 05 Mar 2025 09:02:48 GMT

Hi @GerMarsh,

Welcome to the Community!

I'm so sorry to hear about the trouble your neighbour has been having, but it's great to hear he has you to support him with any issues he has, and that you've been able to get him back up and running.

As the issue is now resolved it would be tricky to pinpoint the cause. However, if he does have this same issue again then give our team a call, and they will be happy to run through some diagnostics.

Rach

Re: BT DNS Server Problems

wuxmedia — Mon, 17 Nov 2025 17:24:31 GMT

I seem to have the exact same issue as the OP.

Sometimes DNS just breaks down, the connection is not broken, as per the elderly person in the OP, the blue light is on.

I can ping 8.8.8.8 fine - pinging anything with DNS fails. This affects all the devices connected and eventually everyone in the house starts to complain about a lack of connection.

I have the same DNS server IPs as the OP and they do not ping, maybe they are blocked, that makes troubleshooting hard.

It usually comes back by turning the hub fully off and back on again (classic), which shows the exact same DNS server IPs again so perhaps isn't that at fault.

I will try altering the the local DNS as per the OP - which is a good idea, instead of polling the hub. But same as the OP - I've not seen this before and I'm not sure my family would enjoy diving into their device settings.

Re: BT DNS Server Problems

GerMarsh — Mon, 17 Nov 2025 18:28:07 GMT

Hello Wuxmedia,

I think I altered the DNS on the BT Hub and not on his PC.

Re: BT DNS Server Problems

licquorice — Mon, 17 Nov 2025 18:43:09 GMT

You certainly didn't, it is not possible to change DNS servers on the BT hub

Re: BT DNS Server Problems

wuxmedia — Mon, 17 Nov 2025 19:20:11 GMT

Indeed, it's not possible to change them in the hub, I think this should work for me (although I'm on a Mac, same thing)

Changing the Windows11 primary DNS server to 8.8.8.8 resulted in everything working as it should.

Which just makes me wonder what is happening with the hub. It's all stock config basically, I turned 5g off that's about it.

Re: BT DNS Server Problems

WSH — Mon, 17 Nov 2025 19:31:03 GMT

I might be giving in to conspiracy theories here, but since the IPA, (Investigatory Powers Act), obliged ISPs to keep track of where people have been browsing for up to 12 months, one way to do it discretely would be logging DNS lookups.

Re: BT DNS Server Problems

GerMarsh — Mon, 17 Nov 2025 19:33:06 GMT

You are absolutely correct, Licquorice.

I even checked with my ancient Home Hub 3 (now relegated to being an Ethernet hub) and that doesn't have it either.

Sorry, I am used to MikroTik kit these days.

(However, we - in wild west Wales - have been informed in the last month that we have full fibre available. I may have to go back to the nailed down "consumer" routers again.)

Our original Broadband service was pretty **bleep**e. It would fail every evening and, after around 15 Openreach engineers failing to fix, we went with a 4G solution. It has been brilliant, to be fair. Mainly because we have line of sight to the cell tower.

(Sorry - I digress!)

Re: BT DNS Server Problems

licquorice — Mon, 17 Nov 2025 19:38:41 GMT

You only need the BT SH2 if you require Digital Voice, otherwise you can stick with MikroTik

Re: BT DNS Server Problems

wuxmedia — Mon, 17 Nov 2025 19:42:24 GMT

one way to do it discretely would be logging DNS lookups.

Ideally DNS would work though to do that lol.

Tin foil hat on : It does track though, as I've only seen it have this issue recently.

Looks like I'll be checking some guides out about breaking ties with the hub

Re: BT DNS Server Problems

CanardNoir — Mon, 17 Nov 2025 19:42:36 GMT

There does seem to be an ongoing and unacknowledged problem with BT's DNS servers. I've had similar issues to those the the OP describes (though mine were not connected to email).

Changing the DNS address to 8.8.8.8 (on all my devices, since you can't change it on BT's hub) solves the problems.

There are even problems getting to Microsoft's sites using BT's network - some obscure routing problem and no way of telling anyone there so they can investigate it (one is met with disbelief and intellectual "snobbery").

BT's DNS servers don't respond to pings (or trace route attempts) by design and that is quite a sensible solution for them even though it makes diagnosis harder for its customers.

I'm going to leave all my devices set to 8.8.8.8 now because despite being (or once was) the UK's premier telecom provider they appear to no longer be focussed on giving an excellent customer experience and, I assume, now pursue other goals.

Re: BT DNS Server Problems

licquorice — Mon, 17 Nov 2025 19:50:54 GMT

@wuxmediawrote:
one way to do it discretely would be logging DNS lookups.
Ideally DNS would work though to do that lol.
Tin foil hat on : It does track though, as I've only seen it have this issue recently.
Looks like I'll be checking some guides out about breaking ties with the hub

Just use a Raspberry Pi and PiHole for both DHCP and DNS.

Re: BT DNS Server Problems

WSH — Mon, 17 Nov 2025 20:00:22 GMT

This is one of the many reasons I've continued to use my Draytek as the gateway to my network after the switch to Digital Voice. My network gets its DNS settings from the Draytek not the SH2.

Re: BT DNS Server Problems

wuxmedia — Mon, 17 Nov 2025 21:19:00 GMT

Just use a Raspberry Pi and PiHole for both DHCP and DNS.

That would form part of the plan, but we come to the impasse that is the hub cannot change the DNS. Many years ago I did but the pi failed and a new hub was given to us.

I'll look for guides that serve my needs, and hopefully others, thanks all