BT DNS Issues

[avicarage]

Is anyone else having issues with BT DNS this evening?

DNS shows as 81.139.56.100 as default but nothing will connect using this DNS. Manually changing my DNS to 8.8.8.8 (Google) instantly connects which would indicate an issue on BT's side as opposed to anything internal on my side. 

Tracert to 81.139.56.100 shows the below:

1 <1 ms <1 ms <1 ms 192.168.1.254
2 1 ms 1 ms 2 ms 172.16.18.217
3 * * * Request timed out.
4 10 ms 9 ms 9 ms 62.172.102.142
5 * * * Request timed out.
6 * * * Request timed out.
7 * * * Request timed out.
8 * * * Request timed out.
9 * * * Request timed out.
10 * * * Request timed out.
11 * * * Request timed out.
12 * * * Request timed out.
13 * * * Request timed out.
14 * * * Request timed out.
15 * * * Request timed out.
16 * * * Request timed out.
17 * * * Request timed out.
18 * * * Request timed out.
19 * * * Request timed out.
20 * * * Request timed out.
21 * * * Request timed out.
22 * * * Request timed out.
23 * * * Request timed out.
24 * * * Request timed out.
25 * * * Request timed out.
26 * * * Request timed out.
27 * * * Request timed out.
28 * * * Request timed out.
29 * * * Request timed out.
30 * * * Request timed out.

Trace complete.

[bobpullen]

I'm not sure that traceroute is indicative of anything. I see timeouts after few hops too: -

Bob> tracert 81.139.56.100

Tracing route to 81.139.56.100 over a maximum of 30 hops

  1    <1 ms    <1 ms    <1 ms  home.gateway [192.168.1.254]
  2    <1 ms     1 ms     1 ms  172.16.17.177
  3     *        *        *     Request timed out.
  4    10 ms     9 ms    10 ms  109.159.255.96
  5     7 ms     7 ms     7 ms  109.159.250.79
  6     *        *        *     Request timed out.
  7     *        *        *     Request timed out.
  8     *        *        *     Request timed out.
  9     *        *        *     Request timed out.
 10     *        *        *     Request timed out.
 11     *        *        *     Request timed out.
 12     *        *        *     Request timed out.
        ...

Yet the server is responding to DNS lookups: -

Bob> nslookup bbc.co.uk 81.139.56.100
Server:  UnKnown
Address:  81.139.56.100

Non-authoritative answer:
Name:    bbc.co.uk
Addresses:  2a04:4e42:400::81
          2a04:4e42:200::81
          2a04:4e42:600::81
          2a04:4e42::81
          151.101.0.81
          151.101.192.81
          151.101.128.81
          151.101.64.81

[avicarage]

Suppose it may be blocked from ping requests which would explain that to be fair.

Either way the BT DNS isn't allowing me to connect to the internet, whereas Google's public DNS is if I manually change it on any single device connected to either the WiFi or an ethernet connection, which would indicate that the issue lies on the BT infrastructure side as opposed to anything my side. I'll try to get back onto tech support this morning but was mostly wondering if it was a me issue or a wider one.

Cheers for the response!

[bobpullen]

And what does an  nslookup show from the command line similar to what I attempted? Assume it times out?

[Kimberlin]

@avicarage  If ISP's didn't lock their preferred DNS resolvers into their locked down routers, you could just change it at router level and be done with it. This is merely one reason I don't use a cheap mass produced ISP router so I can change the settings that ISP's would rather customers use.

[avicarage]

@bobpullen yes it does - I'd grab a screenshot but I am in the queue for tech support at the min (on Google DNS) and don't want to lose my spot 

[bobpullen]

@avicarage - very odd. The only other thing I can think is that your traffic is somehow not routing through the BT network (BT's resolvers will refuse lookups from non-BT sources I imagine).

Final thought is that there's something out on the network that thinks your IP address is 'bad' and treating lookups the same way. I wonder if you down your router for 30mins or so and then power it back up if you'll get a different IP address that doesn't exhibit the problem?

@Kimberlin - FWIW, the new SH3 does allow you to configure 3rd party DNS as part of the DHCP lease.

[Kimberlin]

@bobpullen  Wow! So BT have finally unlocked the DNS setting at router level on the SH3? Why on earth would they allow that? 😂

It doesn't make any difference to the likes of myself, I still wouldn't use it even if they sent me one. I'll stick with my own.

[avicarage]

@bobpullen well, my chat request has dropped out twice now so if it happens again I'll unplug modem + router whilst I head out for a few hours so I will be able to give that a go.

Last night it was working fine when I left the house around 1830 and was not working when I got back around 2130 - no power cuts, no power cycles, so it's really strange that it's just happened - I don't know anyone else using BT FTTP around here so can't check easily if it's a local thing but it's definitely a strange one.

As I only have the SH2, my fix (well, workaround) is going to be to just change the DNS across to google on all my devices. I'm half assuming that the suggested fix will be a factory reset of the router but we will see!

[avicarage]

So after leaving the router and modem powered off for an hour or so, we're back online with a new IP address and the BT DNS is now responding. 

Bit weird that it's happened without any sort of trigger (that I'm aware of) from my side.