Poor DNS response on FFB

[Philh56]

I have recently upgraded to FFB. The new router has the following DNS set;

Primary 90.207.238.97

Secondary 90.207.238.99

The performance of these is very poor. Individual DNS lookups (and therefore web page loads) take 2-3 seconds. I have set my local device DNS settings to 8.8.8.8 and performance is excellent.

I believe there is no way of changing the routers default DNS settings ? That being so; is there any way to raise this as a service issue with Sky ?

[JimM1]

@Philh56 Yes give them a call, dial 150 from your landline, you also may wish to take a look at the link below! From @-rpnz- 

Answered: Re: Dsl username & password | Sky Community

[-rpnz-]

Hi @Philh56 

At an aggregate level we typically see >95% of all DNS queries answered within 10ms, anything outside of this would be flagged as an issue.

If your DNS queries are consistantly taking longer than that, there may be a more isolated issue.  Are you able to isolate just the DNS query response time from the overal webpage load, by for example using browser developer tools, or just monitoring DNS queries specifically?

[Philh56]

I think the problem is related to the hub, rather than the DNS server.

Heres what I see.

When setting the Windows 10 IP4 adapter to pick up the DNS settings via DHCP (the default in Windows 10) the IP address of the DNS is set to the IP address of the router (i.e. 192.168....). I presume the router is doing some DNS caching so is broadcasting itself as the DNS resolver. This gives me a page response time of about 2-3 seconds per URL resolution. I'm timing this on a browser based on getting back the first HTML 

When I set the Windows 10 adapter directly to 8.8.8.8 or to 90.207.238.99 (the Sky Router DNS server) the response time is then normal.

I have repeated this configuration change multiple times, on more than one device; and get consistent results - swapping from dynamic DNS allocation to Fixed (with a DNS flush in between) irrespective of whether Sky or Google DNS server, removes the page fetch stall.

I also find that once I've reconfigured Windows 10 Network Adapter settings from Dynamic DNS assignment to fixed, then back again, the problem 'seems to go away'. 

I'll keep looking to see if I can find a better pattern or other consistent behaviour. 

[-rpnz-]

Hi @Philh56 

Thanks for coming back with your diagnostic steps and results.

What model Sky Hub do you have?

If you're open to more testing, is IPv6 still enabled on your Sky Hub (it should be by default), and then check to see if your Windows clients are learning and installing the Sky Hub's IPv6 address as DNS servers.   Then, I'd check (with something like nslookup / dig / etc.) to see if there's any difference beterrn resolving DNS over IPv4 and then IPv6.

Then I'd use Wireshark to take packet captures to see what's actually going on with the DNS queries, they should generally always be answered and never time out, even if the answer is an error.    If you see an error, then we can investigate that, but given the delay in timing, it's more likely we won't see an error but instead a timeout, which then would lead us to check connectivity between the client and the DNS proxy.    If you can prove connectivity isn't an issue, then it's possible there's an issue with the DNS proxy inside the Sky Hub itself, but we'd need to escalate that to other teams to investigate.

[Philh56]

Hi,

This morning I am back to >5 second DNS resolution (measured using DevTools on Edge).

Using ipconfig /flushdns restores performance to the expected level. Suggestive of a Windows issue; but the problem only occured when the new router was installed; and Win10 + Win11 DNS caching isn't normally a problem.

I will check the IPv6 as you suggest.

[Philh56]

Hi,

My router is model SR203. Yes Ipv6 is enabled on the router. My IPv4 and IPv6 Windows adapter settings are both set to DHCP for obtaining the DNS address automatically.

[Philh56]

The only difference I see with Ipv4 vs IPv6 DNS resolution is;

When I run nslookup bbc.co.uk 192.168.... to force IPv4 resolution the server name is shown as "SkyRouter.Home"
When I run nslookup bbc.co.uk fd1c:a20:e5ae.... to force IPv6 resolution the server name is shown as "UnKnown" 

I dont know whether that is significant.

[-rpnz-]

---

@Philh56 wrote:

The only difference I see with Ipv4 vs IPv6 DNS resolution is;

When I run nslookup bbc.co.uk 192.168.... to force IPv4 resolution the server name is shown as "SkyRouter.Home"
When I run nslookup bbc.co.uk fd1c:a20:e5ae.... to force IPv6 resolution the server name is shown as "UnKnown" 

I dont know whether that is significant.

---

That's because there's no local reverse DNS (PTR record) for the Sky Hub's IPv6 ULA address, but there is for the IPv4; it shouldn't impact query resolution.

Are they both replying to your manual queries without delay?

So next up I'd suggest taking a packet capture and just watching what Windows does.  Where is Windows sending queries to?  Does it get responses or do they time out?     It's obviously getting replies at some point otherwise nothing would work, so in the packet capture, see if we can spot any difference with the queries that are timing out (presumably).