DNS Resolution Slow

[#1]

This is why I say PN's cached dns is slow.
212.159.6.9 is consistently the slowest in that group of public dns resolvers. The other PN resolver is not much better.
PN have the home advantage, so IMO their cached speed should be one of the best.
Having said that, I very much doubt DNS has anything to do with your perceived speed issues.

[#2]

Err... Pretty colours!
So, just to summarize where we're up to:
1. Moving from Be* to PlusNet, one can expect DNS RTT to approximately double for cached queries, regardless, for practical purposes, of what server is used.
2. Nobody knows why but it is something to do with latency in PlusNet's network.
3. This has an effect in that web browsing is slower.
4. That effect is not really noticeable on fast hardware, but is noticeable on older PCs for obvious reasons.
5. It remains to be seen whether the latency is inherent in the ADSL setup or in the wider network.
6. I shall report back when the connection is all fibre and ADSL is therefore no longer a factor.

[#3]

Did you tweak the MTU/RWIN on the older machine (running Win XP?) for Be, which now might need changing due to a different MTU and increased latency?

[#4]

No. All default. And MTU is now standard 1500 on 21CN, as on Be*.
I think the reason for the slow browsing experience isn't in much doubt.
The reason for the comparative sluggishness of DNS traffic on PlusNet's network, however, is not at all clear to me. It doesn't seem to be clear to PlusNet either - or if it is, they aren't saying. Maybe, as you suggested, latency is simply higher overall, for whatever reason.
Can we be sure that outgoing DNS requests are being properly prioritised at ingress to the DiffServ domain?

[#5]

Quote from: SuperZoom

I think the reason for the slow browsing experience isn't in much doubt.

What is it?

[#6]

Hi Kelly, thanks for coming in. It's a great opportunity to keep this thread on track with some input from PlusNet. So in order to maintain the focus, I'm going to re-post my original question and edit it slightly to remove the justification for asking. That way we can focus on the question and not the reason for it. We can treat it as technical curiosity instead.

Quote from: SuperZoom

Having moved from Be*, I am finding DNS resolution times to be a lot slower on PlusNet. Specifically, using the ISP's own DNS servers (as assigned to the router) takes over 80% longer on average, and using OpenDNS servers takes over 90% longer on average. It seems to be something to do with the way the network is set up rather than the servers themselves. As far as I can tell there is nothing wrong with PlusNet's DNS servers and the same kind of delay is present when using public servers eg. Google or OpenDNS. All my hardware has remained the same (including the router,) so the only change is PlusNet network vs Be* network. Can anyone explain this? Could it be the traffic management system? How is DNS traffic prioritised? Or interleaving on the ADSL upstream? (Be* doesn't error-correct the upstream). I'm at a loss and tech support just keep saying there is no problem with the servers (I agree: there isn't). [...] Thanks for any insights or suggestions.

Do you have any comment on this at all?  -->

Quote from: SuperZoom

Can we be sure that outgoing DNS requests are being properly prioritised at ingress to the DiffServ domain?

Thanks for any and all insights.

[#7]

Boiling back to the question then.
How do you know it is slow?
What speeds for resolution were you seeing on your BE connection on internal and external look ups vs our connections.
(More I could say/ask, but lets get this bit clear first )

[#8]

Thanks.
There has been some improvement, in fact: which is perhaps what you're driving at?
Focusing only on the numbers and not the perceived effects, which we are now putting to one side in the name of pure technical curiosity, the same methodology as previously used repeated just now returns an average of 26.71ms for the PlusNet servers (OpenDNS takes longer, though, as before).
So what's changed your end?
Any comment on the traffic prioritisation side of things?

[#9]

I don't think we've changed anything. 
Re prioritisation, there isn't any upstream, downstream DNS traffic is prioritised.

[#10]

Quote from: SuperZoom

Well, using cURL just now, I get this: URL Fetched:            http://www.bbc.co.uk/news/ Name resolved after:    0.070 Secs Connected after:        0.100 Secs Transfer started after: 0.150 Secs Total transfer size:    118676 Bytes Total time taken:       4.016 Secs Perceived Speed:        29550.000 Bytes/Sec URL Fetched:            http://www.telegraph.co.uk Name resolved after:    0.070 Secs Connected after:        0.100 Secs Transfer started after: 0.140 Secs Total transfer size:    202659 Bytes Total time taken:       5.107 Secs Perceived Speed:        39682.000 Bytes/Sec

Taking 4 or 5 seconds to transfer 100KB or 200KB cannot possibly be explained by the DNS servers taking 70ms. There must be some other reason, unrelated to ping or DNS response times. Or there is something wrong with those numbers from cURL.

[#11]

So, focusing on the DNS, there appears to have been an approximately 20% improvement in name resolution times from here using PlusNet's servers over the last couple of days.
Where has that improvement come from?
Is it just DLM doing its thing with the interleaving?
It might actually be the best I can hope for since ping to 212.159.6.9 averages about 24ms.

[#12]

SuperZoom.  Could you do a speedtest on http://www.speedtest.btwholesale.com/ and let us know the results and what your bt speed profile is.

[#13]

Since Latency and DNS response times have been mentioned I have a good illustration of relationship as my line has had a couple or so resyncs with interleaving added then removed from upstream, attached are latency and DNS response graphs for the last week.

[#14]

Sure.
Download 5.75Mbps with an IP Profile of 5.93; Upload 0.77Mbps with a profile of 0.83. Ping latency reported as 40ms.
Current sync speed is 6720Kbps down (Attenuation 44db and Noise Margin 6db) and 896Kbps up (Attenuation 13db and Noise Margin 10db).
This machine is connected via a Linksys gigabit ethernet card to a Cisco gigabit switch and from there to the router. Everything else was shut down for the test and the router and browser were both restarted, as per the instructions. It's a very old machine, which is why the cURL results appear so slow, and why DNS performance makes such a difference (although I'm sure you realise the limitations of using a tool like cURL for absolute as opposed to comparative benchmarking of such things).
I'm glad that DNS performance seems to have improved somewhat. However, name resolution times were indisputably shorter when I was connected via the Be* network and it would be interesting to know why, and even more interesting if they could be brought down to that level (around 18ms) on PlusNet. That would be great for everyone if it were possible.

[#15]

Thanks, W23 - those are very interesting graphs.