Re: [Cerowrt-devel] [aqm] chrome web page benchmarker fixed

[Dave Taht <dave.taht@gmail.com>]

> The specific thing I've been concerned about was not the probability of
> a dns loss, although as you note the consequences are huge -
> but the frequency and cost of a cache miss and the resulting fill.
>
> This is a very simple namebench test against the alexa top 1000:
>
> http://snapon.lab.bufferbloat.net/~d/namebench/namebench_2014-03-20_1255.html
>
> This is a more comprehensive one taken against my own recent web history file.
>
> http://snapon.lab.bufferbloat.net/~d/namebench/namebench_2014-03-24_1541.html
>
> Both of these were taken against the default SQM system in cerowrt
> against a cable modem, so you can
> pretty safely assume the ~20ms (middle) knee in the curve is basically
> based on physical
> RTT to the nearest upstream DNS server.
>
> And it's a benchmark so I don't generally believe in the relative hit
> ratios vs a vs "normal traffic", but do think the baseline RTT, and
> the knees in the curves in the cost of a miss and file are relevant.

To be utterly clear here, the ~20ms knee in this data is a variable dependent
on the RTT to the nearest upstream DNS server. Most - nearly all -
ISPs - have a hefty dns server in their co-location facility, but the
baseline physical RTT is dependent on the actual technology in use.

The actual RTT of an query is dependent on the outstanding queue
length in a single queue AQM, unless otherwise prioritized. If prioritized
(cerowrt's 3 band system does this for queries coming from the router)
I imagine the packet loss rate drops hugely, also.

To give an extreme example of the DNS rtt problem, dns lookups over
satellite links take
800+ms, and this is one reason why web proxy servers are so common
in such environments as the whole query is shipped to a local-to-the-internet
proxy server so as to avoid this rtt cost. This technique is of increasingly
limited value in an age of e2e encryption.

Also: recently we've seen increasing use of non-local or otherwise redirected
dns servers such as here

http://www.cnet.com/news/google-confirms-turkey-is-blocking-its-dns-service/

It would be a good research project for someone to catagorize typical
nearest-upstream DNS RTTs, the availability of local-to-site dns
servers, hit/miss ratios
in homes and small business, the cost of dnssec, etc.


-- 
Dave Täht

NSFW: https://w2.eff.org/Censorship/Internet_censorship_bills/russell_0296_indecent.article