From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-we0-x232.google.com (mail-we0-x232.google.com [IPv6:2a00:1450:400c:c03::232]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id DB9FA21F25A; Fri, 18 Apr 2014 12:40:54 -0700 (PDT) Received: by mail-we0-f178.google.com with SMTP id u56so1892906wes.9 for ; Fri, 18 Apr 2014 12:40:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; bh=huRzyduJCbGVE4GprxWO/SHWpDnlLoBcWpnJdcecSK4=; b=a++5dt9tZvjJoBn81IANKuIfc3hL198GkJY7c6/lYmc6f+sac2S8Sr6Xanp9WGxW9l GISk5mVsEqVorM60mzT6o/b+5aatXeZot4F9C50bKSH8NUy74nHR3DoDNJaqnCEfOJP7 raO0rU58dy7CnuXq1ZmLRmNtDhVUlEuLz2/cmslM9zS5jB26Sfnj1gG+P/a4SrUvgb+5 09GB9YJDGSppFU8Hg7obk2eQeHomyniPetJRNnmk1Tpo7Iz6P1dzmp5LE3LNkwBNRoKR CO9b5mKQFIj65xnR8Gamz1Cd2spT6+ompXvyKcTSCY0ZODbn82pstVBVRw9BI94ERhyH Qf6A== MIME-Version: 1.0 X-Received: by 10.180.76.166 with SMTP id l6mr3596182wiw.17.1397850052958; Fri, 18 Apr 2014 12:40:52 -0700 (PDT) Received: by 10.216.177.10 with HTTP; Fri, 18 Apr 2014 12:40:52 -0700 (PDT) In-Reply-To: References: Date: Fri, 18 Apr 2014 12:40:52 -0700 Message-ID: From: Dave Taht To: Greg White Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Cc: =?UTF-8?B?V2lsbGlhbSBDaGFuICjpmYjmmbrmmIwp?= , "aqm@ietf.org" , "cerowrt-devel@lists.bufferbloat.net" , bloat Subject: Re: [Cerowrt-devel] [aqm] chrome web page benchmarker fixed X-BeenThere: cerowrt-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: Development issues regarding the cerowrt test router project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 18 Apr 2014 19:40:55 -0000 > 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 depende= nt 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-intern= et proxy server so as to avoid this rtt cost. This technique is of increasingl= y limited value in an age of e2e encryption. Also: recently we've seen increasing use of non-local or otherwise redirect= ed 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. --=20 Dave T=C3=A4ht NSFW: https://w2.eff.org/Censorship/Internet_censorship_bills/russell_0296_= indecent.article