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<p class="MsoNormal"><span lang="EN-US">Count me in for second pony :D<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">Regards,<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">Grzegorz</span><span lang="EN-US"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:12.0pt;color:black">From: </span></b><span style="font-size:12.0pt;color:black">Petr Špaček <petr.spacek@nic.cz><br>
<b>Organization: </b>CZ.NIC<br>
<b>Date: </b>Wednesday 2019-07-10 at 09:14<br>
<b>To: </b>"ripe-atlas@ripe.net" <ripe-atlas@ripe.net><br>
<b>Subject: </b>Re: [atlas] DNS RTT over TCP: twice as long than UDP?<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On 09. 07. 19 13:51, Ponikierski, Grzegorz wrote:<o:p></o:p></p>
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<p class="MsoNormal">From this traffic looks like dig measures time between packets 4 (DNS<o:p></o:p></p>
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<p class="MsoNormal">query) and 6 (DNS response) which is precisely 8.5ms and matches what<o:p></o:p></p>
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<p class="MsoNormal">dig shows. Including TCP handshake it takes 23.7ms, 2.8x longer which is<o:p></o:p></p>
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<p class="MsoNormal">expected .<o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal">RTT can be measured on different layers for the same communication<o:p></o:p></p>
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<p class="MsoNormal">stream. In case of DNS over UDP we just ignores UDP overhead because it<o:p></o:p></p>
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<p class="MsoNormal">doesn't add any packets. With TCP additional packets are added which<o:p></o:p></p>
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<p class="MsoNormal">significantly increase time that end-user have to wait from first packet<o:p></o:p></p>
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<p class="MsoNormal">to get information that he/she needs. IMO RTT should always be measured<o:p></o:p></p>
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<p class="MsoNormal">from 1^st packet to packet which has information that you have actual<o:p></o:p></p>
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<p class="MsoNormal">data. If we want to measure raw DNS performance without overhead then it<o:p></o:p></p>
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<p class="MsoNormal">must be explicitly market it measurement description.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">If I could get a ponny, I would like to get both numbers:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">a) Time measured from moment of sending the very first packet (TCP SYN<o:p></o:p></p>
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<p class="MsoNormal">or UDP query) to arrival of DNS answer (not counting TCP FIN etc.).<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">b) Time measured from moment of sending the DNS query (also think of TCP<o:p></o:p></p>
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<p class="MsoNormal">fast open!) to arrival of DNS answer (not counting TCP FIN etc.).<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Having both numbers would allow to calculate latency of connection vs.<o:p></o:p></p>
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<p class="MsoNormal">DNS query separately, which gets even more important when we consider<o:p></o:p></p>
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<p class="MsoNormal">DNS-over-TLS etc.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">-- <o:p></o:p></p>
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<p class="MsoNormal">Petr Špaček @ CZ.NIC<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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