Re: [DNSOP] Enough latency obsession Re: Review of draft-ietf-dnsop-cookies-00

"Guangqing Deng" <> Mon, 29 December 2014 06:52 UTC

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Date: Mon, 29 Dec 2014 14:52:14 +0800
From: "Guangqing Deng" <>
To: "Mukund Sivaraman" <>, "Nicholas Weaver" <>
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Subject: Re: [DNSOP] Enough latency obsession Re: Review of draft-ietf-dnsop-cookies-00
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 Totally agree. At least there are almost no people complaining of the DNS resolution being too fast, but there do exist some ones who think the DNS resolution delay is not as short as they expected, especially those running applications depending on the DNS resolution.

Guangqing Deng
From: Mukund Sivaraman
Date: 2014-12-17 09:21
To: Nicholas Weaver
CC: dnsop; Paul Vixie
Subject: Re: [DNSOP] Enough latency obsession Re: Review of draft-ietf-dnsop-cookies-00
Hi Nicholas
On Tue, Dec 16, 2014 at 02:44:40PM -0500, Nicholas Weaver wrote:
> Its time to stop obsessing over latency in DNS!
> DNS doesn't exist in a vacuum, but then goes to at minimum, a TCP
> handshake, and who knows what else beyond it.  Amdahl's law matters.
> How many headaches would go away if all DNS is over TCP?  And how much
> would it really make a difference in Latency?
Surely a lot of problems would go away. But I don't think we can say
that latency doesn't matter. Though it is 2 roundtrips instead of 1, the
wait effectively doubles, and may increase further by a ~constant factor
during recursion. This would be conspicuous on long networks.
As DNS resolution is at the head of the batch of items that is done when
a user uses a network service, it adds to the average turnaround time of
every item on the list.
TCP performance "feels" different depending on what it is used for. On
LFNs, slow-start can throttle up fast (being a doubling throttle), and
due to the receive window TCP can deliver a lot of data quickly
vs. DNS-like UDP that restricts flow to request/response pairs.
For DNS, where there isn't a lot of data to transmit (in normal
queries), TCP connection setup is a big part of overall time to service
a request and it may not amortize well.
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