[98370] in North American Network Operators' Group
Re: large organization nameservers sending icmp packets to dns
daemon@ATHENA.MIT.EDU (John L)
Mon Aug 6 14:04:30 2007
Date: Mon, 6 Aug 2007 13:47:37 -0400 (EDT)
From: John L <johnl@iecc.com>
To: Valdis.Kletnieks@vt.edu
cc: nanog@nanog.org
In-Reply-To: <4122.1186421692@turing-police.cc.vt.edu>
Errors-To: owner-nanog@merit.edu
>> Why would they ping rather than just sending the query to all of the
>> NS and see which one answers first? It's an IP round trip either way.
>
> If you have sites in San Fran, London, and Tokyo, and you launch a ping from
> all 3 and see which one gets there first, you'll *know* the RTT from each site.
>
> If you just send DNS replies from all 3, you don't have a good way of telling
> which one got to the destination first.
Um, unless I seriously misunderstand the client DNS cache wants to know
which server is closest. So it sends DNS queries to all three NS at the
same time. Then it waits for the answers. Whichever one answers first is
the closest. What am I missing?
Regards,
John Levine, johnl@iecc.com, Primary Perpetrator of "The Internet for Dummies",
Information Superhighwayman wanna-be, http://www.johnlevine.com, ex-Mayor
"More Wiener schnitzel, please", said Tom, revealingly.
