[98364] in North American Network Operators' Group
Re: large organization nameservers sending icmp packets to dns servers.
daemon@ATHENA.MIT.EDU (Leigh Porter)
Mon Aug 6 12:35:23 2007
Date: Mon, 06 Aug 2007 17:13:51 +0100
From: Leigh Porter <leigh.porter@ukbroadband.com>
To: Valdis.Kletnieks@vt.edu
CC: Drew Weaver <drew.weaver@thenap.com>,
"'nanog@merit.edu'" <nanog@merit.edu>
In-Reply-To: <29395.1186415828@turing-police.cc.vt.edu>
Errors-To: owner-nanog@merit.edu
But why would they care where the nameserver is? Point 2 would seem to
be a little stupid a thing to assume. Also, what happens if, at that
moment, the ICMP packet is stuck in a queue for a few ms making the
shortest route longer.
--
Leigh
Valdis.Kletnieks@vt.edu wrote:
> On Mon, 06 Aug 2007 11:53:15 EDT, Drew Weaver said:
>
>> Is it a fairly normal practice for large companies such as Yahoo! And
>> Mozilla to send icmp/ping packets to DNS servers? If so, why?
>>
>
> Sounds like one of the global-scale load balancers - when you do a (presumably)
> recursive DNS lookup of one of their hosts, they'll ping the nameserver from
> several locations and see which one gets an answer the fastest.
>
> Yes, it's a semi-borkken strategy, because it assumes that:
>
> 1) ICMP is handled at the same rate as TCP/UDP packets in all the routers
> involved (so there's no danger of declaring a path "slow" when it really isn't,
> just becase a router slow-pathed ICMP).
>
> 2) That the actual requester of service is reasonably near net-wise to the
> server handling the end-user's recursive DNS lookup.
>
