large organization nameservers sending icmp packets to dns servers.

Tue Aug 7 18:19:45 UTC 2007

Hi Donald,

I'm not prepared to call it stupid, but you're right it can cause issues.

-J
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----- Original Message -----
From: Donald Stahl <don at calis.blacksun.org>
To: Jason J. W. Williams
Cc: Valdis.Kletnieks at vt.edu <Valdis.Kletnieks at vt.edu>; John Levine <johnl at iecc.com>; nanog at nanog.org <nanog at nanog.org>
Sent: Tue Aug 07 12:14:11 2007
Subject: RE: large organization nameservers sending icmp packets to dns servers.

> All things being equal (which they're usually not) you could use the ACK
> response time of the TCP handshake if they've got TCP DNS resolution
> available. Though again most don't for security reasons...
Then most are incredibly stupid.

Several anti DoS utilities force unknown hosts to initiate a query via 
TCP in order to be whitelisted. If the host can't perform a TCP query then 
they get blacklisted.

In addition, any UDP truncated response needs to be retried via TCP- 
blocking it would cause a variety of problems.

-Don

!SIG:46b8b686156533728213125!

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