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Re: DNS deluge for x.p.ctrc.cc
From: bmanning () vacation karoshi com
Date: Sat, 25 Feb 2006 08:41:01 +0000


] other cctld servers have seen what are effectively ddos.  rob thomas
] seems to have the most clue on this, so i hope this troll will entice
] him to speak.

Did someone say "troll?"  :)

Yes, this is a real problem.  These attacks have exceeded several
gigabits per second in size, and during one attack 122K DNS name
servers were abused as amplifiers.  Ouch!

This abuse can be mitigated.  Here are a few tips.

        <there has -GOT- to be a better name for this>

Limit recursion to trusted netblocks and customers.  Do not permit
your name servers to provide recursion for the world.  If you do,
you will contribute to one of these attacks.

        <recursion is a fundamental DNS design feature,
         restricting it to "walled gardens" cripples its usefullness>

Watch for queries to your name servers that ask for "ANY" related
to a DNS RR outside of the zones for which you are authoritative.
This DNS RR will be LARGE.

        <a valid concern, w/ the following caveat:  LARGE, relative
         to current traffic>

Limit UDP queries to 512 bytes.  This greatly decreases the
amplification affect, though it doesn't stop it.

        <limiting UDP to 512 has other, unwanted effects,
         edns0 for one... crippling ENUM, DNSSEC, IPv6, etc...
         is this really what is wanted?>

Scan your IP space for name servers that permit recursive queries.
It's amazing just how many of these name servers exist.

        <yup... again, a feature that has made the DNS as useful as
        it has become>

Refer to the following guides for some excellent insight and
suggestions.

   <http://www.us-cert.gov/reading_room/DNS-recursion121605.pdf>
   <http://cc.uoregon.edu/cnews/winter2006/recursive.htm>
   <http://dns.measurement-factory.com/surveys/sum1.html>

Note we have our own Secure BIND Template which will help on the
BIND side of life.

   <http://www.cymru.com/Documents/secure-bind-template.html>

If you need assistance with any of this, have endured one of these
attacks, or have any other questions, please don't hesitate to ping
on us at team-cymru () cymru com   We're here to assist!

Thanks!
Rob.
-- 
Rob Thomas
Team Cymru
http://www.cymru.com/
ASSERT(coffee != empty);

        ok, so i'm being a bit of a curmudgion here but just how,
        if we throttle DNS to the minimum suite for todays services,
        can we be expected to add new features/services?   grump grump grump...

-- (grumpy) bill


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