On Tuesday, September 25, 2007 09:36:23 AM +1000 Mark Andrews
The Introduction seems a bit defensive in stating that the DOS attacks
are not due to any flaw in the design of DNS or its implementations.
While the blame for the attacks lies with the attackers, some aspects
of nameserver configuration, behavior, and even protocol design make
the systems vulnerable to these attacks. I suggest that the defensive
language be removed.
No, the blame lies with the parties not implementing BCP 38.
A rogue end site should not be able to inject spoofed packets.
No; the blame for an attack _always_ lies with the attacker, not the
victim. While I certainly wish more network providers would implement BCP
38, those who fail to do so are not to blame for the bad acts of others.
FWIW, I believe the "defensive language" in question is neither necessary
nor particularly problematic, so I take no position on whether it should be
Finally, I wonder whether other more fundamental techniques for
addressing the problem have been explored. For instance, if DNS clients
were required to perform a simple handshake before a DNS server sent
a long response, fake requests would provide little amplification.
For example, requests that elicit long responses could prompt a
shift to TCP.
The DNS already does this. The DNS is optimised so that the
normal responses go via UDP and the exceptional responses via
It does, but normally only responses which are too long for UDP require the
use of TCP. A recursive nameserver could mitigate this type of attack by
lowering the maximum response size it is willing to send via UDP, forcing
the use of TCP and thus a three-way handshake for larger responses. The
tricky part is that setting the threshold too low can have serious
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