[dns-operations] First experiments with DNS dampening to fight amplification attacks

Paul Vixie paul at redbarn.org
Mon Oct 1 16:30:17 UTC 2012

On 2012-10-01 4:00 PM, John Kristoff wrote:
>> ...
>> We could encode the encrypt the correct destination in the CNAME, for
>> A and AAAA this is trivial. If you come back to resolve
>> encoded-, you get etc. For
>> extra resilience encrypt it.
>> I did not think this through too deeply, but what do people think?

as before, i think this could be done for a recursive talking to a stub,
but that an authority server should only speak zone truth. since the
stub/recursive relationship can be kept spoof-free using ACL's and
network perimeters, what we primarily need is solutions in the
recursive/authority relationship. and i would not be comfortable seeing
synthetic CNAME's added to those transactions.


> Why would this, or other similar proposals, be more preferable than
> just sending back truncated packets to signal for TCP?
> This latter approach has been widely used in network gear over the
> years with a fair amount of success, and now thanks to Paul and Vern's
> work, seems to be a promising feature in the application itself.

noting that other network equipment has been doing this, i want to make
sure everyone knows the distinction of DNS RRL's approach: packet
attenuation. we only insert TC=1 "slip frames" periodically, not on a
1:1 basis with potentially fake queries. slip frames are the same size
as queries, so there is no bit-level amplification. and the packet level
replication is attenuated. this makes a DNS RRL server "less attractive"
than a directed attack, which is literally the best we can hope to
accomplish here -- the attacks will go on but our authority servers
don't have to be involved.


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