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Re: DNS deluge for

  • From: Jon Lewis
  • Date: Sun Feb 26 11:54:11 2006

On Sat, 25 Feb 2006, Rob Thomas wrote:

As many say, you own your network, and are free to run it as you see
fit.  :)  That said, please be aware that if you leave your name
servers open to recursive query requests from any source, you WILL
unwittingly help to amplify these attacks.  It's the same as ICMP
directed broadcast and the like.
This has been an issue for years. Before the DDoSers started using open recursive DNS servers as a modern way to "smurf", spammers were abusing them by registering a domain, setting up DNS, loading the data into open recursive servers (by sending them queries), and then pointing the domains at those recursive servers...getting free DNS service and misdirecting complaints.

The argument that DNS servers have always been open to recursion (so we shouldn't change it) sounds a lot like the open SMTP relay issue 5-10 years ago. It took years, but all but a few wingnuts seem to have finally caught on to the idea that open SMTP relays are a bad idea...enough so that spammers had to move on and adapt to open proxies, and then to botted systems / trojan proxies.

Besides, don't the DNS specs dictate that a proper DNS resolver will try again with TCP if the server tells it the UDP reply was truncated?

Jon Lewis | I route
Senior Network Engineer | therefore you are
Atlantic Net |
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