Most of our DSL customers have modem/routers that resolve DNS externally. And most of those have no configuration option to stop it. So, we took the unfortunate step of ACL blocking DNS requests to & from the DSL network unless the requests are to our DNS servers. Suboptimal, but it stopped the DNS amplification attacks. -----Original Message----- From: Mikael Abrahamsson [mailto:swmike@swm.pp.se] Sent: Monday, April 01, 2013 11:51 AM To: Chris Boyd Cc: nanog@nanog.org Subject: Re: Open Resolver Problems On Mon, 1 Apr 2013, Chris Boyd wrote:
Just back to the office, and started checking my networks. Found one of the resolvers is a Netgear SOHO NAT box. EoL'd, no new firmware available. Anyone have any feeling for what percentage are these types of boxes?
If you buy "type of box" mean "small SOHO NAT router which does DNS resolving on the WAN interface" then I'd say "a lot". Someone does a rollout of new software and configuration and happens to mess up the config file (or the vendor just happens to enable global dns resolving in the new software) and this slips through testing, then you're there. I believe this happens all the time. That's why the publication of these lists are important, in a lot of cases there are a lot of people who are simply not aware of these devices doing this, and they need to be poked to notice. -- Mikael Abrahamsson email: swmike@swm.pp.se