[dns-operations] Force TCP for external quereis to Open Resolvers?

Jim Reid jim at rfc1035.com
Sun Mar 31 12:32:13 UTC 2013

On 31 Mar 2013, at 10:30, Xun Fan <xunfan at isi.edu> wrote:

> So do you think "force TCP for external queries to OR" is a feasible
> solution to DNS reflect amplification problem?

It's a nice idea that's worth trying.

I'm not sure it will make a difference though. The bad guys won't bother to do TCP for the obvious reason and will stick with their current, DNS protocol conformant, behaviour.

Remember too that in these DDoS attacks truncated UDP responses would still be going to spoofed addresses. So those victims still get hit, albeit without the amplification factor of a chubby DNS response.

I expect TCP to an anycast resolver -- say -- will prove tricky for long-lived connections.

Keeping state for bazillions of DNS TCP connections to a resolving server will present further challenges. [Maybe TCPCT could help.] That could lead to a new DoS attack vector: overwhelming a resolving server with too much TCP traffic. Though that could be done already I suppose.

Another problem is lots of crapware -- CPE, hotel networks, coffee shop wi-fi, etc -- assume DNS is only ever done over UDP. Anyone stuck behind that already loses whenever they get a truncated response. They'll have much bigger problems if resolving servers default to truncation and TCP retries for everything. I suppose more use of DNS over TCP could provide an incentive to get those broken middleboxes fixed. Wouldn't hold my breath though....

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