[dns-operations] Too Open (Was: OpenDNS makes your Internet work better

Florian Weimer fw at deneb.enyo.de
Wed Jul 19 05:49:11 UTC 2006

* John Payne:

> On Jul 14, 2006, at 1:20 PM, Brad Knowles wrote:
>> Not true.  By having a mix of anycast and unicast service  
>> addresses, at least those unicast service sites don't have the  
>> problem of being dependant on the routing advertisement needing to  
>> be withdrawn if the pod should go down.
> What happens to the packets for the down unicast server?

They cease to be sent. 8-) AFAIK, most DNS resolvers keep track which
servers are down (or are lame) and query them only occasionally, to
see if the problem still persists.  Some of them even store the RTT.

You can't do such optimizations at the application level if all name
servers are hidden behind very few anycast addresses.

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