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

[Paul Vixie]

> >> 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 dependant on the routing advertisement needing to be withdrawn if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.

this is an argument for multiple NS RRs and/or multiple A RRs per NS,
with each A RR being a distinct anycast cloud (or a distinct stripe of
a non-fate-sharing anycast cloud, as in UltraDNS's case).  it is not,
in and of itself, an argument for mixed anycast/unicast nameservers.