How common is lack of DNS server diversity?

Sat Jan 27 09:24:34 UTC 2001

> From: Sean Donelan [mailto:sean at donelan.com]
> Sent: Friday, January 26, 2001 7:01 PM
> 
> Mice and Men found that 38% of the .COM domains surveyed
> had all their name servers on the same subnet.  And 75%
> had one or more configuration errors.
> 
> http://www.menandmice.com/dnsplace/healthsurvey.html

Distribution requirements,of root name servers, is dependent on where in the
tree you live.

dot root servers should be spread out, as they are authoritative for
everything.
TLD root servers should also be spread out, they are authoritative for many
things.
SLD root servers need not be spread out so much, they are authoritative for
few things.
3LD root servers don't need to even leave their AS, if the AS is down the
servers, they are authoritive for, are probably also down.
4LD root servers ... who cares?

More interestingly, how many root servers allow recursive lookup?