HSRP-like virtual DNS services.

[Jonathan de Boyne Pollard]

BM> [DNS Client libraries] typically allow you to specify multiple 
nameservers,
BM> but they often have a relatively long timeout (a few seconds) to switch
BM> over to the backup server.  And they go through this timeout for
BM> every query; [...]

Not all DNS Client libraries do that.  There is one particular DNS 
Client library that, due to an implementation bug (since fixed, but with 
the erroneous version still in widespread use), queries the alternate 
proxy DNS server first for every subsequent query after it has once 
timed out trying to query the preferred proxy DNS server.