How to setup a backup NameServer?

[Niall O'Reilly]

At Tue, 29 Apr 2014 10:24:58 +0000,
houguanghua wrote:
> 
> Yes, I had asked the same question months ago. 
> I'm designing how to protect DNS for an ISP. The zones are not owned
> by the ISP. The ISP wants to proect the DNS query during attacking.
> So it's not standard DNS solution. During the attacking, the backup
> server will provide the DNS query and it works even if it can't
> refresh zones from primary NS.

  Which (or how many) zones do you expect your backup server to work
  for?

  /Niall