Is it Bad Practice to Use NS Server that is Usually Turned Off?

[s.fenster at gmail.com]

Hi,

I want to know if it is considered bad practice to use a name server
that is usually not responding.  My goal is to quickly be able to
change name servers in the case of a disaster at the main site.

Our setup is the following:

ISP hosts our zone file, which looks like this:

myserver    IN NS wan1.domain.com
                 IN NS wan2.domain.com

wan1.domain.com    IN A   1.2.3.4
wan2.domain.com    IN A   2.3.4.5

I control wan1.domain.com and have A records for my servers.  In order
to prevent requests from going to wan2 (which is our backup site), I
would disable access to that dns server.  As I understand it, there is
no priority for NS records like there is for MX records.  I understand
this might create more traffic on 2.3.4.5, but it may be an acceptable
consequence.

My question is, will my users see a delay when resolving
myserver.domain.com? I saw that BIND uses a relatively smart (as
compared to round robin) algorithm to determine which name server to
query.  I assume my ISP is using BIND (but I am not sure).

The alternative is to use a managed DNS service that detects down
links and switches NS servers.  It would be great if my ISP did this,
but I suspect they don't.  And I don't want to wait for them to change
my zone file and wait for it to propagate.  I also don't want to give
my DNS over to a managed provider - I like to be in control of my DNS.

So if is bad to do what I propose, which is to have an NS record point
to a server that is usually off, I would probably just leave it as is,
and just update my zone file with the ISP if needed.

Thanks,

Seth