than again all depends on what you want to do.
you could have, for example 2 DA servers,
set up already, and maybe not much on them.
suppose your main domain, blah.com is on
server A. you could take an IP address
from server A, and take one from server B.
go to your registrar and register these as
ns1.blah.com and ns2.blah.com.
edit blah.com zone file on server A to use
these nameservers. set up multi-server on
server A to push to server B.
you could use server B for assorted reseller
sites, or assorted user sites, handling all of
the dns for that independently on server B
ignoring everything else, with maybe
nameservers for the reseller, or for you own
private reseller account you set up on it,
doesn't matter, you're free to fiddle around.
Then, what if you want to add more servers....
on each new server, at set up, change
admin settings to use ns{1,2}.blah.com
and you could set the hostname as
boxX.blah.com (x = 1,2,3....) depending
on which server. set up every new box
with multi server to push to server A and
server B. every new account you add
on these new servers would use
ns{1,2}.blah.com as nameservers, and
the zone files all get pushed to server A
and server B as you want.
you could end up with, say, 10
'additional' servers. all domains on them
now set up to use ns{1,2}, and any
new or edited zone files being pushed to
server A and server B. Only
these servers will be answering to dns
queries as they're the only ones you've
set up at your registrar.
no more having to have ns{1,2} on server1,
then ns{3,4} on server 2, and ns{5,.6}
on server 3, etc......
you don't even need to have any domains
on your first 2 DA servers, get 2o low
price ones, and you now have
2 servers devoted to dns. nice.