I got a Main DNS (running on Unix) server with some A records to
Windows Nt Servers. Now i want to create a failover for 1 of this a
records. For exampe:

ip Server 1= 10.0.0.1
ip Server 2 =10.0.0.2

normaly when pinging the a record, i get back the ip from Server 1
(10.0.0.1). But now i want, that when Server 1 is down, the main dns
server will automatic return the ip of server 2 (10.0.0.2)

Is this posible? And if it is, How can i do it?