You must add an IP Address to each Name Server under Configuration > Servers > Click on the name of the first name server and then choose IP Address, then type an IP address (192.168.0.101) and then add. Do the same for the second Name Server (192.168.0.102).
Then, in the SimpleDNS Server Service Properties look for the section called “Listening IP Address” , choose the IP Address that you assigned this server and then click the Add button. Do this for BOTH Name Servers and BOTH SimpleDNS Server Services.
These IP Addresses are used to tell SimpleDNS which IPs to allow zone transfers from…if they arent specified then SimpleDNS wont allow a zone transfer from your secondary name server like you want it to 🙂
(Also, just as a side note… I went into the SimpleDNS management interface directy, and went into the options and told it to only bind to port 53 on the specific IP Address that I chose above….that way it’s not listening for DNS on all IPs on the machine. This is probably more important in a single server installation, or where your DNS servers have multiple NICs or IPs.)