The better solution is to configure the local Bind of Zeroshell to use the DNS of your ISP as forwarder. Use the section [DNS]->[Forwarders] of the web interface and add the DNS of the ISP with domain ANY. In this manner, Zeroshell won’t use the ROOT DNS, but wil directly contact the DNS you specify. The advantage of this configuration is that the local Bind acts as local DNS cache.
Regards
Fulvio