Outbound Requests

•	Outbound DNS Requests

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Send outbound DNS and zone transfer requests via
Specify which IP versions (IPv4/IPv6) and from which local IP addresses outbound requests should be sent.
It can be useful to select a specific local IP address for secondary DNS servers with multiple IP addresses (multi-homed) if the primary DNS server only allows zone transfers from a specific IP address.
When both IPv4 and IPv6 are enabled, you can also enabled "Prefer IPv6 servers" to have the server attempt to resolve DNS over IPv6 whenever possible.

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Send outbound DNS requests from port number
Specify if Simple DNS Plus should use a new random port number for each outbound request, or send all outbound requests from the same port number.
Using random port numbers helps protect against DNS spoofing attacks. For details see How to secure you server / DNS spoofing.
Using a fixed port number is not recommend unless the DNS server is not offering recursion or it is forwarding to another secure DNS server for all domains.