Configuring RNDC to work through Firewalls

[Vincent K. Britton]

I have my DNS Servers on separate Subnet's at isolated locations.  Both
are behind firewalls.

 

I am trying to configure the firewalls to allow RNDC traffic through.

 

When I try to perform an RNDC -s remote.server.ip.address reload I get
rndc: connect: unexpected error

 

Can anyone point me to a HowTo for this?  Has anyone done this already?
What ports or ranges need to be allowed?