Internal hosts DNS problem

[Jamie Mcparland]

Internal hosts DNS problem. 

Our DNS is hosted outside our network by our ISP. The DNS records point
to a webserver behind our firewall. Our firewall has a external nic with
an IP for the firewall and aliases for all the other static Ips we have 

IE
Firewall is eth0 with an IP of 198.236.226.12
Firewall ethO:1 accepts connections for 198.236.226.31 and redirects all
that traffic to 172.16.16.31

So from the outside world everything works fine. On our private network
we set up a DNS server for our local clients. 

We set up our internal DNS server to forward all requests to our ISP. 
But for our internal webservers we set up a record with the private
addresses of the webserver to resolve to. 

IE a PC internally trying to access our webserver will query our
internal DNS server and resolve to 172.16.16.31 and NOT 198.236.226.31 

Usually this works great. But sometimes it doesn't. You see as far as
the Root servers on the internet are concerned our ISP is the SOA not
us. So sometimes when our clients query our internal DNS they end up
getting the forwarded DNS entry from our ISP and resolve to
198.236.226.31 and not 172.16.16.31

Have any ideas on how to correct this problem? Sorry if this sounds
messed up.. I don't know who else to explain it. - Jamie

Here's a copy of my internal dns zone file. 
########################################
$ttl 38400
newberg.k12.or.us.    IN    SOA    listserv.newberg.k12.or.us.
jamie.listserv.newberg.k12.or.us. (
            993772534
            800
            3600
            432000
            38400 )
newberg.k12.or.us.    IN    NS    listserv.newberg.k12.or.us.
listserv.newberg.k12.or.us.    IN    A    172.16.16.36
mail.    IN    MX    1 newberg.k12.or.us
www.newberg.k12.or.us.    IN    A    172.16.16.32
########################################

And heres a copy of my named.conf

options {
    directory "/etc";
    pid-file "/var/run/named.pid";
    forwarders {
        198.236.20.8;
        };
    forward first;
    };

zone "." {
    type hint;
    file "/etc/db.cache";
    };

server 198.236.20.8 {
    transfers 5000;
    };

zone "newberg.k12.or.us" {
    type master;
    file "/etc/newberg.k12.or.us.hosts";
    };

zone "myzone" {
    type forward;
    forwarders {
        198.236.20.8;
        };
    };

logging {
    channel test {
        file "/var/log/test";
        severity info;
        };
    category load {
        null;
        };
    category statistics {
        null;
        };
    category security {
        null;
        };
    category queries {
        null;
        };
    category config {
        null;
        };
    category db {
        null;
        };
    category response-checks {
        null;
        };
    };