Network layout: Multi-homed computers
The computers from both public side and provate side register DNS records into one DNS server. For example, E-mail server:exch1 will have two A records registered.
Exch1 Host (A) 24.120.80.80
Exch1 Host (A) 192.168.20.80
Because the round-robin feature of DNS server, Internet users will not access your web server or e-mail intermittantly. Same problem occurs to internal users. When Internet users resolve the Exch1 to 192.168.20.80, they cannot access your servers. When internal users resolve the Exch1 to 24.120.80.80, they cannot ping the address.
Solution:
Another DNS server is set up on the Web server.
The preferred DNS server of public side NIC will be 24.120.80.81.
The preferred DNS server of internal NIC will be 192.168.20.82.