DNS server split principle
DNS split is required when you need to provide some resources both internal (intranet) and external (internet) using the same name.
Simple DNS zone
Let's start with a simple reminder.
A standard DNS zone is only internal = no one access any internal resources from the outside. If you want to do so, you have to use a VPN connection.
The Internet connection is just OUT.
Limitations
Sometimes you can use the same name on 2 different locations. Therefore, some resources are only accessible when you are inside or outside.
Another problem might occurred when you want to make an internal resource available from both the inside AND the outside.
DNS split is required when the internal domain name matches an external name.
