VPN on demand is a brilliant Apple feature that makes VPN connection able to start without the need to go into settings or leaving the application you are using. iOS only backs VPN On Demand for networks that use certificate for authentication. You have to use a configuration profile to appoint which domains need a VPN connection.
This connection is made whenever the appliance attempts to connect to specific domains.
Certain apps need to do nothing; the minute they attempt to access such a server the VPN connection starts.
You can install the VPN On Demand feature to make the iPad or iPhone set a VPN connection automatically when the user attempts to host on a list you provide or access a domain.
This trait is fantastic for knowing that the iPad and iPhone use VPN connections constantly for connecting to the corporate network.
To install VPN On Demand, From the VPN pane choose Enable VPN On Demand. Then obey these steps to establish the list of hosts and domains for which you want to dominate VPN connections:
Select the (Add) button at the Domain And Host Names, a VPN list box will be established.
In the parallel Domain Or Host column, enter the domain or host name.
A pop-up menu in the On Demand Action column will appear, open it, and select the convenient setting:
Select Always Establish setting to make the iPad or iPhone set a VPN connection.
Select Establish If Needed setting to make the iPad or iPhone attempt a DNS lookup and set a VPN connection if returns no match.
Select Never setting to block initiating VPN connection for the domain or host. If it has already initiated a VPN connection, it can employ the connection for this domain or host. Keep doing those three steps to add to the list different hosts and domains.
Read more about VPN on demand for iOS HERE