Hi Soulpancake.
LDAP integration via a MID-server requires you to install a java application called MID-server. This is usually done in the same network as the domain controller that the LDAP integration will be pointed towards.
The MID-server collects all the records required from the AD and then sends them to the ServiceNow instance.
When you set up an LDAP integration via a VPN tunnel the communication is initiated by the ServiceNow instance directly to the AD.
For more in-depth information you can read the official ServiceNow documentation:
https://docs.servicenow.com/bundle/jakarta-platform-administration/page/integrate/ldap/concept/c_LDAPIntegrationViaMIDServer.html
https://docs.servicenow.com/bundle/geneva-servicenow-platform/page/integrate/ldap/concept/c_LDAPIntegration.html
https://docs.servicenow.com/bundle/geneva-servicenow-platform/page/integrate/ldap/reference/r_SecureLDAPConnections.html
