Advanced VPN Configuration in System Preferences
Typically, VPN servers provide remote computers with all the network address and related information they need. This information can also be entered manually in the Network pane of System Preferences. To do so, launch System Preferences and select the Network pane. Each VPN connection configured on the Mac will be displayed as a network port. You can select the appropriate connection and then select the manual tab to enter static network information for the connection, as indicated in Figure 4.
Figure 4 Entering static/custom network details for a VPN connection