Configuring Internal Network Information for Clients
The Client Information tab, shown in Figure 2, allows you to specify DNS settings for VPN clients and routing definitions. The first two text boxes on this page allow you to enter DNS server and search domain settings. Specifying your network’s DNS servers allows users to locate resources on your network by DNS name. When a DNS configuration is provided, clients will use the specified DNS server as opposed to the DNS server of their ISP. Enter DNS information in these fields in the same way that you would in the Network pane of System Preferences or for the DHCP service.
Figure 2 Client Information tab of the VPN Service Settings in Server Admin
The Network Routing Definitions listbox includes all routing definitions that you have configured for the VPN service. To add a routing definition, click the Add (plus sign) button beneath the listbox. To delete or edit a routing definition, select it in the listbox and click the Remove (minus sign) or Edit (pencil icon) button, respectively. When you click the Add button, the routing definition dialog box will ask you to specify a network address range and a subnet mask, and to select whether this will be a public or private routing definition.
A public routing definition is one that specifies that the client should use its Internet connection to access the appropriate address range instead of accessing it using the VPN connection. A private routing definition specifies that the connection is to be made using the VPN connection. Generally, you will specify only private routing definitions for resources within your network. If no routing definitions are specified, all network and Internet connections from the client will go through the VPN connection, which will generate additional traffic for the VPN server and your network’s Internet connection.
IP address ranges entered in routing definitions are entered as a base IP address (such as 126.96.36.199) and then a subnet mask, which defines which digits of that IP address are considered part of the specified range (using the same IP address I just mentioned, 255.255.255.0 would specify that 188.8.131.52 through 184.108.40.206 are part of the range). You can use a subnet calculator to define specific control of which IP addresses are included in an IP address range.
Generally speaking, you will want to define all IP addresses within your network as private network routing definitions. You may also want to define some external sites as private definitions, particularly those that limit access based on the originating IP address as private addresses.