Pushing DHCP options to clients

The OpenVPN server can push DHCP options such as DNS and WINS server addresses to clients (some caveats to be aware of). Windows clients can accept pushed DHCP options natively, while non-Windows clients can accept them by using a client-side up script which parses the foreign_option_nenvironmental variable list. See the man page or openvpn-users mailing list archive for non-Windows foreign_option_n documentation and script examples.

For example, suppose you would like connecting clients to use an internal DNS server at 10.66.0.4 or 10.66.0.5 and a WINS server at 10.66.0.8. Add this to the OpenVPN server configuration:

push "dhcp-option DNS 10.66.0.4"
push "dhcp-option DNS 10.66.0.5"
push "dhcp-option WINS 10.66.0.8"

To test this feature on Windows, run the following from a command prompt window after the machine has connected to an OpenVPN server:

ipconfig /all

The entry for the TAP-Windows adapter should show the DHCP options which were pushed by the server.

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