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-This file documents the support in OpenVPN for Android 4.0 and up.
-
-This support is primarily used in the "OpenVPN for Android" app
-(http://code.google.com/p/ics-openvpn/). For building see the developer
-README: http://code.google.com/p/ics-openvpn/source/browse/doc/README.txt.
-
-Android provides the VPNService API
-(http://developer.android.com/reference/android/net/VpnService.html)
-which allows establishing VPN connections without rooting the device.
-
-Since all the interfaces are are Android specific the calls to this
-interface are made from the UI instead of OpenVPN directly. The API
-needs the following parameters:
-
-- IP and netmask of tun interface
-- Networks that should be routed to the tun interface
-- DNS Servers and DNS Domain
-- MTU
-
-All IPs/Routes are in CIDR style. Non CIDR routes are not supported.
-Notable is the lack of support for setting routes to other interfaces
-usually used to avoid the server connection going over the tun
-interface. The Android VPNService API has the concept of protecting
-a socket from being routed over a interface. Calling protect (fd)
-will internally bind the socket to the interface used for the
-external connection (usually WiFi or mobile data).
-
-To use OpenVPN with the VPNService API OpenVPN must be build with
-the TARGET_ANDROID compile option. Also the UI must use a UNIX
-domain socket to connect to OpenVPN. When compiled as TARGET_ANDROID
-OpenVPN will use management callbacks instead of executing traditional
-ifconfig/route commands use the need-ok callback mechanism which
-will ask
-
-> NEED-OK command
-
-where command can be:
-
-IFCONFIG6 IPv6/netmask
-IFCONFIG local remoteOrNetmask MTU topology
-
-To tell the UI which IPs addresses OpenVPN expects on the interface.
-Topology is one of "net30","p2p","subnet" or "undef".
-
-ROUTE6 network/netmask
-ROUTE network netmask
-
-To tell the UI which routes should be set on the tun interface.
-
-DNSSERVER serverip
-DNSDOMAIN searchdomain
-
-To set the DNS server and search domain.
-
-The GUI will then respond with a "needok 'command' ok' or "needok
-'command' cancel', e.g. "needok 'IFCONFIG' ok".
-
-PERSIST_TUN_ACTION
-
-In Android 4.4-4.4.2 a bug exists that does not allow to open a new tun fd
-while a tun fd is still open. When OpenVPN wants to open an fd it will do
-this query. The UI should compare the last configuration of
-the tun device with the current tun configuration and reply with either (or
-always respond with OPEN_AFTER_BEFORE/OPEN_BEFORE_CLOSE)
-
-- NOACTION: Keep using the old fd
-- OPEN_AFTER_CLOSE: First close the old fd and then open a new to workaround the bug
-- OPEN_BEFORE_CLOSE: the normal behaviour when the VPN configuration changed
-
-For example the UI could respond with
-needok 'PERSIST_TUN_ACTION' OPEN_AFTER_CLOSE
-
-To protect a socket the OpenVPN will send a PROTECTFD to the UI.
-When sending the PROTECTFD command command to the UI it will send
-the fd of the socket as ancillary message over the UNIX socket.
-The UI will then call protect(fd) on the received socket protecting
-it from being routed over the VPN.
-
-When opening a tun device the OpenVPN process will first send all
-route, ifconfig and DNS related configuration to the UI and after
-that calls the OPENTUN command to receive a tun fd with the requested
-configuration. The UI will than use the collected information to
-call the VPNService's establish() method to receive a fd which in
-turn is send to the OpenVPN process as ancillary message to the
-"needok 'OPENTUN' ok' response.
-
-The OpenVPN for Android UI extensively uses other features that
-are not specific to Android but are rarely used on other platform.
-For example using SIGUSR1 and management-hold to restart, pause,
-continue the VPN on network changes or the external key management
---management-external-key option and inline files.