OpenVPN always allowed 8 ACKs in P_ACK_V1 packets but only used
up to 4 in other control packets. Since Softether drops all packets with
more than 4 ACKs it also drops legimate P_ACK_V1.
See also this issue: https://github.com/schwabe/ics-openvpn/issues/1486
Also, the default timeout value is set to 30000 (milliseconds) instead of 10000.
The change is made because it was reported that some routers failed to connect in time.
PROTO_OPTION is a structure that describes an option (who would've guessed?).
It's designed in a way that allows it to occupy as low memory as possible, while providing great flexibility.
The idea is similar to the one implemented in LIST for trivial types, with the difference that PROTO_OPTION doesn't require casting due to the use of union.
As a side effect, the DH parameter is now applied to the TCP server as well.
Previously, the default value was always used, ignoring the one from the configuration.
- An additional parameter is added to IsPacketForMe(), used to specify the protocol type (currently either TCP or UDP).
- SupportedModes() is dropped because it's now redundant.
- IsOk() and EstablishedSessions() are dropped because error checking should be handled by the implementation.
- ProtoImplDetect() now takes a buffer and its size rather than a SOCK, so that it can be used to detect UDP protocols.
- The OpenVPN toggle check is moved to ProtoImplDetect(), so that we don't have to duplicate it once UDP support is implemented.
This allows an OpenVPN client to bypass a firewall which is aware of the protocol and is able to block it.
The XOR mask set on the server has to be the same on the client, otherwise it will not be able to connect with certain obfuscation modes.
A special OpenVPN client built with the "XOR patch" is required in order to use this function, because it has never been merged in the official OpenVPN repository.
Two parameters are added to the server configuration: "OpenVPNObfuscationMethod" and "OpenVPNObfuscationMask".
Their value can be retrieved with "OpenVpnObfuscationGet" and set with "OpenVpnObfuscationEnable" in the VPN Command Line Management Utility.
