@keyser Thank you for your reply! Yes, I need those options for split routing.
The Windows VPN client is just capable of class based routing and ignores pushed routes. So per default it just adds a class based route to the remote net and ignores everything else except ip address.
Here is an excerpt from the Strongswan documentation:
Split Routing since Windows 10
Microsoft changed the Windows 10 VPN routing behavior for new VPN connections. Option "Use default gateway on remote network option" in the Advanced TCP/IP settings of the VPN connection is
now disabled by default but can be enabled if desired. Fortunately Windows sends a DHCP request upon connection and add routes supplied in option 249 of the DHCP reply.
Sample configuration file for dnsmasq:
dhcp-vendorclass=set:msipsec,MSFT 5.0
dhcp-range=tag:msipsec,192.168.103.0,static
dhcp-option=tag:msipsec,6
dhcp-option=tag:msipsec,249, 0.0.0.0/1,0.0.0.0, 128.0.0.0/1,0.0.0.0
where 192.168.103.0 is your (internal) network. It pushes two separate routes which cover the entire IPv4 range. Gateway could be anything (set to 0.0.0.0 in an example) as it is ignored by Windows. Note that you can’t ignore DHCP routes in Windows.
Strongswan Documentation for Windows clients
In my opinion this can only be achieved with the dhcp plugin. So for supporting Windows clients without configuring something manually, you need dhcp.