On Sunday June 5, j...@yonan.net wrote: > > I don't think it's possible for the current TAP-Win32 driver to do OSI > Layer 3 with a network/netmask setting. This gets back to the same reason > why --ifconfig-pool-linear doesn't work on Windows: The TAP-Win32 driver > is a TAP driver from the perspective of the kernel. The point-to-point > Layer 3 capability is provided by glue code in the driver which makes a > /30 subnet appear to be two point-to-point endpoints. But it doesn't > change the fact that the driver is a TAP driver and will be treated as an > 802.3 network interface by the Windows kernel. > > This means that if you set your TAP driver properties to 192.168.0.0/24 > and you try to ping 192.168.0.66, the network stack will send out an ARP > to find out the MAC address of 192.168.0.66, because we are operating on > OSI Layer 2. While, you might say, why not answer the ARP virtually, so > that point-to-point Layer 3 semantics are operating under the hood. Well > that's exactly what the tun emulation mode in the current TAP-Win32 driver > does. And this is where the /30 subnet limitation comes from.
Why is there a /30 limitation? I cannot see that a /24 subnet could not work just as easily. I see from tapdrvr.c that currently the auto-arp-response will only respond to arp requests for one particular address. But I cannot see why it couldn't trivially be changed to work for any address. i.e. if an arp request appears on the interface for any address (other than the address of the interface), then respond with a reply giving the same virtual MAC address. Surely with would allow the TAP-Win32 driver to act line a tun driver with a subnet mask. And this is, in my mind, the goal. I don't want the TAP-Win32 drive to act like a true point-to-point interface (I can see that that is non-trivial). I just want win32 to have a tun-like interface onto a subnet. That subnet being the subnet that OpenVPN is managing. I'm very nearly tempted to try this out myself, but having never actually compiled anything for WIN32, I dread the learning curve.... NeilBrown
