[Openvpn-users] Re: No TAP-Win32 adapter in XP SP2

[Scott Hughes <shughes@xxxxxxxxx>]

James Yonan <jim <at> yonan.net> writes:
> While I'd certainly like to get to the bottom of this latest
> disappearance, you should also understand that having the icon is not
> necessary for OpenVPN to function.  Some people even hide it on purpose.  
> OpenVPN doesn't care if the icon exists and will even let you choose a
> hidden adapter using the "dev-node" directive, by referring directly to
> the device GUID.  In most cases, you don't even need the "dev-node"  
> directive.  OpenVPN will automatically find a free TAP-Win32 adapter, even
> one that lacks an icon.

Yes, I did notice that.  I've got no problem with OpenVPN and the TAP-Win32
adapter in general, both excellent and I applaud your efforts for making this
tool...  I'm just stuck on that pesky last step of getting the ethernet bridging
to work.

> Just for reference, here is my current understanding of the hidden adapter 
> issue:
> 
> Windows provides a "feature" that allows a device driver to indicate in 
> it's INF file that it would like to be hidden.  For example in the 
> TAP-Win32 INF file, we have:
> 
> ;----------------- Characteristics ------------
> ;    NCF_PHYSICAL = 0x04
> ;    NCF_VIRTUAL = 0x01
> ;    NCF_SOFTWARE_ENUMERATED = 0x02
> ;    NCF_HIDDEN = 0x08
> ;    NCF_NO_SERVICE = 0x10
> ;    NCF_HAS_UI = 0x80
> ;----------------- Characteristics ------------
> 
> [tap0801.ndi]
>    CopyFiles       = tap0801.driver, tap0801.files
>    AddReg          = tap0801.reg
>    AddReg          = tap0801.params.reg
>    Characteristics = 0x81
> ;--------------------------------------------
> 
> If the registry item "Characteristics" has the NCF_HIDDEN (0x08) bit set,
> the adapter will be hidden (e.g. Characteristics = 0x89). It also seems
> that there are other, undocumented triggers which will cause the adapter
> icon to be hidden, such as length of the HWID string.  There may be even 
> additional undocumented triggers that we don't know about.
> 
> One thing that might be worth checking is to verify that the 
> "Characteristics" registry entry for the device is in fact 0x81.

Checked Characteristics in the registry, and it's 0x81 like it should be.

This got me experimenting with some registry kung-fu (I'm okay with a fresh
re-install, so I don't mind hacking registry values that I don't understand).  I
hunted down the entry that gave the "name" to my "Local Area Connection"..
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Network\
   {4D36E972-E325-11CE-BFC1-08002BE10318}\{$MY_LAN_GUID}

There was no entry there with the TAP-Win32 GUID, so I created one and gave it a
name.  Now my cli output looks better (used to show null and throw a warning
about no link in Network Connections):

$ openvpn --show-adapters
Available TAP-WIN32 adapters [name, GUID]:
'OpenVPN' {B2DB1117-F3C6-4110-AE92-70D7BB4795BB}

But...  Still no link in Network Connections.  Even after a reboot.  So, there's
some other reference I'm missing..  But it looks like my registry entry filled
in the place openvpn was checking for the name and whether or not it was linked
in.  So, now there is yet another piece to the puzzle.

> It might also be worth checking out this newsgroup:
> 
> http://groups-beta.google.com/group/
>    microsoft.public.development.device.drivers
> 
> This is where most driver development discussion takes place.  MS 
> employees are active in the group.

I asked on the OpenVPN users list in the hopes that the solution was so trivial,
nobody bothered mentioning it before...  I'm hesitant to post on a driver
development site, since I don't fully understand what the TAP-Win32 adapter
_should_ be doing, much less why it isn't doing it for only me.  I'll wait a few
days to see if any users pipe up who've worked around the same issue...  If I
don't hear of a solution, I'll just do a re-install.

Thanks for your help...

Scott Hughes


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