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Re: [Openvpn-users] dhcp-renew fails using a remote DHCP server


  • Subject: Re: [Openvpn-users] dhcp-renew fails using a remote DHCP server
  • From: James Yonan <jim@xxxxxxxxx>
  • Date: Tue, 5 Oct 2004 06:12:19 -0600 (MDT)


On Tue, 5 Oct 2004, Mathias Sundman wrote:

> I'm experimenting with the "Media Status" = Always Connected on the TAP 
> device (on Windows XP).
> 
> When using this, I found --dhcp-renew and --dhcp-release useful, to have 
> the adapter release and renew the IP when starting/stopping diffrent 
> openvpn tunnels.
> 
> All my configurations work fine with this except for one, where I use a 
> DHCP server on the remote network, and bridges that to my TAP interface.
> 
> I'm using the check-mac trick to hand out IP adresses without a default gw 
> from my DHCP server.
> 
> This worked fine, when Media Status was set to Application Controlled, and 
> I did not use dhcp-renew, but now it doesn't. I just don't get any IP 
> address.
> 
> Sniffing the TAP device with windump, it seems like no DHCP request is 
> beeing sent.
> 
> So OpenVPN just keeps repeating:
> 
> Tue Oct 05 13:09:32 2004 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
> Tue Oct 05 13:09:32 2004 Route: Waiting for TUN/TAP interface to come up...
> Tue Oct 05 13:09:33 2004 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
> Tue Oct 05 13:09:33 2004 Route: Waiting for TUN/TAP interface to come up...
> Tue Oct 05 13:09:34 2004 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
> Tue Oct 05 13:09:34 2004 Route: Waiting for TUN/TAP interface to come up...
> Tue Oct 05 13:09:36 2004 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
> Tue Oct 05 13:09:36 2004 Route: Waiting for TUN/TAP interface to come up...
> Tue Oct 05 13:09:37 2004 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
> 
> until it times out.
> 
> Running ipconfig /renew tap-dev gives me an IP adress though...
> 
> Is there perhaps a bug that --dhcp-renew only works with the internal DHCP 
> server in the TAP driver?

--dhcp-renew is a simple call to the IP helper API.  The implementation is 
internal to Windows.

You might want to try running the debug version of TAP-Win32:

http://openvpn.sourceforge.net/beta/

This will give you a detailed picture of the operation of the internal
DHCP server.

> Another related thing I've always wondered but not asked is:
> 
> Does OpenVPN or the TAP driver block DHCP requests from passing the tunnel 
> when using the internal DHCP server in the TAP driver, or how do we make 
> sure the internal DHCP server answers the DHCP requests, and not the DHCP 
> server on the remote bridged network?

The internal DHCP server should take priority over any remote DHCP server 
when the adapter is ioctled with TAP_IOCTL_CONFIG_DHCP_MASQ, which is 
triggered by --ip-win32 dynamic.

James

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