[OpenVPN home] [Date Prev] [Date Index] [Date Next]
[OpenVPN mailing lists] [Thread Prev] [Thread Index] [Thread Next]
Google
 
Web openvpn.net

Re: [Openvpn-users] Duplicate MAC addresses with OSX clients


  • Subject: Re: [Openvpn-users] Duplicate MAC addresses with OSX clients
  • From: James Yonan <jim@xxxxxxxxx>
  • Date: Wed, 5 Oct 2005 13:56:43 -0600 (MDT)


On Wed, 5 Oct 2005, Andrew Boyce-Lewis wrote:

> I am running a bridging network and have discovered that the OSX tun/ 
> tap driver apparently hard codes the MAC address of the tap interface  
> (so all OSX clients have the same address). ( Tiger version http:// 
> www-user.rhrk.uni-kl.de/~nissler/tuntap/ )
> 
> Has anyone else run into this problem? or can anyone suggest any  
> possible workarounds? I've read that the windows and linux tap  
> drivers use an algorithm to generate a non-sense MAC address and  
> assign that to the interface... I suppose that might need to be  
> implemented for the OSX version.

Here are my comments in the TAP-Win32 source code about this.

/*
 * Generate a MAC using the GUID in the adapter name.
 *
 * The mac is constructed as 00:FF:xx:xx:xx:xx where
 * the Xs are taken from the first 32 bits of the GUID in the
 * adapter name.  This is similar to the Linux 2.4 tap MAC
 * generator, except linux uses 32 random bits for the Xs.
 *
 * In general, this solution is reasonable for most
 * applications except for very large bridged TAP networks,
 * where the probability of address collisions becomes more
 * than infintesimal.
 *
 * Using the well-known "birthday paradox", on a 1000 node
 * network the probability of collision would be
 * 0.000116292153.  On a 10,000 node network, the probability
 * of collision would be 0.01157288998621678766.
 */

James

____________________________________________
Openvpn-users mailing list
Openvpn-users@xxxxxxxxxxxxxxxxxxxxx
https://lists.sourceforge.net/lists/listinfo/openvpn-users