Which hardware (MAC) address will be used for DHCP over VPN with SonicWALL devices?
VPN Tracker always bases its MAC address on the en0 (*) interface's MAC address, independent from the actual network interface that is being used (e.g. Ethernet, AirPort, Modem, ...). This permits administrators to make reservations for specific IP addresses on the DHCP server for the VPN Tracker clients, no matter which of their network interfaces they currently use.
In order to prevent conflicts when your Mac is simultaneously connected to one of your SonicWALL's network interfaces through en0 (or has been connected shortly before establishing the VPN connection), VPN Tracker uses a slightly modified version of your en0 interface's MAC address :
The second least significant bit of the most significant byte of the MAC address is set to 1. According to the standard, setting this bit to 1 signifies a self-assigned MAC address (instead of the factory-assigned one), this ensures that there are no conflicts with other factory-assigned MAC addresses.
Example:
Original MAC address: 00:1b:63:B7:42:23
VPN Tracker MAC address: 02:1b:63:B7:42:23
(*) If your Mac does not have an en0 interface, VPN Tracker uses the next higher one.