It nor your IP it your MAC Address of the Network card of your PC/Workstation

The MAC Address is the Hexidecimal number you see if you go to a command prompt in Windows and type:

ipconfig /all

You get this:

Windows IP Configuration

Host Name . . . . . . . . . . . . : mypc-donottouch
Primary Dns Suffix . . . . . . . :
Node Type . . . . . . . . . . . . : Unknown
IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No

Ethernet adapter Local Area Connection:

Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Broadcom NetXtreme Gigabit Ethernet
Physical Address. . . . . . . . . : 00-0C-76-2A-4B-91
Dhcp Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
IP Address. . . . . . . . . . . . : 192.168.0.2
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 192.168.0.1
DHCP Server . . . . . . . . . . . : 192.168.0.1
DNS Servers . . . . . . . . . . . : 192.168.0.1
Lease Obtained. . . . . . . . . . : 03 March 2007 15:18:15
Lease Expires . . . . . . . . . . : 06 March 2007 15:18:15

The bit in bold is the MAC Address that Autodesk use.