You must register your computer's hardware address before your computer can communicate over SUNet. Note that a laptop with wireless capabilities will have TWO hardware addresses, one for the wired connection, and one for the wireless connection.
On a Linux system, you can find the MAC using the command line.
Open up a terminal and enter the command `ipconfig -a`
This will list out all the networking devices and their properties. On the left-hand side, you should see names for each interface such as `eth0` `wla0` or `wlp3s0`. Wireless interface often starts with a `w` while wired ethernet of starts with an `e`.
Find the device you are interested in registering and look for the entry `HWaddr`. This is the hardware or MAC address that you should use to register that networking interface.