Difference between ethernet address and IP address?

Hey

Can anyone please tell me what is ethernet address and its role in security. If someone knows my PC ethernet address, how would it affect my security? What can he do with that ethernet address?
I have some knowledge about IP address, many ways of tracing and hiding IP, but I don't know if ethernet address can also be traced. I really wanna know ethernet address is useful for what purpose?

Jam it back in, in the dark.

Someone knowing your PC's Ethernet/MAC address might be able to impersonate your PC by MAC spoofing, but only if you're on the same network.

The MAC address is a unique code that identifies a specific network adapter, and thus can identify a particular PC.

How ya doing, buddy?

Well, the MAC is not exactly unique since most ethernet circuit firmwares allow it to temporarly override the MAC address.

The standard MAC address of your card also can give the attacker information about the card you're using and so potential weaknesses this card has.

Another "harmless attack vector": Knowledge about the MAC address gives you the possibility to forge Magic packets that you inject into the network and trigger certain actions inside the card (like e.g. WakeOnLAN) - of course the card has to be active and configured to react on Magic packets.

There can be of course bigger security holes depending on your environment. Example from my campus:
We have several unix machines in each office, hooked up to the local ethernet. Ethernet ports in the office can have different states: fully open, closed, conditionally open

Closed should be pretty clear. Fully open means that you can also hook up your system (your laptop you brought e.g.) to the port and it receives an IP through DHCP and you have full access to the network + internet.

Conditionally open: I found that out because I tried to hook up my laptop to one of the ports. Back then I didn't knew the different states of ports. However I didn't get an IP when disconnecting my office desktop system from the port and connecting my laptop.
In the end I tried MAC spoofing (plus some other techniques which I learned from monitoring the traffic between the desktop system and the network) and finally received my IP via DHCP.

This shows that you can gain some advantages from knowing the MAC, but it highly depends on your network. And even for me it wasn't really that much of an advantage - I eventually disclosed the vulnerability to our computer laboratory staff and requested to fully open a closed port in the office.

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