Wireshark is a successor of ethereal. Ethereal has been replaced by wireshark due to security vulnerabilities and the assumption that Ethereal is not being developed further.

Is an Ethernet protocol analyzer that helps you explore what is going on on your LAN, WAN, WLAN.

In the days of coax cable lots of computer shared a single wire. Now there are RJ45 connectors and physical Ethernet is point to point. Your Ethernet is probably connected to a Ethernet switch. If you want to sniff whats going on, you not get all the traffic, you just get what is for you: Broadcasts and your IP.

Note: If you have two Ethernet cards in the computer you have two IP addresses