1. Man in the Middle Attack
Cyber Security
Man in the Middle Attack

2. What is the Man in the Middle?
"Man in Middle" Attack is a form of active eavesdropping in which the attacker makes independent connections with the victims and relays messages between them, making them believe that they are talking directly to each other over a private connection when in fact the entire conversation is controlled by the attacker.
The attacker must be able to intercept all messages going between the two victims and inject new and modified messages to one or both of them, which is straightforward in many circumstances

3. Man in the Middle using Ettercap
Ettercap is a suite for man in the middle attacks on LAN. It features sniffing of live connections, content filtering on the fly and many other interesting tricks. It supports active and passive dissection of many protocols (even ciphered ones) and includes many feature for network and host analysis.
Installation
OpenSuSe 11.1 user can use "1-click" installer to install Ettercap

4. Man in the Middle using Ettercap
Running Ettercap
You need to select a user interface (no default) using -T for Text only, -C for the Ncurses based GUI, or -G for the nice GTK2 interface (e.g) - # ettercap –G
Open Ettercap in graphical mode: # ettercap -G
Select the sniff mode: Sniff → Unified sniffing and Scan for host inside your subnet Hosts → Scan for hosts 
See the MAC and  IP addresses of the hosts inside your subnet: Hosts → Hosts List, from this list Select the machines to poison

5. Man in the Middle using Ettercap
Running Ettercap continued…
See the MAC and  IP addresses of the hosts inside your subnet: Hosts → Hosts List, from this list Select the machines to poison
We chose to ARP poison only the windows machine and the router
Highlight the line containing and click on the "target 1" button.
Highlight the line containing and click on the "target 2" button. 
Start the ARP poisoning: Mitm → Arp poisoning and start the sniffer to see the activities

6. Man in the Middle using Ettercap
ARP TRAFFIC before the poisoning:
As you can see that the router and the Windows machine send an ARP broadcast to find the MAC address of the other.
ARP TRAFFIC after the poisoning
The router ARP broadcast request is answered by the Windows machine similarly than in the previous capture.
The difference between the two steps comes from the fact that there is no request coming from Windows ( ) to find the MAC address associated to the router ( ) because the poisoner continuously sends ARP packets telling the Windows machine that is associated to his own MAC address (11:22:33:44:99:99) instead of the router MAC address (11:22:33:44:11:11).