A hacker then becomes a man in the middle. To remain undetected, the intercepted data traffic is usually passed on to the actual target system. This system now has the opportunity to record or manipulate all data traffic. The targeted system then links the output IP to the wrong hardware address and sends all future data packets to the hacker-controlled system. As a rule, these data packets contain the MAC address of a network device being controlled by hackers. This is referred to as ARP poisoning, or a вЂњcontaminationвЂќ of the ARP caches. In the context of ARP spoofing, hackers try to preempt the actual target computer in order to send a reply packet with incorrect information and manipulate the ARP table of the inquiring computer.

The request response scheme of ARP protocols is arranged so that the first answer to an ARP request is accepted and stored. What then, if the intended computer doesnвЂ™t reply, but instead the reply comes from another device controlled by an internal attacker with criminal intentions? This is where ARP spoofing comes into play. Communication over the local network is now not prevented by anything. If this ARP reply is delivered to Computer A, then it has all of the information required to send data packets to Computer B. The requested MAC address is aa-aa-aa-aa-aa-aa. Its ARP reply contains the following information: An answer to the broadcast request is only expected from Computer B.

In this way, all computers in the network record the broadcast request along with the accompanying sender address. In these tables, all known MAC addresses are temporarily stored along with their matching IP addresses. In order to prevent an ARP request from being submitted prior to the sending of each data packet, every computer in the network performs a local table, called the ARP cache. The ARP request is received by all computers in the LAN. This request contains the following information:ДЄ computer with the MAC address xx-xx-xx-xx-xx-xx and the IP address would like to get in contact with a computer with the IP address and requires the appropriate MAC address. This uses the Address Resolution Protocol (ARP), a network protocol that operates according to the request response scheme.ДЄfter searching for the appropriate MAC address, Computer A sends a broadcast request (or ARP request) to all devices on the network.

If Computer A wants to contact Computer B within the same network, it must first determine the appropriate MAC address for its IP address. In networks based on IPv4 the address resolution via ARP is unavoidable. But in practice, this doesnвЂ™t work because IPv4 addresses are too short to completely map the MAC address. Theoretically, these hardware addresses would be suitable for global addressing. MAC addresses are assigned by their respective hardware manufacturers and are unique worldwide. These MAC addresses (Media Access Control) are unique 48-bit numbers, and make it possible to identify each device in the LAN via its network card.Д®xample of a MAC address: 00-80-41-ae-fd-7e Instead, they use physical hardware addresses for addressing in local IPv4 networks. Unlike devices on the internet, devices in the LAN donвЂ™t communicate directly via IP addresses.

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