What protocol is responsible for determining the MAC address associated with each IP address and keeping a table of its results?

ARP is necessary because the software address (IP address) of the host or computer connected to the network needs to be translated to a hardware address (MAC address). Without ARP, a host would not be able to figure out the hardware address of another host. The LAN keeps a table or directory that maps IP addresses to MAC addresses of the different devices, including both endpoints and routers on that network.

This table or directory is not maintained by users or even by IT administrators. Instead, the ARP protocol creates entries on the fly. If a user's device does not know the hardware address of the destination host, the device will send a message to every host on the network asking for this address. When the proper destination host learns of the request, it will reply back with its hardware address, which will then be stored in the ARP directory or table. 

If ARP is not supported, manual entries can be made to this directory. 

ARP spoofing is also known as ARP poison routing or ARP cache poisoning. This is a type of malicious attack in which a cyber criminal sends fake ARP messages to a target LAN with the intention of linking their MAC address with the IP address of a legitimate device or server within the network. The link allows for data from the victim's computer to be sent to the attacker's computer instead of the original destination. 

ARP spoofing attacks can prove dangerous, as sensitive information can be passed between computers without the victims' knowledge. ARP spoofing also enables other forms of cyberattacks, including the following:

A man-in-the-middle (MITM) attack is a type of eavesdropping in which the cyberattacker intercepts, relays, and alters messages between two parties—who have no idea that a third party is involved—to steal information. The attacker may try to control and manipulate the messages of one of the parties, or of both, to obtain sensitive information. Because these types of attacks use sophisticated software to mimic the style and tone of conversations—including those that are text- and voice-based—a MITM attack is difficult to intercept and thwart.

A MITM attack occurs when malware is distributed and takes control of a victim's web browser. The browser itself is not important to the attacker, but the data that the victim shares very much is because it can include usernames, passwords, account numbers, and other sensitive information shared in chats and online discussions. 

Once they have control, the attacker creates a proxy between the victim and a legitimate site, usually with a fake lookalike site, to intercept any data between the victim and the legitimate site. Attackers do this with online banking and e-commerce sites to capture personal information and financial data. 

A denial-of-service (DoS) attack is one in which a cyberattacker attempts to overwhelm systems, servers, and networks with traffic to prevent users from accessing them. A larger-scale DoS attack is known as a distributed denial-of-service (DDoS) attack, where a much larger number of sources are used to flood a system with traffic.

These types of attacks exploit known vulnerabilities in network protocols. When a large number of packets are transmitted to a vulnerable network, the service can easily become overwhelmed and then unavailable. 

Session hijacking occurs when a cyberattacker steals a user's session ID, takes over that user's web session, and masquerades as that user. With the session ID in their possession, the attacker can perform any task or activity that user is authorized to do on that network. 

Authentication occurs when a user tries to gain access to a system or sign in to a restricted website or web service. The session ID is stored in a cookie in the browser, and an attacker engaged in session hijacking will intercept the authentication process and intrude in real time. 

The Fortinet network access control (NAC) solution provides enhanced visibility across all devices in a network to keep up with the ever-evolving threat landscape. NAC is part of the zero-trust network access model for security, in which trust is not a given for users, applications, or devices, whether connected to the network or not, but has to be established.

Each device in a network maintains a copy of the ARP cache, and the cache is cleaned every few minutes. As such, all devices connected to that network must be kept secure so that important data, including IP addresses, are not compromised. To further protect your network devices and servers, Fortinet Ethernet LAN switches safeguard an organization's infrastructure and even include a selector tool to identify the best switch to meet network requirements.