What Is a MAC Flooding Attack?

Updated on February 14, 2025

A MAC flooding attack is a network threat that targets switches by overloading their MAC address table with fake addresses. This forces the switch to send traffic to all ports instead of the correct destination. As a result, attackers can intercept data and disrupt the network, causing slower performance, unauthorized access, and potential data breaches for businesses.

This article explains how MAC flooding attacks work, the risks they pose to networks, and simple steps to detect and prevent them.

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Definition and Core Concepts

What Is a MAC Flooding Attack?

A MAC flooding attack is a network threat that targets the limited storage of a switch’s MAC address table. The attacker sends a large number of packets with fake or random MAC addresses, quickly filling up the table. Once it overflows, the switch can no longer forward traffic directly to the intended device. Instead, it broadcasts all incoming traffic to every port, making all data visible to connected devices and creating a major security risk.

What Is a MAC Address Table?

A MAC address table is a key component of a network switch, storing mappings between MAC addresses (unique hardware identifiers for devices) and corresponding switch ports. This table enables the switch to efficiently and securely forward packets to only the intended device by referencing its specific port.

Switch Behavior During an Attack

When a MAC flooding attack occurs:

1. The table becomes overwhelmed by the sheer number of spoofed MAC addresses.
2. Once full, the switch can no longer map new MAC addresses to ports.
3. Incoming packets are broadcast to all ports, allowing any device in the network to intercept the traffic.

This behavior directly undermines the role of a switch as a secure networking device and places both performance and data integrity at risk.

How MAC Flooding Attacks Work

Attack Process

The step-by-step breakdown of a MAC flooding attack is as follows:

1. The attacker generates a high volume of Ethernet frames, each with a spoofed, unique MAC address.
2. These frames are sent to the network switch at rapid intervals.
3. The switch begins to populate its MAC address table until the storage capacity is exhausted.
4. Unable to store additional entries, the switch defaults to broadcasting all traffic.

Switch Behavior Post-Attack

When the MAC address table is full, the switch switches from unicast forwarding mode (sending data to a single recipient) to broadcast mode (sending data to all devices connected to its ports). This significantly increases the network’s vulnerability.

Exploitation of Broadcast Traffic

Broadcast mode allows attackers to:

• Eavesdrop on sensitive business communications and data.
• Intercept credentials such as usernames and passwords.
• Redirect traffic for malicious purposes, including perpetuating further attacks like credential harvesting or social engineering.

Attackers can exploit broadcast traffic to gain unauthorized access to sensitive data while also causing network congestion and disruption.

Key Features of MAC Flooding Attacks

Resource Overload

MAC flooding attacks exploit the finite storage capacity of a switch’s MAC address table. By overwhelming this resource, attackers create network conditions that are conducive to interception and disruption.

Traffic Exposure

Forced to broadcast all traffic, the compromised switch behaves like a network hub, exposing all transmitted data to every connected device. Sensitive communications, file transfers, and proprietary business data are no longer private but instead accessible to unauthorized parties.

Stealthiness

MAC flooding attacks are often difficult to detect in their early stages. Unless network monitoring tools or logging systems are in place, administrators may only notice the problem after network performance significantly degrades or data is compromised.

Use in Combination Attacks

MAC flooding is rarely the end goal. Instead, it is often a precursor to more sophisticated attacks, such as:

• Man-in-the-Middle (MITM) attacks to intercept, alter, or impersonate communications.
• Data theft by capturing sensitive packets transmitted during the broadcast phase.

Without preventative measures, these attacks can lead to cascading security failures.

Risks Associated with MAC Flooding

Data Exposure

MAC flooding attacks put confidential information at serious risk by overwhelming a network switch with fake MAC addresses. This forces the switch into a fail-open mode, sending traffic to all ports instead of the intended recipients. As a result, sensitive data like financial records, trade secrets, or personal information (PII) can be intercepted by attackers. This can lead to data breaches, financial losses, and damage to an organization’s reputation.

Denial of Service (DoS)

By overloading a network switch, attackers can disrupt its functionality and block legitimate traffic. This causes serious issues like packet loss, increased delays, or even a complete denial of service for authorized users. Such disruptions can cripple operations by preventing users from accessing critical services, making strong network security measures essential.

Network Disruption

MAC flooding attacks flood a network with fake MAC addresses, overloading the switch’s CAM table and causing congestion. This leads to slower response times, delays, and instability. Critical applications may be interrupted, and overall productivity and efficiency can suffer. In severe cases, the entire network can grind to a halt, disrupting communication both internally and externally.

Unauthorized Access

When network traffic is broadcast to all devices, attackers can intercept sensitive information they wouldn’t normally have access to. This includes login credentials, private data, or communications meant for restricted systems. Such unauthorized access can compromise the security of the entire network and lead to further exploitation.

Identifying and Mitigating MAC Flooding Attacks

Detection Techniques

Use of Network Monitoring Tools

Tools like Wireshark allow administrators to detect unusual spikes in MAC address changes, which are indicative of flooding attacks.

Switch Logs

Monitor switch logs for excessive and rapid MAC address changes. Most managed switches report these anomalies, making it easier to identify malicious activity.

Prevention Methods

Enable Port Security

Set a maximum number of MAC addresses allowed on each port to prevent attackers from overwhelming the MAC address table. Configure switches to shut down affected ports if the limit is exceeded.

Use VLAN Segmentation

Segregate the network into multiple Virtual Local Area Networks (VLANs) to isolate traffic and minimize the impact of a flood affecting a single VLAN.

Configure Dynamic ARP Inspection (DAI)

Activate Dynamic ARP Inspection to identify and restrict spoofed ARP packets, adding an extra layer of traffic validation.

Regular Network Audits

Perform regular security audits to identify vulnerabilities and ensure that switches are configured according to best practices.

Tools and Techniques for Protection

Managed Switch Features

Modern switches often come equipped with security features such as:

• Port security
• DHCP snooping
• Enhanced logging capabilities

Enabling these features provides automated protection against many MAC flooding tactics.

Intrusion Detection Systems (IDS)

Deploying IDSs with capabilities specific to network traffic analysis helps detect and neutralize MAC flooding attempts in real time.

Security Policies

Develop and enforce stringent policies that restrict unauthorized device connections and limit access to physical networking equipment.

Use Cases and Real-World Examples

Corporate Networks

A poorly secured enterprise switch can be targeted by a MAC flooding attack, potentially exposing sensitive data like financial transactions or business strategies.

Educational Institutions

University networks are especially at risk due to frequent user turnover and less controlled access. A MAC flooding attack could disrupt open-access networks, especially during busy times.

Public Networks

Public Wi-Fi in places like coffee shops or airports often lacks proper security, making it an easy target for attackers using MAC flooding to exploit unprotected users.

Glossary of Terms

• MAC Flooding Attack: A network attack that overloads a switch’s MAC address table with spoofed entries.
• MAC Address Table: A switch’s internal table that maps MAC addresses to specific ports for unicast traffic.
• Port Security: A feature that limits the number of MAC addresses per port, preventing excessive entries.
• Dynamic ARP Inspection (DAI): A security feature that verifies ARP requests and responses to counteract ARP spoofing.
• Broadcast Mode: A state in which a switch sends data packets to all connected devices due to an overloaded MAC table.
• Man-in-the-Middle (MITM) Attack: A type of attack where the attacker intercepts and manipulates communication between two devices.
• DHCP Snooping: A security measure that prevents rogue DHCP servers from assigning IP addresses in a network.

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