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What is MACsec?

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In today’s interconnected world, where data traverses networks constantly, ensuring transmission security is paramount. Enter MACsec, short for Media Access Control Security. It’s a robust protocol that operates at the MAC layer of Ethernet communication, offering a comprehensive suite of security features. Through encryption, MACsec shields data from unauthorized access, while integrity protection mechanisms ensure that transmitted data remains unchanged and authentic. Additionally, MACsec provides authentication capabilities, verifying the identities of communicating parties to prevent spoofing attacks.

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What is MACsec?

MACsec, or Media Access Control Security, is a network security protocol that operates at the Media Access Control (MAC) layer of Ethernet communication. It offers encryption, integrity protection, and authentication for Ethernet frames, ensuring that data transmitted between network devices remains confidential, unaltered, and authenticated. By encrypting Ethernet frames, MACsec prevents unauthorized access to network traffic, while its integrity protection detects any modifications to data during transmission. Additionally, MACsec authentication mechanisms verify the identity of participating network devices, establishing secure communication channels between trusted endpoints. Overall, MACsec strengthens network security by providing end-to-end protection for Ethernet communication, safeguarding sensitive data, and maintaining the integrity of network infrastructure.


MACsec: The Foundation for Network Security

One of the most compelling cases for MACsec is that it provides Layer 2 (OSI data link layer) security, allowing it to safeguard network communications against various attacks, including denial of service, intrusion, man-in-the-middle, and eavesdropping.

These attacks exploit Layer 2 vulnerabilities and often cannot be detected or prevented by higher-layer security protocols. In this way, MACsec provides the foundational security on which a network security architecture can be built.


The OSI model partitions a communication system into seven layers. Each abstraction layer serves the layer above and is served by the layer below.

From a security standpoint, each layer can secure its activities and those above it, but it depends on the security of the layers below. Since Layer 2 is where communication begins, security here establishes the foundation for security for the entire network stack.


Where is MACsec used?

Ethernet has become the ubiquitous communication solution from the desktop to the carrier network.

A growing torrent of network traffic has driven rapid advancements in the performance of Ethernet, with 800G Ethernet representing the latest milestone in the evolution of the standard.

With MACsec as the foundational security technology for safeguarding data in motion across Ethernet networks, the use cases are many:


  • WAN/MAN routers
  • Data center routers and switches
  • Server, storage, and top-of-rack switches
  • LAN switches
  • Secure endpoints such as security cameras and industrial robots


How does MACsec work?

MACsec operates within the Data Link Layer, functioning as a client of the Ethernet Media Access Control (MAC) layer. It enhances Ethernet frames by appending a 16-byte Security Tag (SecTAG) and a 16-byte Integrity Check Value (ICV), using a distinct EtherType (0x88E5), as shown in the given figure. The Ethernet frame includes the preamble and Cyclic Redundancy Check (CRC) before transmission at the MAC layer. Data security is ensured through a combination of integrity checks and encryption methods, specifically MACsec Authentication, Confidentiality, and Integrity.



Architecture of a MACsec Network

In a MACsec-protected network, each node has at least one transmit secure channel. This transmit secure channel is associated with the secure channel identifier (SCI). The transmit secure channel also stores various configuration parameters, such as whether to perform replay protection or enable encryption.

Each node that expects to receive traffic sent through a particular transmit secure channel must configure a matching receive secure channel. This receive secure channel must have a SCI corresponding to the SCI of the transmit secure channel of the peer.

Secure associations are defined within each secure channel (both transmit and receive). The secure associations hold the encryption keys and are identified by their association number. Another critical parameter is associated with each secure association: the packet number. On the transmit side, this packet number is put in the MACsec header and used in the encryption process. On the receive side, the packet number from the MACsec header can be checked against the packet number locally stored in the corresponding secure association to perform replay protection.


The Advantages of MACsec

In addition to providing foundational level network security, MACsec offers many other advantages:


  • Scalability: MACsec is very scalable and can be deployed in different ways than other cryptographic protocols such as TLS and IPsec. The algorithm used within the MACsec protocol is very suitable for high network speeds. It also has low latency because the cryptographic algorithm employed allows the starting of processing of the head of the packet without knowing the tail of the packet.


  • No software intervention: The MACsec protocol can be fully implemented in hardware without software intervention. IPsec, TLS, or any other protocol requires the interaction of software.


  • Full-speed operation: Another compelling advantage of MACsec is that it operates at a t-line rate. Speed is critical as networks and data centers need all the bandwidth they can get to handle the deluge of data traffic. Line rate operation means networks can get the robust Layer 2 security of Media Access Control Security without sacrificing performance.


  • Device-to-device security: MACsec establishes secure data transfer between two devices regardless of the intervening devices or network. This has allowed MACsec to be used in LANs, MANs, and WANs to secure data communication.


  • Connectionless data integrity: Unauthorized changes to data can only be made after being detected. Each MAC frame carries a separate integrity verification code, hence the term connectionless.


  • Data origin authenticity: A received MAC frame is guaranteed to have been sent by the authenticated device.


  • Confidentiality: The data payload of each MAC frame is encrypted to prevent it from being eavesdropped by unauthorized parties.


  • Replay protection: MAC frames copied from the network by an attacker cannot be resent into the network without detection. Limited replay can be permitted in particular configurations with the possibility of frame reordering within a network.


  • Bounded receive delay: MAC frames cannot be intercepted by a man-in-the-middle attack and delayed by more than a few seconds without being detected.



As stated earlier, MACsec only operates on layer 2, so it can only protect a single LAN and offers no protection when traffic is routed. This single LAN can be a physical LAN or a virtual LAN, such as those provided by overlay network technologies like VXLAN, GENEVE, etc.

MACsec also cannot protect against malicious layer 3 traffic from a different network interface on a machine connected to multiple LANs. For example, attacks that rely on forcing traffic to leave from other interfaces, using ARP spoofing or IP redirects, cannot be prevented using MACsec alone. As always, with security-related matters, careful configuration is necessary to eliminate flaws that weaken the setup.



In conclusion, MACsec is a robust security protocol operating at the MAC layer of Ethernet communication, providing encryption, integrity protection, and authentication for network traffic. By encrypting Ethernet frames and ensuring data integrity, MACsec offers end-to-end security, making it an essential component in safeguarding sensitive information and maintaining the integrity of network infrastructure. With its architecture supporting secure channels and associations, MACsec facilitates secure communication between trusted endpoints, protecting against unauthorized access and data tampering. While MACsec excels in LAN environments and is compatible with tunneling technologies like VXLAN, it must acknowledge its limitations in protecting against layer 3 attacks and its confinement to a single LAN. Overall, MACsec remains a valuable tool in bolstering network security and ensuring the confidentiality and integrity of data transmission.




  1. What is the primary use case for MACsec?

The primary use case for MACsec is to secure standard LAN environments, where multiple machines connected to the same LAN exchange encrypted packets, ensuring data transmission confidentiality and integrity.


  1. How does MACsec compare to other security protocols like IPsec and SSL/TLS?

MACsec operates at the MAC layer of Ethernet communication, providing end-to-end security for LAN environments, while IPsec operates at layer 3 and SSL/TLS operates at the application layer. While MACsec excels in securing Ethernet frames and protecting against layer 2 attacks, IPsec and SSL/TLS offer security at higher layers of the OSI model, with IPsec focusing on IP packet encryption and SSL/TLS providing application-layer encryption for specific applications.


  1. What are the limitations of MACsec?

MACsec is limited to protecting a single LAN and offers no protection when traffic is routed beyond the LAN. Additionally, it cannot protect against layer 3 attacks from malicious traffic originating from other network interfaces on a machine connected to multiple LANs. Careful configuration is necessary to address these limitations and ensure robust network security.

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