MC-LAG on DmOS: High Availability and Scalability in Network Infrastructures


With the recently released version 9.2 of DmOS, we seek to explore and introduce significant features to optimize network performance and resilience. One of the most notable additions in this update is the MC-LAG (Multi-Chassis Link Aggregation Group) protocol, which stands out for offering high availability and scalability in network infrastructures.

MC-LAG was designed to meet the specific demands of modern networks. Its standardization was established by the IEEE 802.1AX-2014 standard, also referred to as IEEE 802.3ad, which describes the Link Aggregation Control Protocol (LACP).

In this article, we will give an overview of MC-LAG, discussing its central aspects and advantages. Furthermore, we will differentiate MC-LAG from other link aggregation technologies, such as LACP and VSS. At the end, we will show how to configure the protocol in DmOS.


Definition and Functioning

MC-LAG is a protocol that allows multiple switch or router chassis to be grouped into a single logical group, providing high availability and resilience to the network. Through link aggregation, devices are interconnected through redundant physical links, forming a logical group. Traffic is distributed between the chassis transparently, ensuring continuity of services even in the event of a failure in one of the devices.


Benefits of MC-LAG:

  • High Availability: MC-LAG offers hardware redundancy, allowing devices to continue operating even in the event of failures. With automated fault detection, traffic is redirected to operational chassis, minimizing downtime.
  • Scalability: By grouping multiple chassis into a single logical group, MC-LAG makes it easy to add capacity to the network, without the need to replace or reconfigure the entire infrastructure. This provides more flexible and efficient scalability.
  • Load Balancing: Link aggregation in MC-LAG allows load balancing between devices, optimizing the use of network resources and avoiding bottlenecks on individual links.
  • Hardware and Software Requirements: To implement MC-LAG, it is necessary to use switches or routers compatible with the protocol and that support specific features, such as state synchronization between chassis, automated failure detection and recovery.
  • Protocols Involved: MC-LAG uses protocols such as LACP (Link Aggregation Control Protocol) to form the aggregation of logical links between chassis. LACP is responsible for establishing and maintaining link synchronization, ensuring the integrity and reliability of the aggregation.


 Important Challenges and Considerations: When designing and implementing MC-LAG, it is crucial to consider some relevant challenges and issues, such as:

  • Proper Configuration: It is necessary to carefully define the MC-LAG parameters, such as the number of physical links to be aggregated, the distribution of traffic between the chassis and the priorities of each link.
  • State Synchronization: Devices in MC-LAG must maintain accurate network state synchronization, ensuring that routing and forwarding information is consistent across all chassis.
  • Management and Monitoring: Constant monitoring of the MC-LAG is essential to identify possible failures, analyze performance and ensure that the network is operating within expected parameters.


Differences and Similarities in Relation to Other Technologies:

MC-LAG differs from other link aggregation technologies, such as LACP and VSS, in several aspects. Despite using LACP, when configured without MC-LAG, it is a protocol that allows the aggregation of links between two chassis, while MC-LAG aggregates links between multiple chassis. On the other hand, VSS is a Cisco-specific technology that virtualizes two chassis into a single logical system. Both technologies aim to increase availability and scalability, but each has its own distinct characteristics and requirements.

Typical Use Cases:

MC-LAG is widely used in network scenarios that require high availability and scalability. Some typical use cases include:

  • Data Centers: MC-LAG is used to ensure continuity of services in critical environments, where any downtime can result in significant losses.
  • Service Providers: MC-LAG is used in service provider networks to provide reliable connectivity to customers and handle traffic efficiently.
  • Large Business Environments: Companies with complex and distributed networks can benefit from MC-LAG to ensure service availability and facilitate network scaling as demand grows.


MC-LAG configuration on DmOS

Specifically in the context of DmOS version 9.2, MC-LAG is operationalized in Active/Standby mode. In this configuration, one of the PEs plays the active role, taking charge of the traffic, while the second PE remains on standby, acting as a contingency to ensure network continuity and reliability.

The LAG admin-key in PEs and CE must be the same. In the configuration below, lag-1 will be used. DmOS uses the admin-key value with the same value as the

Primeiramente iremos configurar as interfaces:

The lowest index lag-priority configuration will define what the active PE will be. Using the same lag-priority value in both PEs should be avoided.



MC-LAG, as a strategic solution in the telecommunications universe, emerges as a direct response to modern networking challenges, providing not only high availability, but also unparalleled efficiency and adaptive scalability. Its implementation, when carried out accurately and based on a clear understanding of its benefits and nuances, leads to a robust infrastructure. This infrastructure, in turn, is positioned to meet the growing demand for continuous, high-quality connectivity, making it a fundamental choice for organizations seeking excellence in their network operations.

At Datacom, we understand the importance of continuous training. Therefore, we offer both in-person training at our headquarters (subject to availability) and on our online platform, DATACOM EAD. In these trainings, participants have the opportunity to configure different topologies, learn best practices and rely on the expertise of our professionals.

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