What is MLAG – Saikat Infotech

MLAG,VSS,VPC

Multi-Chassis EtherChannel (MLAG) is a network design concept where two (or more) physical network devices (usually switches) act as a single logical entity for the purpose of creating a high-availability and load-balanced network link. This method is commonly used in data centers and large enterprise networks to provide redundancy and increase bandwidth.

In an EtherChannel, multiple physical links between switches or between a switch and a server are bundled together to form a single logical connection. The goal of MLAG is to allow these aggregated links to appear as a single logical link to the connected devices while still maintaining the advantages of redundancy, fault tolerance, and increased throughput.

Key Concepts of MLAG:

Redundancy: MLAG ensures that if one physical link or switch fails, the other one can take over, providing uninterrupted network services.
Load Balancing: By combining multiple links, MLAG enables better distribution of network traffic, optimizing the use of available bandwidth.
Multiple Chassis: In MLAG, two switches are involved. One acts as the primary and the other as the secondary switch. They appear as a single device to end devices or upstream switches.
Loop Prevention: Protocols like the Spanning Tree Protocol (STP) or MLAG-specific protocols help in preventing network loops while allowing the redundancy and increased bandwidth benefits of MLAG.

How MLAG Works:

EtherChannel Aggregation: Just like standard EtherChannel, MLAG combines multiple physical links into one logical connection.
Active/Standby Setup: The two switches (usually from the same vendor) are configured to work together. One switch typically handles active traffic, while the other remains in standby mode.
Synchronization: The two switches are synchronized in terms of the state of the EtherChannel, making sure that one switch can take over in case the other fails without losing traffic.
Control Plane and Data Plane: The control plane is responsible for managing the network information, while the data plane is where the traffic flows. MLAG ensures that the control plane is synchronized between switches, while the data plane can operate with full bandwidth redundancy.

Benefits of MLAG:

High Availability: If one switch fails, the other can still forward traffic without interruption, ensuring network uptime.
Better Utilization of Links: MLAG allows you to maximize the use of available bandwidth between devices by aggregating multiple links.
Scalability: More links can be added to increase capacity, making the network scalable to meet increasing demand.

Key Requirements for MLAG:

Switch Compatibility: Both switches in the MLAG pair must support MLAG. Many enterprise-grade switches, like those from Cisco (e.g., Nexus 7000) and Arista, offer MLAG functionality.
Inter-Switch Communication: The switches need a direct link between each other (referred to as the MLAG Peer Link) to synchronize their configurations and state.
EtherChannel Configuration: The physical ports that will be part of the MLAG configuration must be configured to work as an EtherChannel (using protocols like LACP or PAgP).
Layer 2 Domain: MLAG is typically used in Layer 2 environments, but it can also extend to Layer 3 in some cases.

Example Use Case:

In a data center, MLAG could be used to connect two aggregation switches to multiple server racks. The servers would each connect to both aggregation switches through two separate physical links (configured as part of an EtherChannel). If one of the aggregation switches fails, the traffic can continue to flow through the other switch, ensuring network reliability.

Would you like more details on how MLAG works in practice with a specific vendor’s equipment?

In the era of digital transformation, data centers have become the cornerstone of enterprise operations, enabling everything from cloud computing to big data analytics. As businesses expand and their network traffic grows exponentially, ensuring high availability, scalability, and operational efficiency within data centers is more critical than ever. Multi-Chassis Link Aggregation Group (MLAG) has emerged as a pivotal technology to address these needs, providing robust solutions for network redundancy, load balancing, and simplified management. This article will delve into the fundamental concepts of MLAG, explore its diverse applications, and discuss its crucial role in modern data center network design.

MLAG Overview

Multi-Chassis Link Aggregation Group (MLAG) is a sophisticated networking technology that enhances traditional Link Aggregation Group (LAG) by allowing link aggregation across multiple switches. This architecture significantly improves network performance and reliability by providing enhanced redundancy and load balancing.

MLAG functions by presenting two or more physical switches as a single logical switch to connected devices. This is made possible through synchronization protocols and control mechanisms that ensure coordinated operation of the switches. Key components of MLAG include:

Control Plane Synchronization: Ensures that MLAG peers maintain consistent forwarding states and configurations.
Data Plane Operations: Facilitates efficient data transfer across aggregated links, balancing the load and ensuring seamless failover capabilities.
Keep Alive Mechanisms: Monitors the health of MLAG peers, detecting failures and triggering appropriate responses to maintain network stability.

Is MLAG the Same as LACP?

While MLAG (Multi-Chassis Link Aggregation Group) and LACP (Link Aggregation Control Protocol) both aim to enhance network performance and reliability through link aggregation, they are not the same. They differ in their scope, operation, and use cases. Here’s a comparison to highlight their distinctions:

Scope and Operation

MLAG:

Scope: Operates across multiple switches, treating them as a single logical switch to connected devices.
Redundancy: Provides high redundancy by allowing failover between switches.
Load Balancing: Distributes traffic across multiple switches.
Management Complexity: Requires more complex configuration and synchronization between multiple switches.
Scalability: More scalable for large networks, accommodating growing demands with multiple switches.

LACP:

Scope: Operates within a single switch, bundling multiple physical links into a single logical link.
Redundancy: Provides redundancy within a single switch, allowing traffic rerouting if a link fails.
Load Balancing: Distributes traffic across multiple links within the same switch.
Management Complexity: Simpler to configure and manage due to its operation within a single switch and adherence to the IEEE 802.3ad standard.
Scalability: Limited to the link aggregation capabilities of a single switch, less scalable for extensive networks.

Key Differences

Operation: MLAG spans multiple switches, while LACP is confined to a single switch.
Redundancy and Failover: MLAG offers switch-level redundancy, whereas LACP provides link-level redundancy within one switch.
Complexity: MLAG involves more complex setup and synchronization, while LACP is easier to implement and manage due to its standardization.
Use Cases: MLAG is suitable for large, scalable, and highly available network environments. LACP is ideal for simpler setups requiring link aggregation within a single switch.

Summary Table

Feature	MLAG	LACP
Scope of Operation	Multiple switches	Single switch
Redundancy	High (failover between switches)	Moderate (failover within switch)
Load Balancing	Across multiple switches	Across multiple links in one switch
Management Complexity	Higher (involves multiple switches)	Lower (standardized protocol, single switch)
Scalability	High (suitable for larger, scalable networks)	Lower (limited to single switch)
Protocol Standards	Vendor-specific implementations	IEEE 802.3ad standard
Failover Mechanism	Switch-level failover	Link-level failover

What is MLAG Used for?

Spine-Leaf Architecture

In spine-leaf network topologies, MLAG is used to connect leaf switches to spine switches. This architecture ensures that traffic between any two devices in the data center can traverse multiple paths, enhancing fault tolerance and load distribution.

High Throughput: Supports low-latency, high-throughput connections essential for data-intensive applications.
Resilience: Multiple paths between devices improve fault tolerance and reliability.

Server Connectivity

MLAG is often used to dual-home servers to multiple switches, providing redundancy and higher aggregate bandwidth. This configuration is particularly beneficial for critical servers hosting applications that require high availability and consistent performance.

Dual-Homing: Ensures servers remain connected even if one switch fails.
Increased Bandwidth: Aggregates links to provide higher bandwidth to servers.

Storage Networks

In storage area networks (SANs), MLAG connects storage devices to multiple switches, ensuring that data access is not disrupted in case of a switch failure. This setup is vital for maintaining the integrity and availability of storage resources.

Data Integrity: Continuous access to storage devices ensures data integrity.
Availability: Maintains high availability of storage resources.

Disaster Recovery and Business Continuity

MLAG supports robust disaster recovery and business continuity solutions by providing geographically dispersed redundancy. By extending MLAG configurations across data centers in different locations, businesses can ensure that their critical applications remain operational even in the event of a site-level failure.

Geographic Redundancy: Ensures network resilience across different geographic locations.
Operational Continuity: Maintains critical services and applications during disasters.

MLAG vs. Stacking vs. LACP
Link aggregation and stacking are common approaches to bundle multiple network connections in one logical link. Compared to conventional connections, these methods are best described as scalable solutions that can provide higher availability, higher reliability and higher bandwidth. MLAG vs. stacking vs. LACP is often asked to define the differences, so this article intends to give an informed explanation of MLAG, LACP, stacking, and the different application scenarios.

Understanding MLAG, LACP, and Stacking
MLAG (Multi-chassis Link Aggregation Group): a non-standard protocol, that implements link aggregation among multiple devices. The devices at both ends of the MLAG send MLAG negotiation packets through the peer-link. The main purpose of MLAG is to deliver system-level redundancy in the event one of the chassis fails.

LACP (Link Aggregation Control Protocol): a subcomponent of IEEE 802.3ad standard, provides a method to control the bundling of several physical ports together to form a single logical channel. LACP allows a network device to negotiate an automatic bundling of links by sending LACP packets to the peer. For more basics, Understanding Link Aggregation Control Protocol will give you the answer.

Stacking: a technology that enables multiple stacking-capable switches to function as a single logical switch. Stack link is connected by stacking cables to form a stack that connects all the switches in a specific topology. The stacking topology also defines the resiliency of the stacked solution. You can have typically different kinds of cabling options, depending on the switch vendor and models.

MLAG vs. Stacking: Which Approach Is Better?

Reliability

MLAG: MLAG has higher reliability because its control plane is independent, which isolates the fault domain.

Stacking: Stacking has average reliability as its control plane is centralized, which may lead to faults spreading across member devices.

Scalability

MLAG: MLAG has strong scalability as it is not limited by the capacity of a single device.

Stacking: Stacking has moderate scalability as its control plane capacity is limited by the main device.

Impact on business

MLAG: During upgrades, there is minimal interruption to the business. During expansions, the existing network architecture remains unchanged, and there is no impact on existing operations.

Stacking: During upgrades, there is an interruption of approximately 20 seconds to 1 minute to the business. During expansions with three or more devices, it is necessary to modify the existing network architecture or restart devices, which affects existing operations.

Network design

MLAG: MLAG has a more complex design with a logical dual-node setup.

Stacking: Stacking has a simpler design with a logical single-node setup.

Configuration

MLAG: MLAG has a more complex configuration with independent configurations for multiple devices.

Stacking: Stacking has a simpler design with a logical single-node setup.

In conclusion, stacking has the advantages of simpler configuration and design, but lower flexibility and reliability compared to MLAG. Stacking can add more ports and quickly increase network capacity. Its main advantage is the ease of management. MLAG, although more complex in configuration, offers stronger reliability due to its decoupled control plane and higher network flexibility. Additionally, MLAG also has a stronger impact on business as it can achieve almost no interruption during upgrades or expansions.

The decision to use stacking or MLAG is a matter of weighing up the pros and cons of the option and understanding your network architecture. For more

information: MLAG vs. Stacking: What Is Your Option?

MLAG vs. LACP: Similarities and Differences

Similarities

MLAG and LACP are very similar and accomplish the same goal. They are link aggregation methods of aggregating multiple network connections in parallel to increase throughput and provide redundancy in case one of the links fails.

Differences

LACP provides enhanced functionality for link aggregation groups (LAGs) by automating configuration and maintenance. LACP-enabled ports automatically form trunk groups without manual configuration. When a member link stops sending LACPDUs, it is removed from the LAG to minimize packet loss. If both devices support LACP, it is recommended over static LAG, but LAG configuration is still required on each device.

LACP can be implemented between multi-vendor switches.

The implementation of MLAG varies by vendor, all of which are proprietary.

Stacking vs. LACP: What Is the Difference?

LACP cannot bundle links across multiple switches. It can only bundle links within a single ethernet switch for increased bandwidth and redundancy. The primary purpose is to improve link-level reliability. To establish an aggregated connection between switches A, B, and C, you must enable LACP on specific ports on each switch and make physical connections.

Stacking technology allows for bundling multiple switches to act as a single logical switch, to increase equipment-level reliability. Those switches are directly connected by stacking cable for stack link.