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MLAG vs. Stacking vs. LACP

March 6, 2021

Link aggregation and stacking are commom approaches to bundle multiple network connections in one logical link. Compare to conventional connection, these methods are best described as scalable solutions that can provide higher avaliability, higher relaibility 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, 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.

Switch Stacking is a technology that enables multiple stacking-capable switches to function as a single logical switch. Stack link is connected by stacking cable to form a stack that connect all the switches in a specific topology. The stacking topology also define the resiliency of the stacked solution, you can have typically different kind of cabling options, depending on the switch vendor and models. For more information: Switch Stacking Explained: Basis, Configuration & FAQs.

MLAG vs. Stacking: Which Approach Is Better?

For many administrators, the primary driver for using stacking is ease of management. The major purpose of stacking is to add an increased number of ports while quickly increasing the capacity of a network. It would seem to makes sense to use switch stacking at the edge where the control plane services are not required for the full functioning of the network. If simplicity is required and bandwidth distribution is not a concern, stacking approach is recommended. Stacakable switches provide a more economical option with high scalability and flexibility, especially in campus environments.

MLAG can be configured at the ToR level or on the leafs, that provides high availability for servers or switches without sacrificing the number of links due to spanning tree (STP) implications. Control planes are independent and fault domains are isolated, so it is better control of traffic distribution across links. Traffic is more evenly distributed to each of the switches through MLAG. When high reliability and the service interruption time during software upgrade are required, but the increased maintenance complexity can be accepted, the decision could be MLAG.

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: When to Use LACP?

MLAG and LACP are very similar and accomplish the same goal. They are link aggregation methods of aggregating multiple network connections in parallel in order to increase throughput and provide redundancy in case one of the links fail. However, LACP provides additional functionality for link aggregation groups (LAGs). The ports that are LACP enabled can automatically configure themselves into trunk groups, without any manual configuration. Hence, LACP helps automate the configuration and maintenance of LAGs. When one member link stops sending LACPDUs, it is removed from the LAG. This helps to minimize packet loss. When both devices are LACP-supported, it is recommended to use LACP instead of static LAG. Notably, you still need to configure the LAG on each device.

It should be added that, LACP can be implemented between multi-vendor switches. But the implementation of MLAG varies by vendors, all of which are proprietary.

Stacking vs. LACP: What Is the Difference?

LACP itself doesn't provide the ability to bundle across multiple switches. It bundles across multiple ports on a single ethernet switch (aggregating the links of forwarding services) for improved link bandwidth and redundancy. The main porupose is to increase link-level reliability. However, stacking techonology allows for bundling multiple switches to act as a single logical switch, for the purpose of increasing equipment-level reliability. Those swicth are directly connected by stacking cable for stack link.

LACP link aggregation only need to enable LACP on the port, that can realize the automatic aggregation function. For example, switch A needs to establish an aggregated connection of two links with switches B and C. You only need to enable LACP on four ports on Switch A, and enable LACP on two ports on B and C respectively, and then make physical connections. That is, it is not necessary to specify which two interfaces of switch A correspond to switch B and which two interfaces correspond to switch C.

FAQ

Can I Use LACP ports to create the flexible switch stack? Can I configure stacking and LACP at the same time?

Stacking ports don't use LACP, they use their own stacking protocol. You need two ports on each switch to be configured for stacking. The ports between the switches should be configured as a ring to send packets. Once the switches are stacked, you can use LACP across the switches in the stack to other things.

Is it necessary to configure the LACP function after the switches are stacked?

That depends on the customer need. If customers want to increase the link reliability and bandwidth of the downlink, they can use the LACP link aggregation; if the customer is only for the convenience of management, then they do not configure.

Can the MLAG function be used for stacking? Is MLAG an Alternative to Stackable Switches?

It's ok. MLAG can expand port capacity beyond the limitation of switch stacking - simply adding another switch East or West by creating another MLAG to another switch. Using MLAG, each switch is independently able for forwarding traffic without passing to a master switch. The number of switches can be stacked is limited, and the added switch needs to not only be from the same vendor as the other members of the stack but the same model, software version, and license pack as well.

A switch supports stacking but does not support MLAG. Which scenorio is applicable?

When the port density of a system is insufficient for an increased number of users, you can add new member switches to the stack to increase ports. The configuration and design of stacking is simpler. Virtualizing two devices into a logical device can achieve functions similar to MLAG. The downstream device is connected to two switches separately, and LACP is configured, which can achieve the effect of redundancy, and there will be no loops.

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