LAG vs LACP: What’s the Difference?

In the field of Ethernet switch connection, link aggregation is a technology to combine multiple ports in parallel between different network switches. It functions to expand bandwidth cost-effectively and to provide redundancy in link failure. However, the umbrella term “link aggregation” is rather a broad terminology containing various conceptions: Link Aggregation Control Protocol, Link Aggregation Group, MLAG, 802.3ad, 802.1AX, etc. Among them the issue of LAG vs LACP confuses many people. Here we introduce LAG vs LACP in sequence and compare LAG vs LACP to illustrate their relationships and differences.

LAG vs LACP What is the Difference

LAG vs LACP: What Is LAG?

LAG (Link Aggregation Group) is an actual technique or instance for link aggregation. A Link Aggregation Group forms when we connect multiple ports in parallel between two switches and configure them as LAG. As thus LAG builds up multiple links between two switches, which expands bandwidth. Besides, it provides link-level redundancy in network failure and load-balance traffic. Even if one link fails, the remaining links between the two switches will still be running. They also take over those traffic supposed to traverse via the failed one, so data packet won’t get lost.

LAG vs LACP: What Is LACP?

LACP (Link Aggregation Control Protocol) is a control protocol to set up LAGs automatically. So you can choose to build a static LAG without LACP. Or you can choose to set up a dynamic LAG by using LACP. Simply put, LACP is not a link aggregation instance but a protocol for defining it. LACP enables LAG to transfer from static LAG to dynamic LAG, which allows information exchange of the link aggregation between the LAG component network switches. The information is delivered as packet in Link Aggregation Control Protocol Data Units (LACPDUs). And each port on both switches can be configured to be active or passive via the control protocol to be either preferential to transfer LACPDUs or not.

LAG Implementation Scenario

Since LACP is only a protocol for Link Aggregation Group. We’ll omit the LAG vs LACP differentiation to see LAG implementation scenario by FS.COM. Taking the LAG between two gigabit PoE network switches and another 10GbE fiber switch as example. While simply connecting one port on each gigabit PoE switch with one cable, we get 1GE bandwidth. However, when you double link, triple link or higher multiples, the bandwidth will become 2GE, 3GE and so on.

Further, to uplink a backbone core switch, we can use 4 fiber patch cables with corresponding modules to link the 48 port gigabit PoE switch 10GE SFP+ ports and the 10GbE fiber optic switch. Then the uplink bandwidth on the S1600-48T4S expands to 40GE. In the case two LAGs form on the 48 port PoE switch. The link upper limit to form a LAG and the number of LAGs between two switches vary from vendor and switch models.

LAG vs LACP link aggregation implement scenario by fs PoE switch and fiber switch

Figure 1: Linking 4 1GE ports in parallel on FS 48 port PoE switch and 24 port PoE switch to set up a LAG, which boosts bandwidth from 1000Mbps to 4 × 1000Mbps. In this photo two LAGs have been implemented on the FS 48 port PoE switch.

LAG vs LACP : Link Aggregation Advantages to Expand Bandwidth

Whether LAG deploying Link Aggregation Control Protocol or not, it requires no expensive hardware upgrade. Therefore Link Aggregation Group provides a cost-effective solution for bandwidth expansion. Stacking switch is indeed an advanced method to obtain higher bandwidth. However, it is restricted to stackable switch and does not support separate placing. To buy a higher speed switch like a 10GbE switch is also an direct and effective solution. But for ordinary users this hardware upgrade is over budget.

LAG vs LACP: What’s the Difference?

  • Link Aggregation Group is a practical instance of link aggregation whereas LACP is a protocol for auto-configuring and maintaining LAG.
  • LAG without Link Aggregation Control Protocol is a static configuration, in which each pair of ports in a LAG require manual configuration respectively. However, LACP enabled ports are dynamic configuration, which enable to auto-configure into trunk groups when building LAG.
  • When talking about LAG vs LACP, one usually refer to static LAG without LACP vs dynamic LAG with LACP. Generally speaking, dynamic LAG configuration owns advantages over static LAG configuration for automatic failover occur and mutual dynamic configuration. In static link aggregation, LAG cannot detach configuration or cabling errors so as to cause unnecessary network troubles.

Conclusion

LAG vs LACP issue is put forward for the confusing conception between them. LAG is an actual instance for link aggregation. LACP is a control protocol to enable LAG automatically configure network switch ports, detach link failure and activate failover. So LAG encompasses both static LAG configuration and dynamic LAG configuration on the basis of whether employing optional Link Aggregation Control Protocol or not. As a whole, Link Aggregation Group is a cost-effective way to expand bandwidth over switch stacking and other hardware upgrade methods. For minimizing network link failure, LACP enabled dynamic LAG configuration over static LAG is a much better solution to go.

Understanding Link Aggregation and LACP

Link aggregation, as its name indicates, is the approach to combine multiple parallel physical network links into a single logical link to increase bandwidth and create resilient and redundant links. It enables us to enhance the capacity and availability of the connections between devices using Fast Ethernet and Gigabit Ethernet technology. LACP, known as link aggregation control protocol, is the standard protocol supported by IEEE 802.3ad to configure link aggregation. This article will shed some lights on link aggregation and LACP technology.

link aggregation

What Is Link Aggregation and LACP, Why Use them?

Link aggregation allows one to combine multiple network connections (same data rate, duplex capability, etc) in parallel to increase throughput beyond what a single connection could sustain, and to provide redundancy in case one link goes down. Besides, link aggregation load balance enables the processing and communications activity to be distributed across several links in a trunk, thus not overwhelming a single link. Moreover, improvements within the link are obtained using existing hardware, so you don’t have to upgrade to higher-capacity link technology. This technology is not just for core switching equipment such as link aggregation switch. Network interface cards (NICs) can also sometimes be trunked together to form network links beyond the speed of any one single NIC.

link aggregation control protocol

LACP is a vendor independent standard protocol for link aggregation. LACP links need to be manually configured on the physical network switch, to allow both links to appear as one logical aggregated link. LACP provides automatic determination, configuration, and monitoring member links. When LACP is enabled, a local LAG (link aggregation group) cannot transmit packets unless a LAG with LACP is also configured on the remote end of the link. A typical LAG deployment includes aggregate trunk links between an access switch and a distribution switch or customer edge (CE) device.

How Does LACP Work?

In a LACP enabled link, the firewall is capable of using LACP to detect the physical interfaces between itself and a connected device and manage those interfaces as a single virtual interface (aggregate group) – which increases the bandwidth between devices. Enabling LACP provides redundancy within the group: the protocol can detect interface failures automatically and performs failover to standby interfaces. Without LACP, you must spend more time manually identify interface failures occurring within the channel.

LACP protocol benefit

LACP for Gigabit Interface Configuration

By transmitting LACP packets between ports, LACP supports the automatic creation of Gigabit Ethernet port channel. It is capable of dynamically grouping port and informing the other ports. As LACP successfully identifies matched Ethernet links, it facilitates grouping the links into a Gigabit Ethernet port channel. Then it begins to change LACP packers between ports in either the two modes:

  • Active—Places a port into an active negotiating state, in which the port initiates negotiations with remote ports by sending LACP packets.
  • Passive—Places a port into a passive negotiating state, in which the port responds to LACP packets it receives but does not initiate LACP negotiation. In this mode, the port channel group attaches the interface to the bundle.

Both modes allow LACP to negotiate between ports to determine if they can form a port channel based on criteria such as port speed and trunking state. Here are some important parameters to use during configuration of the link aggregation.

LACP System Priority: This is configured per router. It is used with MAC address to create LACP System ID.

LACP System ID = LACP System Priority + MAC Address

LACP Port Priority: It is configured per port. It is used to form Port Identifier with Port Number.

LACP Port Identifier = LACP Port Priority + Port Number

It is also used to determine which port should be in standby mode during an hardware limitation.

LACP Administrative Key: It is automatically calculated equal to the channel group identification number on each LACP configured port. It defines the ability of a port to aggregate with other ports, the aggregation ability is determined by, port characteristics and configuration restrictions.

LACP Max-bundle: It is the number of bundled ports in a bundle. As I mentioned below it is maximum 8. But in some platforms it can be 4.

If all the compatible ports cannot be aggregated by LACP, then the remaining ones can act as standby ports. When there is a failure occurs in one of the bundled ports, the standby ports become active one by one.

Conclusion

Link aggregation is the efforts made to set up parallel network structures to provide redundancy, or to improve performance, which increases bandwidth, provides graceful degradation as failure occurs, and enhances availability. LACP facilitate the configuration of link aggregation with automatic determination, configuration, and monitoring. Hope this article could help understanding link aggregation and LACP.