What Is Link Aggregation Control Protocol In Networking And Communication

Link Aggregation Control Protocol

Link Aggregation Basics

In the process of networking, wired and wireless both are useful methods. However, wired methods are proven more effective than wireless. But while networking, it’s troublesome to manage many wires at once. To solve this problem, link aggregation plays a vital role. since it’s known to carry multiple ports collectively as a single channel. In other words, link aggregation combines multiple physical ports as one port, which makes it easy to carry out the task by the user. Also, it makes the process cost-effective.

Defined within IEEE 802.3ad, the Link Aggregation Control Protocol (LACP) is a standards-based method to control the bundling of several physical network links together to form a logical channel for increased bandwidth and redundancy purposes. LACP enables a network device to negotiate an automatic bundling of links by sending LACP packets to the peer. By sending specialized frames down links with the protocol enabled, LACP dynamically configures these peers and failover occurs automatically when a link fails.

Link Aggregation Control Protocol or LACP is one element of an IEEE specification (802.3ad) that provides guidance on the practice of link aggregation for data connections.

Importantly, LACP typically applies to strategies that bundle individual links of Ethernet connections, and not wireless transfers.

First, it provides redundant network activity. Suppose you have a single link, and that link fails. All of a sudden, you have a 100% lack of data connectivity. Your system just cuts off, it “goes dark.”

With link aggregation, on the other hand, you get multiple delivery paths, and the ability to do load-balancing across all of the available links. Now, using the same link for each related packet is still a best practice.

Making sure that all related data packets go through the same individual link solves potential problems with out-of-order packets, and link aggregation has to address this reality.

However, as you might imagine, the bundling of individual links leads to much more durable signal interfaces.

There’s also the promise of “graceful degradation” — in other words, failure occurs slowly, and gradually, not all at once.

Instead of “cutting off,” a signal might only initially suffer a small but of degradation, giving the end user or other stakeholders time to react and diagnose the problem and address it.

Various link aggregation configuration guidelines help to optimize how link aggregation protects network data and performance.

With that in mind, LACP promotes the formation of better logical virtual links or bundles that can be handled as one unified whole by an MAC client.

Generally, the bundling offers system designers and administrators new ways of addressing points of failure and recovery capabilities without going to greater extremes.

As part of Link Aggregation Control Protocol practices, engineers identify the aggregated interface, and confirm link status. The identifier value for the virtual local area network will also be included.

As noted by experts, it’s important that devices on both ends of the connection support link aggregation in the same ways, so “termination” may also be important.

Systems inherent in the LACP process can also help to handle the out-of-order packet problem: tools referred to as “scheduling algorithms” define packet-to-packet activity to keep things working well.

Although vendor systems provide for this protocol, some open source providers also accommodate the implementation of link aggregation with resources to help support this type of approach.

In general, LACP helps to standardize how link aggregation happens, for more durable Ethernet transmissions.

Structure of LACP:

Link aggregation applies to any three bottom layers of the OSI model. Here, power lines and wireless network devices, which combine multiple frequency bands, can be a good example of link aggregation at layer1 or the physical layer

In layer2 it usually happens between the switch ports, for instance, Ethernet frame in LAN or multi-link PPP in WAN, data link layer, or Ethernet MAC address, which can be either virtual or physical ports.

In the network layer or layer3, it can use the Round-robin scheduling. For aggregation at layer 3 of the OSI model, hash code computed from fields in the packet header, or combining both methods, can be used.

It can maintain the balance in network load across all links, regardless of the aggregation layer. However, it may not be used in some cases to avoid out-of-order delivery. In most cases, the failover is also included in this kind of method.

In the process, combining is possible only if either, the majority of interfaces are sharing the same IP address or the other way is when each interface has its address. Here, the first one may need both ends of a link to share the same aggregating procedure, but it is considerably better in terms of performance.

On the other hand, Load balancing divides the traffic across the interfaces based on the network socket or layer 4, besides, the channel bonding indicates a lower-level division of traffic between physical interfaces, either based on the per-packet or the data link.

Features of LACP:

  1. The maximum range of a valid number of ports is 1 to 8, which are used in the channel.
  2. To send LACP packets with multiple grouping, the MAC address 01:80:C2:00:00:02 is used.
  3. During the process of LACP detection, the LACP packets are sent every second, and also the keep-alive mechanism for link members can work faster by the 1sec. and slower by the 30sec. (which is set by default)
  4. The option of load-balancing mode is also available, which can be selected in some cases. But not necessarily at all.
  5. The LACP mode contains two main modes, active and passive. Active mode helps the LACP to run indefinitely. On the other hand, the passive mode can activate LACP only, once the LACP device is found. Which is also a default setting.

Standardization of the Link Aggregation:

The standardization of the link aggregation includes the two main standards of link aggregation control protocol.

1. The 802.3ad IEEE Link Aggregation:

The IEEE 802.3ad of Link aggregation makes it easy for the users to group Ethernet interfaces at the physical layer to create a single link-layer interface, often known as a LAG or bundle.

Sometimes the user needs more bandwidth in the network, which is not possible with a single Ethernet link. However, a high-speed Gigabit Ethernet link can be very expensive. On the other hand, using IEEE 802.3ad link aggregation can be a good solution. It can increase port density and bandwidth at a very less cost. Take an example, suppose there is a need for 450 Mbps of bandwidth for data transmission, but there is only a 100 Mbps Ethernet link available. In this kind of situation, it is more convenient to create a LAG bundle of Five 100 Mbps fast Ethernet links than to buy a single Ethernet link.

As for functionalities, the link aggregation provides protocols, and procedures, and manages the objects to allow one or more parallel instances of full-duplex links to be aggregated together, to form a Link Aggregation Group or LAG.

2. The 802.1AX:

The IEEE 802.1AX-2008 is an upgraded version of 802.3ad IEEE standard, which is usually used to bundle up the multiple network connections into the parallel full-duplex point-to-point link, which can be used as a single point link. this kind of link aggregation provides a higher availability and transmission speed than the conventional connection.

How to Configure LACP?

  1. First of all, enable the LACP, and then, configure the per-port specific LACP, either in Active mode or Passive mode. Usually, the range of group numbers goes from 0 to 7.
  2. In the second step, the user needs to set a timeout for the LACP session, which defines the amount of time that a port channel will wait for a LACPDU before terminating the LACP session. It can go 3sec shorter to 90sec longer.
  3. The third step is to set a priority value. It can be high or low accordingly. By default, it is 255, but the range can go higher to 1-65535.
  4. View the LACP configuration.

Here are screenshots for a better understanding of the process:

LACP Port Selection

LACP Port Selection


LACP Commands


  1. Increased bandwidth: The main advantage of the link aggregation control protocol is that it is capable of combining multiple links into one logical link. which helps increase the bandwidth of the network.
  2. Automatic occurrence of failover and failback: once the link failure occurs, the traffic under the failed link then automatically turned onto the other available links. Which makes it a reliable method for data transmission.
  3. Cost-effective method: link aggregation is a cost-effective method. It combines multiple links into one, which makes it less costly and reliable at the same time.
  4. Less drain on the network address pool: The whole aggregation process can be assigned one IP address. which makes it a less confusing and time-saving method.

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