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Difference Between LAG vs LACP

In the 1980s, Ethernet was developed to connect local devices in a region. It was called the Local Area Network. The purpose was to transmit and receive data from different people in the area. By connecting Ethernet devices using Ethernet switches, we can now connect over a larger Ethernet network.
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.

What Is LAG?

LAG – Link Aggregation Groups
To connect two switches, we use a cable to connect two physical ports (one in each of the switches) and configure them as a trunk. But a single trunk has bandwidth limitations. We can use stacking to obtain higher bandwidth, but stacking is mostly proprietary and supports a limited distance. In order to obtain high-bandwidth trunk lines between two switches (or two devices), we can use LAG – Link Aggregation Group.
LAG is a process of inter-connecting two switches with two or more links between them (or between a switch and a server), so that multiple links are combined into one bigger virtual link that can carry a higher (combined) bandwidth. All these multiple links participating in a Link Aggregation Group act like a single large (virtual) link.
 
If two switches support 1 GE ports, multiple ports from one switch can be connected to multiple ports in another switch to provide high-bandwidth connections (2 GE, 3 GE, etc) between the switches.
A practical situation to consider: If two switches are connected to each other with a bandwidth of 1 GE and the network administrator feels that it is insufficient, they can either buy another switch with 10 GE trunk support (hardware upgrade, more expensive) or just connect multiple ports between these two switches and configure them as a Link Aggregation Group. This approach is not only inexpensive (doesn’t require hardware upgrades), but also allows a granular upgrade of interconnect bandwidth between the two switches.
LAG is also used for increasing link reliability. Since multiple links connect two devices, even if one fails the other links keep carrying the information and the traffic on the failed link is also transferred to them. That way, loss of a single link between two switches doesn’t stop the communication between them. Multiple links participating in a LAG can also load-balance the traffic between them so that traffic is evenly distributed.
The number of links that can combine to form a larger link between two devices is generally restricted by the hardware vendor. LAG is a static protocol and needs to be configured individually for each pair of physical ports. LAG is a standard.

LAG Advantages

  • LAG is inexpensive. We can improve connectivity by increasing bandwidth, whereas it would have cost a lot if we had to install new cable runs.
  • LAG allows for the expansion of bandwidth that serves as a single link but is actually an aggregation of numerous links.
  • LAG balances the traffic load by dividing it among the physical links.
  • If one link is lost or broken, the other will not be broken. Networking is not delayed and the damage can be repaired until then.

What Is LACP?

LACP – Link Aggregation Control Protocol
LACP is similar to LAG, where multiple ports/links between two switches combine to provide higher bandwidth links between them. Additionally, ports that are LACP enabled can automatically configure themselves into trunk groups, without any manual configuration/intervention.
The main purpose of LACP is to automatically add/delete individual links to the aggregate bundle, while adding new links and also after recovering from link failures. LACP can monitor to verify if all the links are connected to the right group. Basically, LACP helps automate the configuration and maintenance of LAG’s.
LACP is a dynamic protocol. It is sufficient if multiple ports on various devices are LACP enabled, once. LACP is a standard and hence LACP can be implemented between multi-vendor switches. LACP should be enabled on the trunk ports initially in order for both the participating switches/devices that support the standard, to use it. If there are more links (between two devices) than what is supported by the vendor for LACP, the additional links are placed in stand-by mode and activated automatically when a link fails.

LAG vs LACP-LAG Implementation Scenario

Since LACP is only a protocol for Link Aggregation Group. Take 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.
Linking 4 1GE ports in parallel on 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 48 port PoE switch.

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.

Cisco LAG vs LACP

For example, let’s compare Cisco LAG vs LACP.
The main difference between Cisco LAG and LACP is that Cisco LAG is an instance for link aggregation, while LACP is the action that creates an instance of link aggregation. If we look at LAG as a process, LACP is the protocol that governs the process.
LACP is the monitoring unit that controls the operation of the LAG. Link Aggregation Control Protocol justifies its name being the protocol that allows LAG to function on its own. On the other hand, we can create a static link aggregation group without implementing any link aggregation control policy. Optionally, we can use LACP to protect the connection.

Comparison Table Between Cisco LAG and LACP

 
Parameters of comparison Cisco LAG LACP
Known as Link Aggregation Group. Link Aggregation Control Protocol.
Definition Cisco lag is a technique. LACP is a protocol that controls the technique.
Purpose Clubs multiple ports between two ethernet devices. Monitors the function of LAG.
Static mode LAG is required. During static mode, LACP is not required.
Dependency LAG can operate without LACP, that is it is independent. Dependent, i.e it is a protocol and you need some technique (like LAG) that you can use to start your control.
 

Conclusion

The key difference between LAG and LACP is that LAG is the link aggregation instance, whereas LACP is the action that monitors the link aggregation instance. If we think of LAG as a process, LACP is the protocol that governs the process. LAG is a combination of two devices with more than one link. With Link Aggregation Groups, we can combine multiple network interfaces into one intellectual interface which increases network speed. Apart from LAG, it is also known as Ethernet bonding, because it groups an Ethernet link between two Ethernet devices. LACP is the monitoring unit that controls the operation of the LAG. The Link Aggregation Control Protocol justifies its name by being the protocol that instantiates LAG by itself. On the other hand, we can create static link aggregation groups without applying any link aggregation control policies. Optionally, we can use LACP to secure a connection and enhance availability.
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.

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