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What is Link Aggregation & Link Aggregation Control Protocol?

What is Link Aggregation & Link Aggregation Control Protocol?

Network demands are always changing. You might have a perfect setup today, but tomorrow, something in your network is going to need more resources.

When that happens, you have to weigh the costs of upgrades, and when only one device really needs the boost, it’s hard to justify the cost of a major equipment overhaul.

There’s a perfect solution for these cases: link aggregation.

Link Aggregation Explained

The concept behind link aggregation (LAG) is rather simple. You can combine multiple Ethernet connections into a single logical link. In other words, you use two or more Ethernet ports to support a single connection.

This concept goes by many names, some of which include bonding, teaming, and trunking. Names aside, the point is to connect two devices with more overall Ethernet power.

Two of the most common uses of link aggregation connect one switch to another switch or a server to a switch. The aggregation increases the bandwidth across that single logical connection.

Benefits of Link Aggregation

Combining two connections into a single link sounds like it could get complicated. Why go through all of the trouble?

Well, aggregation comes with some powerful benefits. As mentioned before, doubling the Ethernet power in a connection increases the bandwidth. At the same time, the doubled resources are much more reliable and boost availability. Also, when you increase resources, you increase your ability to load balance, improving efficiency along the way.

On top of all of that, link aggregation can save a lot of money. If you need to improve the capacity of a single connection, you can aggregate links, or you can upgrade the connection type. Upgrading from Ethernet to something more powerful usually involves fiber optics, and that can be an expensive change. If you don’t need to remake your whole network infrastructure, link aggregation provides an extremely cost-effective solution.

Types of Link Aggregation

While link aggregation is simple in concept, there are multiple ways to go about it. To keep things simple, we can break aggregation into two categories: static and dynamic. Each offers its own benefits and shines in different use cases.

Static

Static aggregation requires an administrator to configure the ports assigned to the LAG. This means that LACP is disabled (more on that later), so you cannot use automated port management in a static LAG. The assigned ports in the LAG are always active, which means it is not affected by peer ports.

There are a few advantages to choosing the static option. The first is that it is more port-efficient. Dynamic arrangements can use up more port space for a single connection. Beyond that, static LAGs are directly controlled, more predictable, and often easier to troubleshoot.

Dynamic

Despite those advantages, dynamic LAGs are popular, and for good reasons. Dynamic LAGs utilize LACP. This is a standardized protocol that is explained in detail in the next section. The important thing here is that LACP handles port assignments for you.

A dynamic LAG requires a group of candidate ports that you can assign to the link. Most of those ports will remain on standby, and the LACP will determine which ports are active at any given time.

There are two clear advantages to choosing this method. First, it requires a lot less direct involvement from an administrator. Since LACP does the heavy lifting, you can save a lot of manpower on configuration.

Second, LACP creates standby ports. This creates redundancy that can keep the LAG functional even in the event of port failure.

Link Aggregation Control Protocol

We can’t do this discussion justice without getting into Link Aggregation Control Protocol (LACP). As you read above, link aggregation protocol automates port selection in a dynamic LAG.

More specifically, LACP is an IEEE standard designed specifically to reduce the amount of work necessary in creating and maintaining link aggregation connections. The official standard is 802.3ad, and any two devices that are LACP compatible can connect with a dynamic LAG.

Link aggregation is a powerful tool that enables you to boost connectivity between two nodes in a network. With static and dynamic aggregation options, you can optimize a LAG as you see fit.

Additional Learning Center Resources