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What is the difference between LACP & PAGP?

When it comes to network design, there are usually multiple avenues to arrive at the same result. Any number of arrays can ultimately provide the network coverage you need, and there are always different protocols for managing and controlling networks.

A common technique that is used to increase throughput for Ethernet systems is link aggregation. This technique can increase effective transmission speeds while making a network more robust. There are a few ways to aggregate links, and two of the leading protocols are LACP and PAGP.

What Is Link Aggregation?

Link aggregation is the main concept that LACP and PAGP have in common. It can be achieved in a few different ways, but ultimately, link aggregation is a way to bundle connection links under a single logical framework. In other words, all of the links in the bundle are managed together like a single unit.

Aggregation works to improve overall performance by automating the task of balancing connections across the different links. While doing this, the aggregation logic builds redundancy. If one link in a bundle fails, the system can automatically reroute traffic through working links.

Perhaps most importantly, link aggregation allows for more simultaneous data transmission. Since a bundle has multiple links, packets can go across multiple inks in the bundle at the same time for better overall effective speeds.

What is LACP?

LACP, or Link Aggregation Control Protocol, is one of the most-used methods for aggregating Ethernet links. It is defined in the IEEE 802.3ad standard. As an aggregation protocol, it bundles the physical Ethernet ports in a system into a single logical channel, gaining the benefits listed in the previous section.

As an IEEE 802.3ad standard, LACP is supported by a range of vendors, making it a roughly universal method of aggregating links. One of the primary advantages of using LACP is that it supports cross-stack aggregation. Even if you use multiple vendors, as long as they all support LACP, you can bundle them as you see fit.

What is PAGP?

PAGP stands for Port Aggregation Protocol. Off the bat, the primary distinction of PAGP is that it is a Cisco proprietary protocol. It still works to automate dynamic grouping of ports into a logical link, aggregating Ethernet ports, but it is an entirely distinct protocol.

Because it is proprietary, it only works with Cisco equipment (or Cisco-supported equipment). This limitation comes with an additional built-in function. PAGP equipment can automatically check connected systems to see which are PAGP compatible. The system aggregates according to those automated checks. This makes PAGP setup a bit simpler and easier to manage, provided you have enough supported equipment for the bundles you want to create.

The Primary Differences Between Protocols

Ultimately, LACP and PAGP are achieving the same results. They are working in similar fashions to aggregate network links, but the major differences matter a lot in network design. The primary difference is the proprietary nature of PAGP, but that’s not the whole story.

For instance, LACP provides a passive and active mode. The default mode is active, while the passive setting offers a different approach. When passive, the bundle can receive packets, but it won’t initiate LACP negotiation.

PAGP has an auto mode and desirable mode which ultimately serve these same roles. The auto mode functions passively while the desirable mode is active.

In every way, the protocols take slightly different approaches to link aggregation. While they provide comparable performance, the differences in these approaches change network design from an engineering perspective.

Which Should Your Network Use?

How do you make the important decision between LACP and PAGP? Your existing equipment can help you decide. If you’re already heavily invested in Cisco equipment, PAGP could prove to be the more cost-effective option. It can also simplify setup and save on labor costs.

If your vendors are more diverse, LACP will almost certainly prove cheaper and better from a design perspective.

Additional Learning Center Resources