What is LACP (Link Aggregation Control Protocol)? | Features, Modes, and Working Principle

LACP (Link Aggregation Control Protocol) allows port grouping to convert many physical ports of a switch in the network to a single logical channel. Additionally, the IEEE (802.3ad) document defines this protocol.

What is LACP (Link Aggregation Control Protocol)?

What is the LACP Protocol, and How It Works?

The LACP protocol initiates negotiations on an automatic group. It does this by forwarding the packets of a switch to other switches. In this case, the working logic is like the EtherChannel developed by Cisco and PAgP.

Since IEEE standardizes this protocol, devices from many brands on the local network can easily configure it. Furthermore, this promotes interoperability and compatibility.

Users can use it with the EtherChannel structure. Additionally, Cisco-branded network devices fully support this protocol. As a result, it ensures seamless network integration.

The IEEE 802.3ad document initially defined LACP. As networks grew and integrated other brands’ devices into local networks, they introduced the IEEE 802.1AX standard.

LACP and PAgP have similar working structures. Additionally, LACP detects settings on both devices and creates a compatible EtherChannel system.

Features of LACP Protocol

LACP standard has the following features;

  • The IEEE 802.3ad document defines it.
  • It converts many physical ports between devices into a single logical port.
  • It creates a connection by making automatic calls between the devices.
  • Because the IEEE defines it as a global protocol, many brand devices support it.
  • It ensures the consistency of the ports on the device against possible errors.
  • If you configure any of the ports in this group, this group will change the settings of the other physical ports. So, the configuration becomes consistent across all the ports in the group.
  • Each device transmits packets through the group that created the channel.
  • The lowest priority switch in the network determines the physical ports assigned to the current channel. Subsequently, these assigned ports form the track with the appropriate configuration.
  • It considers ports with higher priority in the group as active.
  • It can assign 16 physical ports to the logical channel. But, it configures eight redundant ports to provide backup in case of failures.

Modes of Link Aggregation Control Protocol

On

The “On” mode forces the Switch to create a channel without including its port in LACP. But, the configured interfaces do not change LACP packets.

Active

The “Active” mode sets one Switch port to an active negotiation state. As a result, it sends packets to start negotiations with other ports.

Passive

The “Passive” mode sets a port of the Switch to passive handshake. So, this port responds to the packets it receives but does not start packet negotiation.

What is the Working Principle of the LACP Protocol?

As with the PAgP protocol, the configurations must be identical on both devices. Thus, an EtherChannel connection can occur in this protocol.

In open mode, it unconditionally generates and repeats the EtherChannel configuration. Thus, it doesn’t run PAgP or LACP dynamically. So, it doesn’t dynamically run PAgP or LACP.

The link aggregation control protocol supports eight active and eight redundant connection structures. It also activates the standby connection when an active link fails to ensure continuous network traffic.

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