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This article mainly introduces the ways of link aggregation in load balancing, which can be used for reference. I hope you can learn a lot after reading this article. Let's take a look at it.

The three ways of link aggregation in load balancing are manual load sharing mode link aggregation, static LACP mode link aggregation and dynamic LACP mode link aggregation. Manual load sharing mode is one of the most basic link aggregation methods.

This article operating environment: windows10 system, thinkpad T480 computer.

Three modes of link aggregation in load balancing:

Manual load sharing mode link aggregation

1. Overview of manual aggregation

Manual load sharing mode is one of the most basic link aggregation methods. In this mode, the establishment of Eth-Trunk interface and the joining of member interfaces are completely manually configured without the participation of link aggregation control protocol. In this mode, all member interfaces (selected) participate in data forwarding and share the load flow, so it is called manual load sharing mode. The LACP protocol of the manual trunk port is turned off, and the user is prohibited from enabling the LACP protocol of the manual trunk port.

2. Port status in manual aggregation group

In a manual aggregation group, the port may be in two states: Selected or Standby. The port with the lowest port number in the Selected state is the primary port of the aggregation group, and the other ports in the Selected state are member ports of the aggregation group.

Due to the limit of the maximum number of ports in the aggregation group that the device can support, if the number of ports in the Selected state exceeds the maximum number of ports in the aggregation group that the device can support, the system will select some ports as Selected ports and others as Standby ports according to the port number from smallest to largest.

3. Requirements of port configuration for manual aggregation

In general, manual aggregation does not limit the port rate and duplex mode before aggregation. However, the system will make special treatment for the following cases: for ports that are initially in the DOWN state, there is no limit on the rate and duplex mode of the ports during trunking.

For ports that were once in UP state and negotiated or forced to specify port rate and duplex mode, while ports currently in DOWN state are required to have the same rate and duplex mode when trunking; for an aggregation group, when the rate and duplex mode of a port in the aggregation group change, the system does not disaggregate, and the ports in the aggregation group are in normal working state. However, if the rate of the primary port decreases and the duplex mode changes, packet loss may occur in the forwarding of that port.

LACP protocol link aggregation

There are two types of LACP (Link Aggregation Control Protocol) link aggregation:

1) static LACP mode link aggregation

A) introduction to static LACP mode link aggregation

In static LACP mode, the establishment of Eth-Trunk interface and the addition of member interface are all done by manual configuration. However, different from manual load sharing mode link aggregation, LACP protocol messages participate in the selection of active interfaces in this mode. In other words, when a group of interfaces are added to the Eth-Trunk interface, which interfaces of these member interfaces are active interfaces and which interfaces are inactive interfaces need to be determined by the negotiation of LACP protocol messages.

The LACP protocol of the static trunking port is in the enabled state. When a static aggregation group is deleted, its member ports will form one or more dynamic LACP trunks and keep LACP enabled. The LACP protocol that prevents users from shutting down static trunking ports.

B) Port status in the static aggregation group

In a static aggregation group, the port may be in two states: Selected or Standby. Both Selected port and Standby port can send and receive LACP protocol, but Standby port cannot forward user messages.

2) Link aggregation in dynamic LACP mode

A) introduction to dynamic LACP mode link aggregation

In dynamic LACP mode, the establishment of Eth-Trunk interface, the joining of member interface and the selection of active interface are completed by LACP protocol through negotiation. This means that there is no need to create Eth-Trunk interfaces or specify which interfaces are members of the aggregation group on two directly connected devices with dynamic LACP protocol enabled, and the two devices will automatically complete the link aggregation operation through LACP negotiation. Dynamic LACP aggregation is a kind of aggregation created / deleted automatically by the system, which does not allow users to add or delete member ports in dynamic LACP aggregation. Only ports with the same speed and duplex attributes, connected to the same device, and the same basic configuration can be dynamically aggregated together. Dynamic trunking can be created even if there is only one port, which is a single-port trunking. In dynamic trunking, the LACP protocol of the port is enabled.

B) Port status in dynamic aggregation group

In a dynamic aggregation group, a port may be in two states: Selected or Standby. Both Selected port and Standby port can send and receive LACP protocol, but Standby port cannot forward user messages. Due to the limit of the maximum number of ports in the aggregation group that the device can support, if the current number of member ports exceeds the limit of the maximum number of ports, the local system and the peer system will negotiate and determine the status of the port according to the size of the port ID at the superior end of the device ID. The specific negotiation steps are as follows:

Compare device ID (system priority + system MAC address). Compare the system priority first, and then compare the system MAC address if the same. The small end of the device ID is considered to be superior.

Compare port ID (port priority + port number). For each port on the preferred side of the device ID, first compare the port priority, and then compare the port number if the priority is the same. Port ID small ports are Selected ports, and the remaining ports are Standby ports. In an aggregation group, the port in the Selected state with the lowest port number is the primary port of the aggregation group, and the other ports in the Selected state are member ports of the aggregation group.

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