Ethernet LAG

The link aggregation group (LAG) aggregates multiple links. Each LAG is used as a link to extend the bandwidth and improve the link reliability.

Overview

Ethernet link aggregation is to configure multiple physical Ethernet ports to one logical port.

The LAG has the following functions:

Link reliability improvement: In an LAG, member links dynamically back up each other. If a working link is interrupted, the backup link takes over its work immediately.
Link capacity expansion: By binding multiple physical links, you can obtain a data link with higher bandwidth, without upgrading the existing equipment. The capacity equals the sum of the capacity of all the physical links. The aggregation module allocates the traffic to different LAG members, to realize the link-level load sharing.

The ports for aggregation must meet the following requirements:

Working mode: Full-duplex mode must be used. The working mode cannot be auto-negotiation and must be a specified mode.
Port rate: Rates of the ports for aggregation must be consistent.
Standby port: A main port and a corresponding standby port need be defined in an LAG. A main port can be added to the link aggregation group, regardless of the service. A standby port can be, however, added to the link aggregation group only if no services are available. After being added to the link aggregation group, a standby port cannot be configured with any services.

The LAG is classified into the following types:

According to the modes of processing load, the LAG is classified into load sharing LAG and non-load sharing LAG.
- Load sharing: In an LAG, all the ports transmit data services to extend the bandwidth. If a port fails or the fiber or wire is cut on the physical line connected to the port, this port does not share data services but the services are sent or transmitted normally.
- Non-load sharing: In an LAG, only one port transmits data services in the working state, and the other ports are in the backup state. If the working port fails or the fiber or wire is cut on the physical line connected to the working port, a backup port enters the working state to transmit services.
According to the location of the protection physical interface, the LAG is classified into intra-board LAG and DLAG.
- Intra-board LAG: Ethernet ports on one data board of the equipment are configured as a port aggregation group.
- DLAG: Ethernet ports on two data boards of the equipment are configured as a port aggregation group.

Compliant protocol: The LAG complies with the IEEE 802.3ad.

Intra-Board LAG

The LAG works at the data link layer between the MAC sub-layer and logical link control (LLC) sub-layer. Figure 1 illustrates the principle of the LAG.

Figure 1 LAG

The LAG has the following modes of aggregation. SeeTable 1.

**Table 1** The LAG has the following modes of aggregation.
The modes of aggregation	Concept	Whether the LACP protocol runs	Application	Supporting of the U2000 Web LCT
Dynamic aggregation	The LAG supports automatic configuration. That is, the independent links are automatically configured to an LAG without manual operations.	Yes	Dynamic aggregation enables the system to have the plug and play feature. In practice, however, this aggregation mode brings the user operating troubles. For example, if the system generates an LAG dynamically, the LAG ID may change when the system restarts. This brings troubles in equipment management.	No
Manual aggregation	The LAG is created manually but not generated automatically by the system. In an LAG, the member links are fixed and need be modified manually, because the system does not add the links to or remove them from the LAG. During aggregation, there is not any aggregation negotiation between the equipment at the two ends.	No	The LAG and member links are managed manually and thus they are fixed. This facilitates the aggregation management. In this mode, however, the LACP protocol is not used. Systems at the two ends of a link do not negotiate with each other for the aggregation. As a result, the aggregation is not controlled effectively. For example, if you incorrectly connect physical links to different equipment or to the ports that cannot be aggregated on the same equipment, the system cannot detect this error.	Yes
Static aggregation	You need to configure aggregation ports of the equipment at the two ends. Based on the LACP protocol, the equipment at the two ends transmits packets to each other to communicate and negotiate, and to report errors and faults. The LACP protocol determines whether to aggregate or deaggregate the ports.	Yes	This mode supports the LACP protocol. This facilitates the interconnection with routers and switches and the protection of services. Manual management of LAGs and member links means that you need to manually create and delete an LAG, and add links to or remove them from the LAG. The system does not perform these operations automatically, or modify your configuration result. In a static LAG, the member ports can be in the SELECTED or STANDBY state. The port in SELECTED state is the working port that has traffic. The port in STANDBY state is the standby port that has not any traffic. Therefore, in a static LAG, all the member ports may not be working at the same time. The state of a port changes with the system running and external environment.	Yes