Boost Bandwidth and Reliability with Link Aggregation: Principles and Config Guide

Background

As network scale expands, users demand higher bandwidth and reliability on backbone links. Traditional methods replace high‑speed interface boards or devices, which is costly and inflexible. Link aggregation increases bandwidth without hardware upgrades by bundling multiple physical interfaces into a logical one, also providing backup links for improved reliability.

Application Scenario

In enterprise networks, all device traffic converges at the core layer before forwarding to other networks or the Internet. Core devices can become congested; deploying link aggregation at the core enhances overall data throughput and alleviates congestion.

Link Aggregation Basics

Link aggregation combines several physical links between two devices into a single logical link. It can include up to eight member links (default on ARG3 routers and X7 switches). The aggregated bandwidth equals the sum of member link bandwidths, and the mechanism provides load balancing and redundancy.

Key Benefits

Increases logical link bandwidth by aggregating member links.

Improves reliability: if a member link fails, traffic shifts to remaining active links.

Enables load balancing across member links, reducing congestion.

Link Aggregation Modes

Manual Load‑Balancing Mode

Members are added manually without a control protocol. All active links forward traffic and share load evenly. If a link fails, traffic is redistributed among remaining links. Suitable when devices do not support LACP.

Static LACP Mode

Devices exchange LACP packets to negotiate aggregation parameters, then determine active and standby interfaces. A static (M:N) mode designates active member links for data forwarding and non‑active links for backup.

Data Flow Control

All member interfaces must share identical parameters (speed, duplex, flow control). Data frames must preserve order; to avoid out‑of‑order delivery, Etn‑Trunk uses per‑flow hashing based on MAC/IP addresses, ensuring each flow uses a single physical link while balancing overall traffic.

Basic Configuration

Example commands (Huawei syntax): interface Eth-Trunk 1 Creates an Eth‑Trunk interface and enters its view. If the trunk already exists, the command directly enters its view.

Configuration Rules

Only delete Eth‑Trunk interfaces without member ports.

Layer‑2 trunks must have layer‑2 member ports; layer‑3 trunks must have layer‑3 member ports.

Maximum of 8 member ports per trunk.

Member ports must be hybrid interfaces.

An Eth‑Trunk cannot be a member of another trunk.

An Ethernet interface can belong to only one trunk.

All member ports must be of the same type (e.g., all 1 GbE).

Ports on different line cards can be aggregated together.

Different speed members may cause congestion and packet loss.

After adding ports, the trunk learns MAC addresses; member ports stop learning.

Viewing Link Aggregation Information

Use display interface eth-trunk <trunk-id> to verify aggregation status, collect traffic statistics, and detect port faults. Interface states: UP (operational), DOWN (physical fault), Administratively Down (manually disabled).

Three‑Layer Link Aggregation

To configure a layer‑3 trunk, create the Eth‑Trunk, then execute undo portswitch to convert it to a layer‑3 interface and assign an IP address.

Link Aggregation Protocols

LACP (IEEE 802.3ad) is the standard protocol for dynamic aggregation; static aggregation does not require a protocol. PAGP is Cisco‑specific.

LACP Use Cases

Expanding bandwidth when existing links are saturated.

Providing dynamic backup between member ports.

LACP exchanges LACPDU packets to negotiate and maintain the aggregation.

LACP Negotiation Modes

Dynamic aggregation ports default to a management key of zero.

Static aggregation ports use the trunk ID as the management key.

Viewing LACP Configuration

Use display link-aggregation summary (or equivalent) to see protocol settings and member status.