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S9300, S9300E, and S9300X V200R012C00 Configuration Guide - Ethernet Switching

This document describes the configuration of Ethernet services, including configuring MAC address table, link aggregation, VLANs, VLAN aggregation, MUX VLAN, VLAN termination, Voice VLAN, VLAN mapping, QinQ, GVRP, STP/RSTP/MSTP, VBST, SEP, RRPP, ERPS, LBDT, HVRP, and Layer 2 protocol transparent transmission.
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Load Balancing Modes of Link Aggregation

Load Balancing Modes of Link Aggregation


Load balancing can be implemented on a data flow or multiple data flows to relieve the pressure on a single physical link. A data flow is a group of data frames with one or more identical attributes. The attributes include the source/destination MAC address, source/destination IP address, and source/destination TCP/UDP port number.

The following describe the two modes of load balancing:

  • Packet-based load balancing

    In packet-based load balancing, data frames of the same data flow may be transmitted over different physical links. This mode ensures optimal bandwidth utilization. However, data frames may arrive at the destination in a different order to which they were transmitted, resulting to mis-sequencing.

  • Flow-based load balancing

    Flow-based load balancing ensures that frames of the same data flow are forwarded on the same physical link and implements load balancing of flows. The system achieves this by using the hash algorithm to calculate the address in a data frame and generate a HASH-KEY value. Then the system searches for the outbound interface in the Eth-Trunk forwarding table based on the generated HASH-KEY value. Each MAC or IP address corresponds to a HASH-KEY value, so the system uses different outbound interfaces to forward data. Flow-based load balancing ensures the sequence of data transmission, but cannot ensure the bandwidth utilization.


The switch currently supports only flow-based load balancing.

Forwarding Principle

As shown in Figure 3-9, the Eth-Trunk is located at the data link layer, between the MAC address and LLC sub-layers.

Figure 3-9  Eth-Trunk in the Ethernet protocol stack

The Eth-Trunk module maintains a forwarding table that consists of the following fields:

  • HASH-KEY value

    The HASH-KEY value is calculated through the hash algorithm based on the MAC address or IP address in a data frame.

  • Interface number

    Eth-Trunk forwarding entries are limited by the number of maximum member interfaces in an Eth-Trunk. Different HASH-KEY values map to different outbound interfaces.

    For example, an Eth-Trunk supports a maximum of eight member interfaces. If physical interfaces 1, 2, 3, and 4 bundle into an Eth-Trunk, the Eth-Trunk forwarding table contains eight entries, as shown in Figure 3-10. In the Eth-Trunk forwarding table, the HASH-KEY values are 0, 1, 2, 3, 4, 5, 6, and 7, and the corresponding interface numbers are 1, 2, 3, 4, 1, 2, 3, and 4.

Figure 3-10  Example of an Eth-Trunk forwarding table

The Eth-Trunk module uses the Eth-Trunk forwarding table to forward data frames according to the following process:

  1. The Eth-Trunk module receives a data frame from the MAC sub-layer, and then extracts its source/destination MAC address or IP address.

  2. The Eth-Trunk module calculates the HASH-KEY value using the hash algorithm.

  3. Based on the HASH-KEY value, the Eth-Trunk module searches the Eth-Trunk forwarding table for the interface number, and then sends the data frame from the corresponding interface.

Load Balancing Mode

To prevent data frame mis-sequencing, an Eth-Trunk uses flow-based load balancing. Data forwarding varies depending on the load balancing mode.

According to your network requirements, you can carry out load balancing based on the following information:

  • Source MAC addresses of data frames
  • Destination MAC addresses of data frames
  • Source IP addresses of data frames
  • Destination IP addresses of data frames
  • Exclusive-Or result of source and destination MAC addresses of data frames
  • Exclusive-Or result of source and destination IP addresses of data frames
  • (Enhanced load balancing) VLAN IDs and source physical interface numbers for Layer 2, IPv4, IPv6, and MPLS data frames

When configuring a load balancing mode, pay attention to the following points:

  • The load balancing mode is only valid for the outbound interface of traffic. If traffic of the inbound interface is uneven, change the load balancing mode of the uplink outbound interface.
  • Data flows should be load balanced among all active links as much as possible. If data flows are transmitted over one link, traffic congestion may occur, affecting services.

    For example, when data frames have only one destination MAC address and IP address, use load balancing based on the source MAC address and IP address of data frames. If load balancing based on the destination MAC address and IP address is used, traffic is transmitted over one link, causing congestion.

Updated: 2019-01-18

Document ID: EDOC1100038290

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