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CLI-based Configuration Guide - Ethernet Switching

AR650, AR1600, and AR6100 V300R003

This document describes how to configure the components for LAN services, including link aggregation groups, VLANs, voice VLANs, MAC address tables, transparent bridging, as well as GVRP, STP/RSTP, and MSTP protocols.
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Load Balancing Modes of Link Aggregation

Load Balancing Modes of Link Aggregation


A data flow is a group of data packets with one or more identical attributes. The attributes include the source MAC address, destination MAC address, source IP address, destination IP address, source TCP/UDP port number, and destination TCP/UDP port number.

Load balancing falls into packet- and flow-based load balancing.

  • Packet-based load balancing

    There are multiple physical links between both devices of the Eth-Trunk, so the first and second data frames of the same data flow may be transmitted over two physical links. In this case, the second data frame may arrive at the remote device earlier than the first data frame. As a result, packet mis-sequencing occurs.

  • Flow-based load balancing

    The system uses the hash algorithm to calculate the address in a data frame and generates 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. This mode ensures that frames of the same data flow are forwarded on the same physical link and implements load balancing of flows. Flow-based load balancing ensures the sequence of data transmission, but cannot ensure the bandwidth utilization.

Forwarding Principle

As shown in Figure 2-9, the Eth-Trunk is located between the MAC address layer and the LLC sub-layer, that is, data link layer.

Figure 2-9  Eth-Trunk in the Ethernet protocol stack

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

  • HASH-KEY value

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

  • Interface number

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

    For example, an Eth-Trunk supports a maximum of eight member interfaces. If physical interfaces 1, 2, 3, and 4 are bundled into an Eth-Trunk, the Eth-Trunk forwarding table contains four entries, as shown in Figure 2-10. 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 2-10  Example of an Eth-Trunk forwarding table

The Eth-Trunk module forwards a packet according to the Eth-Trunk forwarding table:

  1. The Eth-Trunk module receives a packet 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 packet from the corresponding interface.

Load Balancing Mode

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

You can use the following load balancing modes according to the actual networking:

  • Based on source MAC addresses of packets
  • Based on destination MAC addresses of packets
  • Based on source IP addresses of packets
  • Based on destination IP addresses of packets
  • Based on the Exclusive-Or result of source and destination MAC addresses of packets
  • Based on the Exclusive-Or result of source and destination IP addresses of packets

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 and service running is affected.

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

Updated: 2019-04-12

Document ID: EDOC1100041791

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