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Load Balancing Overview

Learn about load balancing on aggregated ethernet interfaces, and how to configure lod balancing based on MAC addresses. reduces network congestion by dividing traffic among multiple interfaces. to

Load balancing is done on Layer 2 across the member links making the configuration better without congestion and maintaining redundancy. The below topics discuss the overview of load balancing, configuring load balancing based on MAC addresses and on LAG link, understanding the consistency through resilient hashing.

Configure Load Balancing Based on MAC Addresses

The hash key mechanism for load-balancing uses L2 MAC information such as frame source and destination address. To load-balance traffic based on L2 MAC information, include the multiservice statement at the [edit forwarding-options hash-key] or [edit chassis fpc slot number pic PIC number hash-key] hierarchy level:

Use Feature Explorer to confirm platform and release support for specific features.

Review the Platform-Specific MAC Address Based Load-Balancing Behavior section for notes related to your platform.

To include the destination-address MAC information in the hash key, include the destination-mac option. To include the source-address MAC information in the hash key, include the source-mac option.

Note:
  • Any packets that have the same source and destination address will be sent over the same path.

  • You can configure per-packet load balancing to optimize EVPN traffic flows across multiple paths.

  • Aggregated Ethernet member links will now use the physical MAC address as the source MAC address in 802.3ah OAM packets.

Platform-Specific MAC Address Based Load-Balancing Behavior

Platform

Difference

ACX Series

  • ACX7000 Series routers that support MAC address-based load balancing use symmetric hashing. For example, you need to configure both source-mac and destination-mac under "multiservice" options. You cannot use source-mac and destination-mac separately.

    Note the following about hashing on ACX7000 Series Routers:

    • Do not support any default hashing. Load balancing does not happen if you do not configure "hash-key" option. Use the [set forwarding-options hash-key family] hierarchy.

    • Load balancing might or might not be symmetrical. Some links might carry more traffic than others. This traffic difference is based on the traffic profile.

    • Do not support weighted hashing.

Example: Configure Multicast Load Balancing for Use with Aggregated 10-Gigabit Ethernet Interfaces on EX8200 Switches

EX8200 switches support multicast load balancing on LAGs. Multicast load balancing evenly distributes L3 routed multicast traffic over the LAGs, You can aggregate up to twelve 10-gigabit Ethernet links to form a 120-gigabit virtual link or LAG. The MAC client can treat this virtual link as if it were a single link to increase bandwidth, provides graceful degradation as link failures occur, and increase availability. On EX8200 switches, multicast load balancing is enabled by default. However, if it is explicitly disabled, you can reenable it.

An interface with an already configured IP address cannot form part of the LAG.

Only EX8200 standalone switches with 10-gigabit links support multicast load balancing. Virtual Chassis does not support multicast load balancing.

This example shows how to configure a LAG and reenable multicast load balancing:

Requirements

This example uses the following hardware and software components:

  • Two EX8200 switches, one used as the access switch and one used as the distribution switch

  • Junos OS Release 12.2 or later for EX Series switches

Before you begin:

Overview and Topology

Multicast load balancing uses one of seven hashing algorithms to balance traffic between the individual 10-gigabit links in the LAG. For a description of the hashing algorithms, see multicast-loadbalance. The default hashing algorithm is crc-sgip. You can experiment with the different hashing algorithms until you determine the one that best balances your L3 routed multicast traffic.

When a link larger than 10 gigabits is needed on an EX8200 switch, you can combine up to twelve 10-gigabit links to create more bandwidth. This example uses the link aggregation feature to combine four 10-gigabit links into a 40-gigabit link on the distribution switch. In addition, multicast load balancing is enabled to ensure even distribution of Layer 3 routed multicast traffic on the 40-gigabit link. In the sample topology illustrated in Figure 2, an EX8200 switch in the distribution layer is connected to an EX8200 switch in the access layer.

Link speed is automatically determined based on the size of the LAG configured. For example, if a LAG is composed of four 10-gigabit links, the link speed is 40 Gbps.

The default hashing algorithm, crc-sgip, involves a cyclic redundancy check (CRC) of both the multicast packet source and group IP addresses.

Figure 2: 40-Gigabit LAG Composed of Four 10-Gigabit LinksSimplified network topology diagram showing hierarchical structure with server, distribution layer, access layer, and hosts.

You will configure a LAG on each switch and reenable multicast load balancing. When reenabled, multicast load balancing will automatically take effect on the LAG, and the speed is set to 10 Gbps for each link in the LAG. Link speed for the 40-gigabit LAG is automatically set to 40 Gbps.

Configuration

Procedure

CLI Quick Configuration
Step-by-Step Procedure

To configure a LAG and reenable multicast load balancing:

  1. Specify the number of aggregated Ethernet interfaces (aex) to be created:

  2. Specify the minimum number of links for the aex, that is, the LAG, to be labeled up:

    By default, only one link needs to be up for the LAG to be labeled up.

  3. Specify the four members to be included within the LAG:

  4. Reenable multicast load balancing:

    You do not need to set link speed the way you do for LAGs that do not use multicast load balancing. Link speed is automatically set to 40 Gbps on a 40-gigabit LAG.

  5. You can optionally change the value of the hash-mode option in the multicast-loadbalance statement to try different algorithms until you find the one that best distributes your L3 routed multicast traffic.

    If you change the hashing algorithm when multicast load balancing is disabled, the new algorithm takes effect after you reenable multicast load balancing.

Results

Check the results of the configuration:

Verification

To confirm that the configuration is working properly, perform these tasks:

Verifying the Status of a LAG Interface

Purpose

Verify that a LAG (ae0) has been created on the switch.

Action

Verify that the ae0 LAG has been created:

Meaning

The interface name aex indicates a LAG. A stands for aggregated, and E stands for Ethernet. The number differentiates the various LAGs.

Verifying Multicast Load Balancing

Purpose

Check that traffic is load-balanced equally across paths.

Action

Verify load balancing across the four interfaces:

Meaning

The interfaces should be carrying approximately the same amount of traffic.

Change History Table

Feature support is determined by the platform and release you are using. Use Feature Explorer to determine if a feature is supported on your platform.

Release
Description
10.1
Starting with Junos OS Release 10.1, you can also configure the load balancing hash key for Layer 2 traffic to use fields in the Layer 3 and Layer 4 headers using the payload statement.