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Example: Weighted ECMP Traffic Distribution on One-Hop IS-IS Neighbors

This example shows how to configure weighted equal cost multipath (ECMP) routing for distributing traffic to IS-IS neighbors that are one hop away to ensure optimal load balancing. Weighted ECMP routing distributes traffic unequally over multiple paths for better load balancing. However, weighted ECMP routing is more efficient than equal distribution of traffic during per-packet load balancing.

Requirements

This example uses the following hardware and software components:

  • Two MX Series routers

  • Junos OS Release 15.1F4 or later

Before you configure weighted ECMP in an IS-IS network, make sure you :

  1. Configure IP addresses on the device interfaces.

  2. Configure IS-IS.

  3. Configure load balancing

  4. Configure a per-packet load balancing policy.

Overview

Beginning with Junos OS Release 15.1F4, you can configure the IS-IS protocol to get the logical interface bandwidth information associated with the gateways of equal-cost multipath (ECMP) next hop. During per-packet load balancing, traffic distribution is based on the available bandwidth to facilitate optimal bandwidth usage for incoming traffic on an ECMP path of one hop distance. The Packet Forwarding Engine does not distribute the traffic equally, but considers the balance values and distributes the traffic according to the bandwidth availability. However, this feature is not available for ECMP paths that are more than one hop away.

Topology

In Figure 1, three aggregated Ethernet bundles ae0, ae1, and ae2 with four links each, are configured between Router R0 and Router R1. The Packet Forwarding Engine distributes traffic unequally between the three Ethernet bundles when one of the links goes down, depending on the available bandwidth.

Figure 1: Weighted ECMP Traffic Distribution on One Hop IS-IS NeighborsWeighted ECMP Traffic Distribution on One Hop IS-IS Neighbors

Configuration

CLI Quick Configuration

To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, copy and paste the commands into the CLI at the [edit] hierarchy level, and then enter commit from configuration mode.

Router R0

Router R1

Configuring Router R0

Step-by-Step Procedure

The following example requires that you navigate various levels in the configuration hierarchy. For information about navigating the CLI, see Using the CLI Editor in Configuration Mode in the CLI User Guide.

To configure Router R0:

Note:

Repeat this procedure for Router R1 after modifying the appropriate interface names, addresses, and other parameters.

  1. Specify the maximum number of weighted ECMP interfaces that you want to configure. Enable graceful switchover and specify the number of aggregated Ethernet interfaces to be created.

  2. Configure the interfaces with multiple links to the same destination for load balancing traffic.

  3. Configure logical interfaces with appropriate bandwidth based on the underlying physical bandwidth.

    Note:

    For logical interfaces, configure interface bandwidth to distribute traffic across equal-cost multipaths based on the underlying operational interface bandwidth. When you configure multiple logical interfaces on a single interface, configure appropriate logical bandwidth for each logical interface to see the desired traffic distribution over the logical interfaces.

  4. Configure IP addresses on the interfaces with either IPv4 or IPv6 addresses, as per your network requirements.

  5. Configure the four member links of the ae0 aggregated Ethernet bundle.

  6. Configure the four member links of the ae1 aggregated Ethernet bundle.

  7. Configure the four member links of the ae2 aggregated Ethernet bundle.

  8. Configure IP address and the Link Aggregation Control Protocol (LACP) for ae0 aggregated Ethernet interface.

  9. Configure IP address and the Link Aggregation Control Protocol (LACP) for ae1 aggregated Ethernet interface.

  10. Configure IP address and the Link Aggregation Control Protocol (LACP) for ae2 aggregated Ethernet interface.

  11. Configure the loopback interface address and iso family address.

  12. Configure IS-IS on all the interfaces and on the AE bundles.

  13. Configure per-packet load balancing.

  14. Apply per-packet load balancing policy.

  15. Enable weighted ECMP traffic distribution on directly connected IS-IS neighbors.

Results

From configuration mode, confirm your configuration by entering the show chassis, show interfaces, show protocols, show policy-options, and show routing-options commands. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

Verification

Confirm that the configuration is working properly.

Verifying Equal Distribution of Traffic Over Equal-Cost Multiple Paths

Purpose

To verify that traffic is equally distributed over the aggregated Ethernet bundles.

Action

From operational mode, enter the show route 198.0.0.1 extensive command.

Meaning

IS-IS distributes traffic equally when the three aggregated Ethernet bundles have the same bandwidth available.

Verifying Unequal Traffic Distribution Over Available Bandwidth

Purpose

To verify that IS-IS distributes traffic unevenly when one of the aggregated link is down during per-packet load balancing depending on the available bandwidth.

Action

Disable one of the links on the ae0 bundle so that the available bandwidth is 3g on ae0 and 4g on ae1and ae2. From operational mode, enter the show route 198.0.0.1 extensive command.

Meaning

IS-IS infers that the ae0 bundle has only 3g of bandwidth available. Therefore, modifies per-packet load balancing according to the available bandwidth. As per the output, only 27 percent of the bandwidth is available on ae0 because one of the aggregated Ethernet links is down. Thus IS-IS distributes traffic unequally depending on the available bandwidth.

Verifying Unequal Traffic Distribution onLogical Interfaces

Purpose

To verify that IS-IS distributes traffic unevenly on logical interfaces based on the configured logical bandwidth.

Action

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
15.1F4
Beginning with Junos OS Release 15.1F4, you can configure the IS-IS protocol to get the logical interface bandwidth information associated with the gateways of equal-cost multipath (ECMP) next hop.