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Configuring and Verifying Load Balancing

Purpose

Load balancing is configured on the ingress router and uses the hash algorithm to distribute traffic equally across paths. The hash algorithm is designed to distribute packets to prevent any single link from being saturated. Before you can configure and verify load balancing in an MPLS network, you must have all the necessary MPLS components and protocols configured correctly. For information on configuring an MPLS network, see the Junos MPLS Network Operations Guide.

Keep the following information in mind when you configure load balancing:

The load-balance per packet policy is configured on an ingress router with more than one LSP configured to the same egress router.
Load balancing offers no guarantee of equal distribution of traffic over equal-cost links, nor does it guarantee that increasing the number of Internet flows will create a better hash distribution.

To configure and verify load balancing, follow these steps:

Define a Load-Balancing Policy

Purpose

On the ingress or transit router, you can include a policy statement that performs load balancing on all routes. For information on including a policy statement that performs load balancing on specific routes, see “Configuring Per-Packet Load Balancing” in the Junos Routing Protocols Configuration Guide.

Action

On the ingress or transit router, to define a load-balancing policy for all routes, follow these steps:

In configuration mode, go to the following hierarchy level:
[edit]user@host# edit policy-options
Define the load-balance policy and action:
[edit policy-options]user@host# set policy-statement policy-name then load-balance per-packet
Verify and commit the configuration:
user@host# showuser@host# commit

Sample Output

user@R6> edit 
Entering configuration mode

[edit]
user@R6# edit policy-options  

[edit policy-options]
user@R6# set policy-statement load-balance-traffic then load-balance per-packet  

[edit policy-options]
user@R6# show  
policy-statement load-balance-traffic {
    then {
        load-balance per-packet;
    }
}

[edit policy-options]
user@R6# commit  
commit complete

Meaning

The sample output from ingress router R6 shows the process for configuring load balancing. On an Internet Processor I ASIC, packets with the same parameters are spread across multiple equal-cost next hops; while an Internet Processor II ASIC sends packets with the same parameters to the same next hop, since they are in the same flow. The Junos OS command to turn on load balancing uses the action load-balance per-packet, which is misnamed in relation to the Internet Processor II ASIC. On the Internet Processor II ASIC, this command actually enables per-flow load balancing.

Apply the Load-Balancing Policy to the Forwarding Table

Purpose

Apply the policy configured in Step 1 to routes exported from the routing table to the forwarding table.

Action

To apply a load-balancing policy to the forwarding table, follow these steps:

In configuration mode, go to the following hierarchy level:
[edit]user@host# edit routing-options
Define a load-balance per packet action:
[edit routing-options]user@host#set forwarding-table export policy-name
Verify and commit the configuration:
user@host# showuser@host# commit

Sample Output

[edit]
user@R6# edit routing-options 

[edit routing-options]
user@R6# set forwarding-table export load-balance-traffic 

[edit routing-options]
user@R6# show 
static {
[...Output truncated...]
}
router-id 192.168.6.1;
autonomous-system 65432;
forwarding-table {
    export load-balance-traffic;
}

[edit routing-options]
user@R6# commit  
commit complete

Meaning

The sample output shows the process for applying a load-balancing policy to export routes from the routing table to the forwarding table.

Verify That Load Balancing Is Working

Purpose

After configuring load balancing, check that traffic is load-balanced equally across paths. In this section, the command output reflects the load-balancing configuration of the example network shown in Load-Balancing Network Topology. The clear commands are used to reset LSP and interface counters to zero so that the values reflect the operation of the load-balancing configuration.

Action

To verify load balancing across interfaces and LSPs, use the following command on the ingress router:

user@host# show configuration

To verify load balancing across interfaces and LSPs, use the following commands on a transit router:

user@host# show route user@host# show route forwarding-table user@host# show mpls lsp statistics user@host# monitor interface traffic user@host# clear mpls lsp statistics user@host# clear interface statistics

Sample Output

The following sample output is for the configuration on ingress router R1:

user@R1> show configuration | no-more  
[...Output truncated...]
routing-options {
    [...Output truncated...]
     forwarding-table {
        export lbpp;
    }
}
[...Output truncated...]
policy-options {
     policy-statement lbpp {
        then {
            load-balance per-packet;
        }
    }
}

Meaning

The sample output for the show configuration command on ingress router R1 shows that load balancing is correctly configured with the lbpp policy statement. Also, the lbpp policy is exported into the forwarding table at the [edit routing-options] hierarchy level.

Sample Output