Technical Documentation

Ensuring That Secondary Paths Establish When Resources Are Diminished

The JUNOS software does not require that a primary and secondary path share the same parameters. You may decide to configure your primary paths with strict resource requirements, and configure your secondary paths with less strict requirements, allowing your secondary paths to establish more readily during periods of diminished resources.


To ensure that secondary paths establish when resources are diminished, follow these steps:

  1. In configuration mode, go to the following hierarchy level:
    [edit protocols mpls]user@host# edit label-switched-path lsp-path-name

    For example:

    [edit protocols mpls]user@R1# edit label-switched-path r1-to-r4
  2. Configure the bandwidth for the primary path, and do not configure any bandwidth for the secondary path:
    [edit protocols mpls label-switched-path lsp-path-name]user@host# set primary primary-name bandwidth bandwidth

    For example:

    [edit protocols mpls label-switched-path r1-to-r4]user@R1# set primary via-r2 bandwidth 35m
  3. Verify and commit the configuration:
    [edit protocols mpls label-switched-path lsp-path-name]user@host# show user@host# commit

Sample Output

The sample output below illustrates a bandwidth configuration on ingress router R1 in the network shown in Primary Path.

[edit protocols mpls]
user@R1# show 
label-switched-path r1-to-r4 {
     primary via-r2 {
        bandwidth 35m;
    secondary via-r7 { #  In this example, bandwidth is not configured for the secondary path. 
        standby;       #  However you could configure a bandwidth value different from 
    }                  #  that on the primary path.
[...Output truncated...]


The sample output shows the primary path via-r2 requires 35 Mbps of bandwidth, while secondary path via-r7 has no constraints. The primary path is configured with strict resource requirements, while the secondary path is configured with no bandwidth requirements, allowing the secondary path to establish more readily during periods of diminished resources. One thing to keep in mind when configuring a secondary path without bandwidth requirements is that it can be subject to traffic loss due to congestion.

Published: 2010-01-30