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Exception for Junos LDP aggregation

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Article ID: KB29088 KB Last Updated: 19 Aug 2020Version: 2.0
Summary:

This article describes an exception to Junos LDP aggregation behavior, and provides a command for disabling the behavior.

Symptoms:

Junos allocates a single label to all IP routes when the following conditions are met:

  • All IP routes have the same next hop, and
  • The label advertised for these routes advertised by the next-hop router is also the same.

There is an exception to this behavior when the corresponding route has a back-up next hop. If, for instance, an LDP tunnel is configured and the label-switched path (LSP) link-protection is configured, the LDP routes will have a back-up next hop. In this case, Junos will not aggregate the label. Nonetheless, when the back-up next hop is gone, LDP will then aggregate the label.

Cause:

When the back-up next hop is gone, Junos will aggregate the label for routes. This may cause an LDP label change.

In addition, when the back-up next hop is back up again, Junos will deaggregate the label again, which may cause the label to change again.

Solution:

Disable the exception to this aggregation behavior. Configure the command below:

set protocols ldp deaggregate

Modification History:
2020-08-19: Updated related link.

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