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

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.

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.

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

set protocols ldp deaggregate

2020-08-19: Updated related link.

• Configuring LDP FEC Deaggregation