How to determine the type of label allocated on the penultimate hop

By default, the egress node assigns implicit-null labels to the penultimate hop. When an implicit-null label is assigned to an LSR, the LSR directly pops the labels without having to replace the label at the top of the stack with this implicit-null label. If the penultimate hop adds a label to the label stack, the label distribution mode has been changed.

Typical failure: In the MPLS view, the label assigned to the penultimate hop is explicit-null or non-null. The penultimate hop is assigned a label other than 3. You can check the label distribution mode according to the configuration in the MPLS view.

Solution: Configure the PHP feature in the MPLS view and set the label distribution mode to implicit-null. Or you can delete the configuration of the label distribution mode.

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