LDP uses non-null labels in any of the following scenarios:


1.If the non-null mode is specified in the MPLS view, the egress needs to assign a non-null label to the penultimate hop.

2.When receiving a Label Mapping message from a neighbor and replying with no Label Release message, the LSR uses a non-null label to set up an LSP including the liberal LSP.

3.The non-null label is used when an Transit LSP is set up.

4.In a remote LDP session, if no downstream local session is set up and the policy for triggering the establishment of an LSP is all, an LSR, functioning as an agent egress, assigns a non-null label to each FEC except for the local route.

Do you have some topologies to share where this apply? Usually the label is taken out in the penultimate hop by default

good info