The implicit null label option allows an egress LER to receive MPLS packets from the previous hop without the outer LSP label. The user can configure to signal the implicit operation of the previous hop is referred to as penultimate hop popping (PHP). This option is signaled by the egress LER to the previous hop during the FEC signaling by the LDP control protocol.
Enable the use of the implicit null option, for all LDP FECs for which this node is the egress LER, using the following command:
config>router>ldp>implicit-null-label
When the user changes the implicit null configuration option, LDP withdraws all the FECs and re-advertises them using the new label value.