The implicit null label option allows a 7210 SAS egress LER to receive MPLS packets from the previous hop without the outer LSP label. The 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.
The router can be configured to signal the implicit null label value over all RSVP interfaces and for all RSVP LSPs which have this node as the egress LER. In addition, the egress LER can be configured to receive MPLS packet with the implicit null label on a static LSP.
The following CLI command is used to configure the router:
config>router>ldp>implicit-null-label
RSVP must be shut down before changing the implicit null configuration option.