Implicit Null Label

The implicit null label option enables an eLER to receive MPLS packets from the previous-hop LSR without the outer LSP label.

The implicit null label is included in RESV messages sent by the eLER to the previous-hop LSR. When the implicit null label is signaled to the LSR, it pops the outer label before sending the MPLS packet to the eLER; this is known as penultimate hop popping.

The implicit null label option can be enabled for all RSVP-TE interfaces and for all RSVP-TE LSPs for which the router is the eLER by using the implicit-null-label command in the config>router>rsvp context.

RSVP-TE must be shut down before this command can be used.

The implicit null label option can also be enabled or disabled on a specific RSVP-TE interface, overriding the RSVP-TE level configuration, by using the implicit-null-label {enable | disable} command in the config>router>rsvp>interface context.

The implicit null label is enabled for all LSPs for which the router is the eLER and for which the PATH message is received from the previous-hop LSR over the RSVP-TE interface.

With facility backup, if the eLER is also the merge point (MP) node, the incoming interface for the PATH refresh message over the bypass tunnel dictates whether the packet will use the implicit null label. Similarly, with one-to-one backup, if the eLER is also the detour merge point (DMP) node, the incoming interface for the PATH refresh message over the detour LSP dictates whether the packet will use the implicit null label.

The RSVP-TE interface must be shut down before this command can be used.