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Enabling Ultimate-Hop Popping on Point-to-Multipoint LSPs

By default, for both point-to-point and point-to-multipoint LSPs, penultimate-hop popping is used for MPLS traffic. MPLS labels are removed from packets on the router just before the egress router of the LSP. The plain IP packets are then forwarded to the egress router. For ultimate-hop popping, the egress router is responsible for both removing the MPLS label and processing the plain IP packet.

It can be beneficial to enable ultimate-hop popping on point-to-multipoint LSPs, particularly when transit traffic is traversing the same egress device. If you enable ultimate-hop popping, a single copy of traffic can be sent over the incoming link, saving significant bandwidth. By default, ultimate-hop popping is disabled.

You enable ultimate-hop popping for point-to-multipoint LSPs by configuring the tunnel-services statement. When you enable ultimate-hop popping, the Junos OS selects one of the available virtual loopback tunnel (VT) interfaces to loop back the packets to the PFE for IP forwarding. By default, the VT interface selection process is performed automatically. Bandwidth admission control is used to limit the number of LSPs that can be used on one VT interface. Once all the bandwidth is consumed on one interface, the Junos OS selects another VT interface with sufficient bandwidth for admission control.

If an LSP requires more bandwidth than is available from any of the VT interfaces, ultimate-hop popping cannot be enabled and penultimate-hop popping is enabled instead.

For ultimate-hop popping on point-to-multipoint LSPs to function properly, the egress router must have a PIC that provides tunnel services, such as the tunnel services PIC or the adaptive services PIC. Tunnel services are needed for popping the final MPLS label and for returning packets for IP address lookups.

You can explicitly configure which VT interfaces handle the RSVP traffic by including the devices option for the tunnel-services statement. The devices option allows you to specify which VT interfaces are to be used by RSVP. If you do not configure this option, all of the VT interfaces available to the router can be used.

• [edit protocols rsvp]
• [edit logical-systems logical-system-name protocols rsvp]

You must configure this statement at the [edit protocols rsvp] hierarchy level.