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. Ultimate-hop popping is not available for point-to-point LSPs.

You enable ultimate-hop popping for point-to-multipoint LSPs by configuring the tunnel-services statement. When you enable ultimate-hop popping, the JUNOS software 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 software 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.

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.

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.

If you configure the tunnel-services statement on an operating router, only the behavior of newly signaled LSPs changes. Existing LSPs are not affected. To force all existing LSPs to use ultimate-hop popping, issue a clear mpls lsp command. Note that this causes all of the MPLS LSPs on the router to be signaled again.

To enable ultimate-hop popping for the egress point-to-multipoint LSPs on a router, configure the tunnel-services statement:

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

To enable ultimate-hop popping for egress point-to-multipoint LSPs, you must also configure the interface statement with the all option:

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

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