Figure 50: Ldp Over Rsvp Application Variant - Alcatel-Lucent 7450 Manual

Ethernet service switch

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Label Distribution Protocol

one area to another. Note that only the user packets are tunneled over the RSVP LSPs. The T-LDP

control messages are still sent unlabeled using the IGP shortest path.

Note that in this application, the bi-directional RSVP LSP tunnels are not treated as IP interfaces

and are not advertised back into the IGP. A PE must always rely on the IGP to look up the next hop

for a service packet. LDP-over-RSVP introduces a new tunnel type, tunnel-in-tunnel, in addition

to the existing LDP tunnel and RSVP tunnel types. If multiple tunnels types match the destination

PE FEC lookup, LDP will prefer an LDP tunnel over an LDP-over-RSVP tunnel by default.

The design in

allows a service provider to build and expand each area independently

without requiring a full mesh of RSVP LSPs between PEs across the three areas.

In order to provide a VLL service, PE1 and PE2 are still required to set up a targeted LDP session

directly between them. Again a 3 label stack is required, the RSVP LSP label, followed by the

LDP label for the loopback address of the destination PE, and finally the pseudowire label (VC

This implementation supports a variation of the application in

49, in which area 1 is an

LDP area. In that case, PE1 will push a two label stack while ABR1 will swap the LDP label and

push the RSVP label as illustrated in

50. LDP-over-RSVP tunnels can also be used as IGP

Metro Network

(RSVP Area 2)

(LDP Area 1)

Core Network

(RSVP Area 3)

OSSG129A7450

Figure 50: LDP over RSVP Application Variant

7450 ESS MPLS Guide