Objectives
The simulator ticks each one as soon as the network meets it.
Use Loopback0 as the LDP router ID on PE1, P and PE2 (mpls ldp router-id Loopback0 force).
Enable LDP on every core interface (mpls ip).
Check show mpls ldp neighbor: PE1–P and P–PE2 are in state Oper.
Check show mpls forwarding-table on PE1: 3.3.3.3/32 has an outgoing label from P.
Check P: it shows Pop Label for 3.3.3.3/32 (penultimate-hop popping).
From PE1, traceroute 3.3.3.3 source Loopback0.
Before you start
Cisco enables LDP on an interface with mpls ip. The LDP router ID must be reachable through the IGP, so pin it to Loopback0. The egress router advertises implicit null (label 3), so the router before it pops the label.
Concept
MPLS labels and LDP
MPLS forwards packets by a short label instead of looking up the IP address at every hop. LDP gives each IGP prefix a label on every router and shares it with neighbors, building a label-switched path (LSP) through the core.
