350-501 Networking Practice Question
An engineer is troubleshooting MPLS LSP connectivity. The ingress PE router has the label binding for the FEC 10.1.1.0/24, but no LSP is established. Which command should be checked on the P routers to verify the LSP path?
⚠ Common exam trap
Cisco often tests the distinction between control plane (LDP neighbors, IP routes) and data plane (LFIB) verification, trapping candidates who assume LDP adjacency or IP reachability guarantees a working LSP.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
show mpls forwarding-table
The correct command is 'show mpls forwarding-table' because it displays the LFIB (Label Forwarding Information Base) on each P router. Since the ingress PE has a label binding for FEC 10.1.1.0/24 but no LSP is established, the issue likely lies in label propagation or forwarding along the path. Checking the LFIB on P routers reveals whether they have installed the correct outgoing label and interface for that FEC, which is essential for LSP connectivity.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
show mpls interface
Why it's wrong here
Shows interfaces enabled for MPLS, not forwarding entries.
- ✗
show mpls ldp neighbor
Why it's wrong here
Shows LDP neighbors, not forwarding details.
- ✓
show mpls forwarding-table
Why this is correct
Displays MPLS forwarding entries, revealing label path issues.
- ✗
show ip route 10.1.1.0
Why it's wrong here
Shows IP routing table, not MPLS forwarding.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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