350-501 Architecture Practice Question
A service provider is troubleshooting an L2VPN where a CE is unable to ping the remote CE. The PE-CE interfaces are up, and the pseudowire status shows 'up'. Which two actions should be taken to further isolate the issue? (Choose two.)
⚠ Common exam trap
Cisco often tests the misconception that a pseudowire status of 'up' guarantees end-to-end connectivity, when in fact control-plane up does not ensure data-plane forwarding if parameters like VC ID or MTU are mismatched.
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
✓
Verify the VC ID match on both PEs
The VC ID (Virtual Circuit ID) must match on both PEs for the pseudowire to be established correctly. If the VC IDs are mismatched, the pseudowire status may show as 'up' due to local signaling, but traffic will not be forwarded between the CEs because the pseudowire endpoints are not logically connected. Verifying the VC ID ensures that the L2VPN circuit is properly configured end-to-end.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Check the MAC address table on the CE
Why it's wrong here
MAC address table is not used in point-to-point L2VPN; it's transparent.
- ✗
Check the LDP session between PEs
Why it's wrong here
The LDP session is already established because pseudowire is up.
- ✗
Verify the VFI configuration on the PE
Why it's wrong here
VFI is used for VPLS, not for point-to-point L2VPN.
- ✓
Verify the VC ID match on both PEs
Why this is correct
Mismatched VC IDs can cause traffic to be dropped despite pseudowire being up.
- ✓
Verify the MTU consistency on the pseudowire
Why this is correct
MTU mismatch can cause packet drops, especially if end-to-end MTU is not aligned.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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