350-501 Architecture Practice Question
In an MPLS VPN, what label operation does the egress PE perform on the VPN packet before forwarding it to the CE?
⚠ Common exam trap
Cisco often tests the distinction between label operations at different MPLS nodes; the trap here is confusing the egress PE's role with that of the ingress PE (which imposes labels) or a transit P router (which swaps labels), leading candidates to select 'Swap the top label' or 'Push a new label'.
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
✓
Pop the label stack
In an MPLS VPN, the egress PE (Provider Edge) router receives a packet with a label stack typically consisting of a transport label (IGP label) and a VPN label. Before forwarding the IP packet to the CE (Customer Edge), the egress PE must remove the entire MPLS label stack because the CE is an IP-only device that does not understand MPLS labels. This operation is called 'pop the label stack' (also known as penultimate hop popping, though at the egress PE it is explicit label removal).
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Swap the top label
Why it's wrong here
Swap is done at intermediate LSRs, not at the egress.
- ✗
Impose a VPN label
Why it's wrong here
Impose is done at ingress.
- ✓
Pop the label stack
Why this is correct
The egress PE removes all labels and forwards the IP packet.
- ✗
Push a new label
Why it's wrong here
Push is done at ingress PE.
- ✗
Replace the transport label
Why it's wrong here
Replacement is not typical; swap or pop.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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