350-501 Architecture Practice Question
A service provider is deploying MPLS in its core network. The core routers are all configured with LDP. Which label operation does an ingress PE perform on the first packet of a new flow?
⚠ Common exam trap
Cisco often tests the distinction between label operations at different MPLS roles (ingress, transit, egress), and the trap here is that candidates confuse the ingress push with the transit swap or egress pop operations.
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
✓
Push a new label onto the packet
The ingress PE (Provider Edge) router is the first router in the MPLS domain to receive an unlabeled IP packet. For the first packet of a new flow, the ingress PE must perform a label push operation, which adds an MPLS label (or a stack of labels) to the packet. This label is used by subsequent LSRs to forward the packet based on the label rather than the IP header, enabling MPLS forwarding.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Push a new label onto the packet
Why this is correct
The ingress PE pushes the label corresponding to the FEC for the destination.
- ✗
Remove the label stack entirely
Why it's wrong here
Removal of the entire label stack is done at the egress PE.
- ✗
Pop the label (PHP)
Why it's wrong here
PHP happens at the penultimate hop to reduce load on the egress PE.
- ✗
Swap the incoming label for an outgoing label
Why it's wrong here
Swapping is performed at intermediate LSRs, not at the ingress PE.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-501 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-501 exam.