350-501 Architecture Practice Question
Which TWO are functions of the MPLS data plane?
⚠ Common exam trap
Cisco often tests the distinction between control plane and data plane functions, and the trap here is that candidates mistakenly associate label distribution (LDP) or routing protocol operations (BGP, OSPF) with the data plane, when in fact they are control plane processes that support but do not execute packet forwarding.
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
✓
Label push at ingress LSR
The MPLS data plane is responsible for the actual forwarding of packets based on labels. At the ingress LSR, the data plane performs a label push operation, which involves inserting a new MPLS label (or a stack of labels) onto the incoming IP packet before forwarding it into the MPLS domain. This action is a fundamental data-plane function, as it directly manipulates the packet header to enable label switching.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Label push at ingress LSR
Why this is correct
Pushing a label is a data plane operation.
- ✗
Label distribution via LDP
Why it's wrong here
LDP is a control plane protocol.
- ✓
Label swap at transit LSR
Why this is correct
Swapping labels is done in the data plane.
- ✗
Metric calculation for routing
Why it's wrong here
Metric calculation is part of IGP control plane.
- ✗
Route exchange via BGP
Why it's wrong here
BGP is a control plane protocol.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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