hardMultiple Select
350-401 Practice Question: Which three statements about MPLS forwarding are…
Which three statements about MPLS forwarding are true? (Choose three.)
⚠ Common exam trap
The trap is mixing up the LIB and LFIB: candidates often think the LIB is used for forwarding, but the LIB is the control-plane database of all learned labels, while the LFIB is the forwarding table with only the best entries.
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
✓
MPLS forwarding uses the Label Forwarding Information Base (LFIB) to make forwarding decisions.
Option A is correct because MPLS forwarding decisions are made by matching the incoming label against the Label Forwarding Information Base (LFIB), which maps an incoming label to an outgoing label and next-hop interface. Option B is correct because the LFIB is populated by label distribution protocols such as LDP, which binds labels to routes and advertises them to neighbors. Option C is correct because the Label Information Base (LIB) holds all label bindings learned from LDP neighbors, while the LFIB contains only the best/selected entries actually used for forwarding labeled packets. Option D is incorrect because the FIB is used for IP forwarding lookups, not for MPLS label lookups. Option E is incorrect because the RIB is used by routing protocols to select best routes and populate the FIB/LFIB, but it is not consulted directly for MPLS forwarding decisions.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
MPLS forwarding uses the Label Forwarding Information Base (LFIB) to make forwarding decisions.
Why this is correct
MPLS forwarding is label-swapping driven: the LFIB maps an incoming label and interface to an outgoing label and next hop, and the router consults it for every labelled packet. This makes the LFIB the authoritative data plane structure for forwarding decisions.
- ✓
The LFIB is populated by label distribution protocols such as LDP.
Why this is correct
Label distribution protocols such as LDP advertise prefix-to-label bindings between adjacent routers; the router selects best bindings and installs them into the LFIB, which drives label swapping. This correctly identifies LDP as the control plane source populating the forwarding table.
- ✓
The LIB stores all labels learned from LDP neighbors, but the LFIB is used for actual forwarding.
Why this is correct
The LIB is the control plane table holding all label bindings learned from LDP neighbours, including non-best labels, while the LFIB is the data plane table containing only the selected incoming-to-outgoing label mappings actually used to forward packets, so the statement correctly distinguishes their roles.
- ✗
MPLS forwarding uses the Forwarding Information Base (FIB) for label lookups.
Why it's wrong here
Label lookups occur in the Label Forwarding Information Base, which maps incoming labels to outgoing labels and interfaces; the FIB holds IP prefix entries instead. It tempts because the FIB does drive forwarding decisions, so it would be correct when describing unlabelled IP packet forwarding.
- ✗
MPLS forwarding uses the Routing Information Base (RIB) to determine the next hop.
Why it's wrong here
MPLS forwarding consults the Label Forwarding Information Base, not the RIB; the RIB is the control-plane table populated by routing protocols. It tempts because the RIB does determine next hops for IP routing, so it would be correct when describing conventional destination-based IP forwarding.
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
This 350-401 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 350-401 exam.