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350-401 Practice Question: Which three statements about MPLS traffic…
Which three statements about MPLS traffic engineering (MPLS-TE) are true? (Choose three.)
⚠ Common exam trap
The trap here is conflating LDP (used for IGP-based label distribution) with RSVP-TE (used for TE tunnel signaling) — candidates who remember 'MPLS uses LDP' often wrongly pick option D.
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-TE uses RSVP-TE to signal LSPs and reserve resources.
Option A is correct because MPLS-TE uses RSVP-TE as its signaling protocol to establish label-switched paths (LSPs) and reserve bandwidth resources along the explicit path. Option B is correct because OSPF and IS-IS are extended with TE extensions (OSPF-TE and IS-IS-TE) to flood TE link attributes such as available bandwidth, administrative groups, and link metrics in the TE database. Option C is correct because MPLS-TE's core purpose is to route traffic over explicitly defined paths that can deviate from the IGP shortest path, enabling constraint-based routing and load balancing. Option D is incorrect because LDP distributes labels for hop-by-hop IGP-based LSPs and does not perform the resource reservation or explicit path signaling required for TE tunnels. Option E is incorrect because BGP is a path-vector routing protocol used for inter-domain routing and does not compute paths for TE LSPs; path computation is done by the headend router using the TE database (CSPF).
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-TE uses RSVP-TE to signal LSPs and reserve resources.
Why this is correct
RSVP-TE is the signalling protocol that establishes label-switched paths and reserves bandwidth along an explicit route, satisfying the stem's requirement for a true MPLS-TE statement. It carries the explicit route object and reservation parameters, distinguishing MPLS-TE from plain label distribution.
- ✓
OSPF or IS-IS can be extended to carry TE link attributes.
Why this is correct
MPLS-TE relies on link attributes such as bandwidth and affinity being flooded through the IGP, and both OSPF and IS-IS have TE extensions for this purpose. This satisfies the stem's requirement for true MPLS-TE statements.
- ✓
MPLS-TE allows traffic to follow paths that differ from the IGP shortest path.
Why this is correct
MPLS-TE computes constrained paths using CSPF rather than inheriting the IGP shortest path, so traffic can be steered onto underutilised links. This explicit-route capability satisfies the stem directly, enabling load balancing and avoidance of congested or failed segments.
- ✗
MPLS-TE relies on LDP to distribute labels for TE tunnels.
Why it's wrong here
TE tunnels are signalled by RSVP-TE, which distributes labels along the explicit path; LDP distributes labels for IGP-derived shortest paths only and cannot reserve bandwidth or honour explicit routes. It is tempting because LDP does distribute MPLS labels, but not for TE LSPs.
- ✗
MPLS-TE uses BGP to compute the best path for TE LSPs.
Why it's wrong here
Path computation for TE LSPs is performed by CSPF using the TED populated from IGP extensions, then signalled by RSVP-TE; BGP distributes routing reachability, not TE paths. It is tempting because BGP does carry labelled routes in MPLS VPNs, but that is not TE path selection.
Visual reference
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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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
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