300-410 Infrastructure Services Practice Question
A network engineer is configuring MPLS Traffic Engineering (TE) with RSVP-TE on a Cisco IOS XE router. The engineer wants to establish a TE tunnel from Router A to Router D. The path must be explicitly defined to go through Router B and then Router C. The engineer has configured the tunnel interface with the destination and an explicit path. However, the tunnel is not coming up. Which command is required to enable RSVP-TE on the core interfaces of Router A, B, C, and D?
⚠ Common exam trap
The trap here is assuming that enabling MPLS TE globally or configuring the tunnel interface is enough, but RSVP signaling requires explicit interface-level enablement with bandwidth allocation.
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
✓
ip rsvp bandwidth
For RSVP-TE to signal a TE tunnel, RSVP must be enabled on every interface along the path. This is done with the ip rsvp bandwidth command, which also allocates bandwidth for reservations. While global MPLS TE commands and tunnel interface configuration are necessary, they do not activate RSVP on the physical links. The tunnel will remain down if RSVP is not enabled on the core interfaces. Therefore, the correct answer is the interface-level command that enables RSVP and sets the reservable bandwidth.
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 ldp router-id Loopback0 force
Why it's wrong here
MPLS LDP is used for label distribution in the core, but it is separate from RSVP-TE. The command forces LDP to use Loopback0 as the router ID, which is useful for stable LDP sessions, but it does not enable RSVP-TE. In fact, MPLS TE uses RSVP for signaling and can use LDP for label distribution, but the tunnel itself requires RSVP. This command does not enable RSVP on interfaces, so the tunnel still will not come up.
- ✗
mpls traffic-eng tunnels
Why it's wrong here
The mpls traffic-eng tunnels command is a global command that enables MPLS TE tunnel functionality on the router. It is necessary but not sufficient to enable RSVP-TE on interfaces. It allows the router to create and use TE tunnels, but it does not enable RSVP signaling on the physical interfaces. Without interface-level RSVP configuration, the tunnel cannot signal. Therefore, this command alone does not solve the problem.
- ✓
ip rsvp bandwidth
Why this is correct
The ip rsvp bandwidth command must be configured on each core interface that will participate in RSVP-TE. This command enables RSVP on the interface and allocates a percentage or absolute amount of bandwidth for TE reservations. Without it, RSVP messages are not sent or processed on that interface, and the TE tunnel cannot be signaled. Therefore, this is the required interface-level command to enable RSVP-TE on the core links.
- ✗
mpls traffic-eng tunnel-te 1
Why it's wrong here
The mpls traffic-eng tunnel-te 1 command is used to configure a specific TE tunnel interface, but it is not the correct syntax. In Cisco IOS XE, TE tunnel interfaces are created with interface tunnel-te <number>, and then tunnel mode mpls traffic-eng is configured. This command does not exist in that form, and even if it did, it would not enable RSVP on core interfaces. The missing piece is the interface-level RSVP configuration.
Go deeper
Related to this question
Learn chapter
ACL-Based Traffic Filtering and Policy-Based Routing
Key term
LDP Protocol
LDP, or Label Distribution Protocol, is a protocol that routers use to automatically exchange labels that enable MPLS (Multiprotocol Label Switching) to create fast, efficient paths for data packets across a network.
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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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