mediumMultiple Select
300-410 Practice Question: Which TWO configuration steps are required to…
Which TWO configuration steps are required to enable MPLS on a Cisco IOS-XE router using LDP? (Choose TWO.)
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
✓
Configure 'mpls ip' on the desired interfaces.
To enable MPLS with LDP, you must configure 'mpls ip' on the interface and also enable a routing protocol (like OSPF or IS-IS) to provide reachability. The 'mpls label protocol ldp' command is optional as LDP is the default, and 'mpls ldp router-id' is optional. 'mpls forwarding-table' is not a configuration command.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Configure 'mpls ip' on the desired interfaces.
Why this is correct
Enabling 'mpls ip' on an interface activates LDP on that link, triggering label exchange with the adjacent LSR. This is the interface-level step that actually turns on MPLS forwarding and LDP advertisement, satisfying the requirement to enable MPLS on the router's participating links.
- ✗
Configure 'mpls label protocol ldp' globally.
Why it's wrong here
'mpls label protocol ldp' is the default on IOS-XE and configures nothing unless 'mpls ip' is enabled per interface; the required steps are global 'mpls ip' plus interface-level 'mpls ip'. It tempts because it names LDP explicitly, and it would matter only when overriding a non-default label protocol such as TDP.
- ✓
Configure a routing protocol (e.g., OSPF) to provide IGP reachability between LSRs.
Why this is correct
LDP relies on the IGP to learn loopback addresses of remote LSRs, so OSPF (or IS-IS) must advertise those prefixes before label-switched paths can form. Without this reachability, LDP sessions cannot establish end-to-end across the MPLS domain, making IGP configuration a prerequisite alongside interface-level MPLS.
- ✗
Configure 'mpls forwarding-table' to allocate labels.
Why it's wrong here
The 'mpls forwarding-table' command only tunes LFIB behaviour and allocates no labels; LDP label allocation is driven by 'mpls ip' on interfaces plus the global 'mpls label protocol ldp'. It tempts because forwarding-table settings do exist for MPLS troubleshooting, but they presuppose LDP is already running.
- ✗
Configure 'mpls ldp router-id' to set the LDP router ID.
Why it's wrong here
The LDP router ID is derived automatically from the highest loopback or interface address, so this command is optional and not required to enable LDP. It is tempting because explicitly setting a stable router ID is good practise in multi-protocol environments, and the command exists.
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.
Go deeper
Related to this question
Learn chapter
ACL-Based Traffic Filtering and Policy-Based Routing
Key term
MPLS Label Distribution
MPLS Label Distribution is the process by which routers exchange labels that tell them how to forward packets across a network without looking at the IP address each time.
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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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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