mediumMultiple Choice
350-401 Practice Question: Interface GigabitEthernet0/1 ip address 10.1.1.1…
interface GigabitEthernet0/1 ip address 10.1.1.1 255.255.255.0
mpls ip mpls label protocol ldp !
router ospf 1 network 10.1.1.0 0.0.0.255 area 0
!
router ldp interface GigabitEthernet0/1
! What is the effect of this configuration?
⚠ Common exam trap
Cisco often tests the misconception that LDP only labels OSPF or IGP routes, when in fact LDP distributes labels for all routes in the routing table by default, including static and connected routes.
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 is enabled on GigabitEthernet0/1, and LDP will distribute labels for all routes in the routing table.
The `mpls ip` command under the interface enables MPLS forwarding, and the `router ldp` configuration with the interface specified activates LDP on that interface. LDP will then distribute labels for all routes in the routing table (including OSPF, static, connected, etc.) by default, as LDP does not filter based on routing protocol. The `mpls label protocol ldp` command is indeed redundant since LDP is the default label distribution protocol in Cisco IOS, but it does not break the configuration.
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 is enabled on GigabitEthernet0/1, and LDP will distribute labels for all routes in the routing table.
Why this is correct
The `mpls ip` command on GigabitEthernet0/1 enables MPLS frame-mode switching on that interface, and because `mpls label protocol ldp` is set, LDP runs on that interface. By default, LDP advertises a label for every IPv4 prefix in the routing table, regardless of whether the route was learned via OSPF, configured as static, or directly connected. Therefore, the statement that all routing-table routes receive labels is correct.
- ✗
Only OSPF routes are labeled; static routes are excluded from LDP label distribution.
Why it's wrong here
This option misstates LDP's label advertisement behavior: by default, LDP creates label bindings for all routes in the routing table, not just those from OSPF. Static and directly connected routes also receive labels unless a route-map or an `mpls ldp label` filter explicitly restricts which prefixes are bound. Therefore, excluding static routes from LDP label distribution is not a default characteristic.
- ✗
The 'mpls label protocol ldp' command is redundant because LDP is the default.
Why it's wrong here
The `mpls label protocol ldp` command is not truly redundant even if LDP is the default in many IOS versions. It explicitly selects LDP as the label distribution protocol and eliminates ambiguity, especially when TDP or another protocol was previously configured or when the system is being migrated from an older MPLS implementation. Thus, this command provides deterministic behavior and is a meaningful configuration line, not a no-op.
- ✗
The configuration will fail because 'router ldp' requires an LDP router-id to be set.
Why it's wrong here
A missing LDP router-id command will not cause the configuration to fail. LDP automatically selects its router-id by choosing the highest IPv4 address configured on a loopback interface, or if no loopback exists, the highest IPv4 address on any active interface. The `router ldp` command simply enters LDP configuration mode and has no hard dependency on an explicitly configured router-id being present.
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 by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.