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 !
interface GigabitEthernet0/2 ip address 10.2.2.1 255.255.255.0
mpls ip !
router ospf 1 network 10.0.0.0 0.255.255.255 area 0
!
router ldp interface GigabitEthernet0/1
! What is the effect of this configuration?
⚠ Common exam trap
Cisco often tests the distinction between 'mpls ip' (which enables MPLS forwarding) and LDP configuration (which controls label distribution adjacencies), trapping candidates who assume that enabling MPLS on an interface automatically activates LDP.
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
✓
LDP will only form an adjacency over GigabitEthernet0/1; no label exchange occurs on GigabitEthernet0/2.
LDP is explicitly enabled only on GigabitEthernet0/1 under the 'router ldp' configuration. Although MPLS IP is enabled on GigabitEthernet0/2, LDP does not automatically form an adjacency or exchange labels on that interface unless it is explicitly configured under the LDP router process. LDP adjacencies are interface-specific and require the 'interface' command under 'router ldp' to be activated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
LDP will only form an adjacency over GigabitEthernet0/1; no label exchange occurs on GigabitEthernet0/2.
Why this is correct
LDP hello messages are multicast on interfaces where LDP is explicitly enabled, typically via the 'mpls ldp' configuration. Because GigabitEthernet0/2 lacks this LDP configuration, it does not participate in LDP neighbor discovery or label binding exchange. Consequently, the LDP adjacency is confined to GigabitEthernet0/1, and only that interface exchanges label mappings; MPLS forwarding may still occur on Gi0/2 using labels learned from other sources, but no dynamic LDP labels are exchanged there.
- ✗
LDP will automatically enable on GigabitEthernet0/2 because MPLS is enabled there.
Why it's wrong here
Enabling 'mpls ip' on an interface only activates MPLS forwarding capabilities, such as label imposition and disposition. LDP is a separate label distribution protocol that must be explicitly activated; it does not automatically start running on an interface just because MPLS is enabled. Without LDP being configured (e.g., via 'mpls ldp' or a specific LDP enable command), no LDP hello messages are sent, so no LDP neighbor relationship forms on that interface.
- ✗
The configuration will fail because LDP must be enabled on all MPLS interfaces.
Why it's wrong here
There is no hard requirement that LDP be enabled on every interface running MPLS. MPLS forwarding can work with label bindings obtained statically, via RSVP-TE, or from other label distribution mechanisms. LDP is only necessary where dynamic label distribution is desired; an interface can be in an MPLS forwarding path without an LDP adjacency, as long as the router knows the appropriate labels from another source.
- ✗
OSPF will automatically enable LDP on all interfaces in area 0.
Why it's wrong here
OSPF is an IP routing protocol that populates the FIB with reachable prefixes; it operates entirely in the IP control plane. LDP is an independent label distribution protocol that uses its own hello mechanism (UDP port 646) to discover neighbors and TCP port 646 for sessions. OSPF has no mechanism to enable or disable LDP, nor does it induce LDP to run on any interface—LDP adjacency formation is solely determined by LDP configuration, not by OSPF area membership or activation.
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
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