350-501 Architecture Practice Question
Exhibit
Refer to the exhibit. interface GigabitEthernet0/0 ip address 10.0.0.1 255.255.255.252 mpls ip mpls mtu 1500 ! interface GigabitEthernet0/1 ip address 10.0.0.5 255.255.255.252 mpls ip mpls mtu 1500 ! router ospf 1 network 10.0.0.0 0.0.0.3 area 0 network 10.0.0.4 0.0.0.3 area 0 ! mpls ldp router-id Loopback0 force ! mpls label range 100 199 ! mpls label protocol ldp
Refer to the exhibit. An engineer configures MPLS LDP on a router. The router has two interfaces with IP addresses 10.0.0.1/30 and 10.0.0.5/30. The engineer notices that LDP sessions are not established. The OSPF neighbor adjacencies are up. What is the most likely cause?
⚠ Common exam trap
Cisco often tests the distinction between global LDP configuration and interface-level activation, leading candidates to assume that enabling LDP globally is sufficient for session establishment.
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 is not enabled on the interfaces
D is correct because MPLS LDP requires explicit interface-level activation under the `mpls ip` command. Even if OSPF adjacencies are up and the global LDP process is configured, LDP will not form sessions on interfaces where `mpls ip` is missing. The engineer likely enabled LDP globally but forgot to enable it on the specific interfaces, which is a common oversight.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The OSPF network statements do not cover the interfaces correctly
Why it's wrong here
OSPF network statements are used to advertise interfaces into OSPF. Since OSPF adjacencies are up, the interfaces are correctly covered. This is not the cause of LDP session failure.
- ✗
The MPLS MTU is set to 1500, which is too low
Why it's wrong here
MPLS MTU of 1500 is standard and should not prevent LDP sessions. LDP uses UDP (discovery) and TCP (session) which do not require a specific MTU.
- ✗
The label range is too small
Why it's wrong here
The label range (typically 16-1048575) is sufficiently large even for many labels. A small label range would not prevent LDP session establishment; it would only impact label allocation.
- ✓
LDP is not enabled on the interfaces
Why this is correct
Correct. LDP requires explicit interface-level activation using the `mpls ip` command. Even if LDP is enabled globally, sessions will not form on interfaces where `mpls ip` is missing.
Visual reference
Go deeper
Related to this question
About these practice questions
Courseiva writes every 350-501 question from scratch — 971 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or dumps. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-501 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 350-501 exam.