mediumMultiple Choice
CCNP Practice Question: Router R5 has the following OSPF configuration:…
Router R5 has the following OSPF configuration: router ospf 1
router-id 5.5.5.5
network 10.0.0.0 0.255.255.255 area 0 area 0 authentication message-digest
!
interface GigabitEthernet0/0 ip address 10.1.1.5 255.255.255.0 ip ospf message-digest-key 1 md5 cisco123
What is missing from this OSPF authentication configuration?
⚠ Common exam trap
Many candidates assume configuring the area authentication and the key is sufficient, overlooking the mandatory interface-level `ip ospf authentication message-digest` command that activates authentication on the specific interface.
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
✓
The interface needs the 'ip ospf authentication message-digest' command.
OSPF authentication configuration requires two components: an area-level authentication type (configured via `area 0 authentication message-digest`) and an interface-level authentication mode (configured via `ip ospf authentication message-digest`). The interface command tells the OSPF process to actually use the key defined with `ip ospf message-digest-key`. Without it, the interface defaults to no authentication, even though the area is configured for authentication.
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 configuration is complete and correct.
Why it's wrong here
The interface lacks the ip ospf authentication message-digest command, so no MD5 digest is sent on GigabitEthernet0/0 despite the area-level setting and configured key. Area authentication alone does not enable interface authentication. The configuration looks complete because the key exists, which tempts candidates; the interface command is the actual requirement.
- ✓
The interface needs the 'ip ospf authentication message-digest' command.
Why this is correct
Area 0 already enables MD5 authentication, but the interface itself lacks the enabling command, so no digest is sent. Adding 'ip ospf authentication message-digest' on GigabitEthernet0/0 activates authentication, allowing the configured key 1 to be used.
- ✗
The 'area 0 authentication' command should be 'area 0 authentication md5'.
Why it's wrong here
Cisco IOS syntax is 'area 0 authentication message-digest'; 'area 0 authentication md5' is not a valid keyword combination and would be rejected. It is tempting because MD5 is the hashing algorithm in use, but the parser expects 'message-digest', and the real omission is the interface-level authentication command.
- ✗
The 'network' command should include the area authentication keyword.
Why it's wrong here
The 'network' command only advertises prefixes into an area; it carries no authentication parameters, so appending a keyword there is syntactically invalid. It is tempting because area-wide settings are configured under 'router ospf', but authentication mode is set with 'area 0 authentication message-digest' and the interface command.
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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JA
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.