mediumMultiple Choice
350-401 Practice Question: Router R6 has the following OSPF configuration:…
Router R6 has the following OSPF configuration: router ospf 1
router-id 6.6.6.6
network 192.168.0.0 0.0.255.255 area 0 passive-interface default no passive-interface GigabitEthernet0/0
!
interface GigabitEthernet0/0 ip address 192.168.1.6 255.255.255.0 ip ospf 1 area 0
What is the effect of the 'passive-interface default' command?
⚠ Common exam trap
Cisco often tests the interaction between 'passive-interface default' and 'no passive-interface' to see if candidates understand that the default command applies to all interfaces and must be explicitly overridden per interface, rather than assuming the 'network' command alone controls adjacency formation.
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
✓
Only GigabitEthernet0/0 is active; all other OSPF interfaces are passive.
The 'passive-interface default' command sets all OSPF interfaces to passive by default, meaning they will not send or receive OSPF hello packets and thus cannot form adjacencies. The subsequent 'no passive-interface GigabitEthernet0/0' overrides this for that specific interface, making it the only active OSPF interface. This matches option B.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
All OSPF interfaces become passive, including GigabitEthernet0/0.
Why it's wrong here
Under passive-interface default, all OSPF interfaces initially suppress hello packets and cannot form neighbor relationships. However, the explicit no passive-interface GigabitEthernet0/0 command re-enables hello processing on that interface, so Gi0/0 is not passive. Therefore, this option is incorrect because it ignores the override that makes Gi0/0 active.
- ✓
Only GigabitEthernet0/0 is active; all other OSPF interfaces are passive.
Why this is correct
The passive-interface default directive makes every OSPF-enabled interface passive unless a specific interface is later excluded. The no passive-interface GigabitEthernet0/0 command removes that default for Gi0/0, permitting OSPF hello packets and adjacency formation on that link. All other OSPF interfaces remain passive and silent, so only GigabitEthernet0/0 is active in OSPF terms. This precisely matches the configuration, making it the correct answer.
- ✗
OSPF adjacencies are formed on all interfaces.
Why it's wrong here
Passive interfaces in OSPF do not transmit or listen for hello packets, which are required to discover neighbors and establish adjacencies. Since only GigabitEthernet0/0 has the passive state overridden, neighbor discovery is possible only there. All other interfaces, still passive, will not send hellos and thus cannot form OSPF adjacencies; therefore, the claim that adjacencies form on all interfaces is false.
- ✗
The 'passive-interface default' command is ignored because the 'network' command is used.
Why it's wrong here
The network command merely selects which interfaces participate in OSPF by matching an address range, while the passive-interface command controls whether a selected interface actively sends hello packets. These two functions are independent: passive-interface default remains in force even when a network statement covers an interface. The only way to change the passive state is a matching no passive-interface statement, so the default is never ignored.
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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