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350-401 Practice Question: Consider the following EIGRP configuration on a…
Consider the following EIGRP configuration on a Cisco IOS router:
router eigrp 100 network 10.0.0.0 passive-interface default no passive-interface GigabitEthernet0/1
What is the effect of this configuration?
⚠ 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 makes all interfaces passive, and the 'no' form selectively activates only the specified interface, rather than the reverse.
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
✓
All interfaces except GigabitEthernet0/1 are passive and will not form EIGRP adjacencies.
The 'passive-interface default' command sets all interfaces to passive by default, preventing them from sending EIGRP hellos and forming adjacencies. The 'no passive-interface GigabitEthernet0/1' command then overrides this default for that specific interface, allowing it to send hellos and form adjacencies. Therefore, only GigabitEthernet0/1 is active for EIGRP neighbor discovery, while all other interfaces remain passive.
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 interfaces except GigabitEthernet0/1 are passive and will not form EIGRP adjacencies.
Why this is correct
The command 'passive-interface default' under EIGRP configuration flips the default behavior so that every interface is passive unless explicitly excluded. A passive interface does not send or process EIGRP hello packets, so it cannot form an adjacency with any neighbor. By then issuing 'no passive-interface GigabitEthernet0/1' (or the equivalent), only that interface remains active and capable of establishing EIGRP neighbors, while all other interfaces stay passive.
- ✗
EIGRP hellos are sent on all interfaces, but GigabitEthernet0/1 is prevented from forming adjacencies.
Why it's wrong here
This option inverts the configuration effect. With 'passive-interface default', EIGRP hellos are not sent on all interfaces; rather, they are suppressed on every interface until an explicit 'no passive-interface' command is applied. Here, only GigabitEthernet0/1 has been reactivated, so Gi0/1 is the one interface where hellos are permitted and adjacencies can form. The other interfaces are the ones prevented from forming adjacencies, not Gi0/1.
- ✗
Only the network 10.0.0.0 is advertised, and all interfaces are passive.
Why it's wrong here
This conflates the EIGRP network statement with passive-interface behavior. The 'network 10.0.0.0' command merely tells EIGRP which directly connected networks to advertise and which interfaces to consider for participation; it has no bearing on passive-interface settings. With 'passive-interface default', all interfaces are passive regardless of the network statement, so even if a loopback or another interface is matched by the network statement, it still will not send hellos unless explicitly enabled. Additionally, 'Only the network 10.0.0.0 is advertised' is not established by the given commands—passive-interface does not modify advertisement.
- ✗
EIGRP will only form adjacencies on interfaces with an IP address in the 10.0.0.0/8 range.
Why it's wrong here
This option misattributes the adjacency behavior to the IP addressing scheme. The passive-interface default command applies to every EIGRP-enabled interface, independent of whether its IP address falls within the 10.0.0.0/8 block. The only interface that can form an adjacency is GigabitEthernet0/1, because it is the sole one with passive mode disabled; other interfaces in the 10.0.0.0/8 range remain passive and will not exchange hellos. Thus, the deciding factor is the interface-specific override, not the network range.
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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