hardMultiple Choice
300-410 Practice Question: Runs the following command on Router R1: R1# show…
A network engineer runs the following command on Router R1:
R1# show ip eigrp topology 10.10.10.0/24
EIGRP-IPv4 Topology Entry for AS(100)/ID(192.168.1.1) for 10.10.10.0/24 State: Passive, Reply status: 0, Originating router: 192.168.1.1 Routing Descriptor Blocks:
0.0.0.0 (Null0) from 0.0.0.0, Send flag: 0x0
Composite metric: (2560000000/0), Route is Internal Vector metric: Minimum bandwidth: 100000 Kbit Total delay: 100 microseconds Reliability: 255/255 Load: 1/255 Minimum MTU: 1500 Hop count: 0
Based on this output, what is the problem?
⚠ Common exam trap
Cisco often tests the misconception that a Null0 route or a high metric indicates a failure, when in fact it is a normal and necessary part of EIGRP summarization to prevent black holes.
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 route is a local summary route pointing to Null0, which is normal for EIGRP summarization.
The output shows a Null0 summary route in EIGRP, which is normal when manual summarization is configured. The route is in Passive state with a composite metric of 2560000000/0, indicating it is a local summary route installed to prevent routing loops. This is expected behavior, not a problem.
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 route is a local summary route pointing to Null0, which is normal for EIGRP summarization.
Why this is correct
The Null0 entry with hop count 0 and no next hop is EIGRP's automatic summary route for 10.10.10.0/24, generated locally on the originating router. It is expected behaviour, not a fault, so no adjacency or metric problem exists here.
- ✗
The route has a metric of 2560000000, indicating a network failure.
Why it's wrong here
The 2560000000 metric is the maximum EIGRP metric, but it accompanies a Null0 summary route originated locally, not a failure. It is tempting because unreachable routes often show maximum metrics, yet here the Passive state and Null0 next hop confirm a valid summary, so the metric alone signals nothing.
- ✗
The hop count of 0 means the route is not reachable.
Why it's wrong here
A hop count of zero is normal for a locally originated route, including a Null0 summary, and does not indicate unreachability. It is tempting because zero hops suggests no path, but EIGRP reports zero for routes the router itself originates, so reachability is unaffected.
- ✗
The route is in Active state, indicating a problem.
Why it's wrong here
The output explicitly shows State: Passive, meaning the route is settled and not awaiting replies; Active state would indicate a stuck query. It is tempting because Active state genuinely signals EIGRP convergence trouble, but here the state is Passive, so no such problem exists.
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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