The answer is that there is no problem; the EIGRP Null0 summary route in the topology table is a normal and expected entry. This route appears because EIGRP automatically installs a local summary route pointing to Null0 whenever a manual summary is configured or when a directly connected network is advertised, using a composite metric of 2560000000/0 to prevent routing loops by discarding packets that match the summary but not a more specific route. On the Cisco CCNP ENARSI 300-410 exam, this output tests your ability to distinguish between a legitimate Null0 route and a problematic black-hole scenario, often appearing as a distractor where candidates mistakenly think the high metric indicates a failure. A common trap is assuming any route with a 2560000000 metric is broken, but remember: a Null0 route with a hop count of 0 and an originating router matching the local router ID is perfectly healthy. Memory tip: “Null0 is normal for summaries—high metric, zero hops, no problem.”
300-410 EIGRP Troubleshooting Practice Question
This 300-410 practice question tests your understanding of eigrp troubleshooting. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "minimum / minimize"
Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
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 route to 10.10.10.0/24 is a local summary or null0 route (via Null0). This is typical for a summary route or a route to a directly connected network. The composite metric of 2560000000/0 indicates a very high metric, which is normal for a null0 route. There is no problem; this is a common configuration.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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
EIGRP automatically installs a null0 route for summary addresses to prevent loops.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
The route has a metric of 2560000000, indicating a network failure.
Why it's wrong here
A high metric for a null0 route is expected and does not indicate failure.
✗
The hop count of 0 means the route is not reachable.
Why it's wrong here
Hop count of 0 is normal for a directly connected or summary route.
✗
The route is in Active state, indicating a problem.
Why it's wrong here
The state is Passive, which is normal.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 300-410 NAT questions on configuration and troubleshooting.
EIGRP Troubleshooting — This question tests EIGRP Troubleshooting — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The route is a local summary route pointing to Null0, which is normal for EIGRP summarization. — The route to 10.10.10.0/24 is a local summary or null0 route (via Null0). This is typical for a summary route or a route to a directly connected network. The composite metric of 2560000000/0 indicates a very high metric, which is normal for a null0 route. There is no problem; this is a common configuration.
What should I do if I get this 300-410 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 300-410 NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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