The answer is that the reported distance must be less than the feasible distance. This mandatory condition ensures the alternate path is loop-free because the neighbor’s reported distance represents its own cost to the destination, and if that value is lower than the current successor’s feasible distance, the neighbor cannot be using a path that goes back through the local router. On the Cisco CCNP ENARSI 300-410 exam, this concept tests your understanding of EIGRP’s Diffusing Update Algorithm (DUAL) and its loop-avoidance mechanism; a common trap is confusing reported distance with feasible distance or thinking the feasible distance itself must change. To remember the feasible successor condition, keep this mnemonic: “RD must be less than FD to keep the path loop-free.”
300-410 EIGRP Troubleshooting Practice Question
This 300-410 practice question tests your understanding of eigrp troubleshooting. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
Which of the following is a mandatory condition for a route to be considered a feasible successor in EIGRP?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The reported distance must be less than the feasible distance.
A feasible successor must have a reported distance (RD) less than the feasible distance (FD) of the successor. This ensures the path is loop-free.
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 reported distance must be less than the feasible distance.
Why this is correct
This is the feasibility condition defined by EIGRP.
Related concept
Static NAT maps one inside address to one outside address.
✗
The metric must be equal to the successor's metric.
Why it's wrong here
Equal metrics are not required; the condition is based on reported distance.
✗
The next-hop router must be directly connected.
Why it's wrong here
The next hop must be reachable, but not necessarily directly connected.
✗
The route must be learned from the same AS.
Why it's wrong here
Routes from different ASes are not considered in EIGRP.
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 reported distance must be less than the feasible distance. — A feasible successor must have a reported distance (RD) less than the feasible distance (FD) of the successor. This ensures the path is loop-free.
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.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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