- A
NAT cannot translate UDP traffic.
Why wrong: NAT can translate UDP traffic using PAT.
- B
NAT is incompatible with TCP traffic.
Why wrong: NAT works with TCP traffic.
- C
NAT breaks end-to-end IP connectivity and can interfere with application-layer protocols.
Correct. This is a well-known limitation of NAT as per RFC 2663.
- D
NAT requires all traffic to be encrypted.
Why wrong: NAT does not require encryption.
Question 1,185 of 2,152
NAT Limitations — RFC 2663 Breaks End-to-End IP Connectivity | Cisco CCNP ENARSI 300-410 Explained
This 300-410 practice question tests your understanding of nat and pat. 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 limitation of NAT as defined in RFC 2663?
Quick Answer
The correct choice is that NAT breaks end-to-end IP connectivity and can interfere with application-layer protocols, as defined in RFC 2663. This limitation arises because NAT modifies IP addresses and port numbers in the packet header, which violates the fundamental Internet design principle that every host should be directly reachable by its IP address. Protocols like FTP or SIP embed IP addresses inside their payload, so when NAT changes the source address without updating those embedded references, the connection fails or behaves unpredictably. On the Cisco CCNP ENARSI 300-410 exam, this concept tests your understanding of NAT’s architectural trade-offs, often appearing in questions about application layer gateway (ALG) requirements or scenarios where VoIP or active FTP breaks after translation. A common trap is assuming NAT only affects routing, not upper-layer protocols. Remember the mnemonic: “NAT breaks the end-to-end path, and payload IPs feel the wrath.”
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
✓
NAT breaks end-to-end IP connectivity and can interfere with application-layer protocols.
RFC 2663 defines NAT as a mechanism that modifies IP addresses and/or ports in packet headers, which inherently breaks the end-to-end IP connectivity model. This modification can interfere with application-layer protocols that embed IP addresses or port numbers in their payload, such as FTP, SIP, or DNS, because NAT does not automatically translate these embedded addresses.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
NAT cannot translate UDP traffic.
- ✗
NAT is incompatible with TCP traffic.
- ✓
NAT breaks end-to-end IP connectivity and can interfere with application-layer protocols.
Why this is correct
Correct. This is a well-known limitation of NAT as per RFC 2663.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
NAT requires all traffic to be encrypted.
Why it's wrong here
NAT does not require encryption.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that NAT is transparent to all traffic, when in fact it breaks end-to-end connectivity and requires ALGs for protocols that embed addressing information in the payload.
Detailed technical explanation
How to think about this question
Under the hood, NAT maintains a translation table mapping internal private IP:port pairs to external public IP:port pairs. For application-layer protocols like FTP, the PORT command embeds the private IP address in the payload, which NAT must intercept and rewrite via an Application Layer Gateway (ALG); without an ALG, the connection fails. In real-world scenarios, this is why FTP in active mode often breaks when traversing a NAT device without proper ALG support.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Visual reference
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this 300-410 question test?
NAT and PAT — This question tests NAT and PAT — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: NAT breaks end-to-end IP connectivity and can interfere with application-layer protocols. — RFC 2663 defines NAT as a mechanism that modifies IP addresses and/or ports in packet headers, which inherently breaks the end-to-end IP connectivity model. This modification can interfere with application-layer protocols that embed IP addresses or port numbers in their payload, such as FTP, SIP, or DNS, because NAT does not automatically translate these embedded addresses.
What should I do if I get this 300-410 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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