- A
It translates the source IP address of packets arriving on an interface configured as 'ip nat outside'.
Correct. The command translates the source address of outside-originated traffic.
- B
It can be used to map an external public IP to an internal private IP so that inside routers can route to the private address.
Correct. This is a common use case, e.g., when an external server's IP must appear as a private address inside the network.
- C
It requires the 'overload' keyword to perform Port Address Translation.
Why wrong: Incorrect. 'overload' is used with 'ip nat inside source' for PAT; 'ip nat outside source' does not use overload.
- D
It translates the destination IP address of packets leaving the inside network.
Why wrong: Incorrect. 'ip nat outside source' translates source IPs of outside packets, not destination IPs of inside packets.
- E
The translation is unidirectional; return traffic is not translated back.
Why wrong: Incorrect. NAT is bidirectional; the router automatically performs reverse translation for return traffic.
ip nat outside source — Translating External Source IPs | Cisco CCNP ENARSI 300-410 Explained
This 300-410 practice question tests your understanding of nat and pat. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 TWO statements about the 'ip nat outside source' feature are true? (Choose TWO.)
Quick Answer
The correct answer is that the ip nat outside source feature can be used to map an external public IP to an internal private IP so that inside routers can route to the private address. This works because the command translates the source IP of packets entering from the outside network, effectively allowing an internal router to see a routable private destination instead of an unreachable public address. On the Cisco CCNP ENARSI 300-410 exam, this concept tests your understanding of NAT asymmetry—specifically, how outside source translation differs from the more common inside source NAT. A common trap is confusing it with destination NAT or assuming it requires the overload keyword for PAT, but ip nat outside source is strictly a one-to-one, bidirectional mapping that does not alter destination IPs. Remember the memory tip: "Outside source changes the source of the outsider," meaning it tweaks the IP of the external host so internal devices can reply.
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
It translates the source IP address of packets arriving on an interface configured as 'ip nat outside'.
Option A is correct because the 'ip nat outside source' command translates the source IP address of packets that arrive on an interface configured as 'ip nat outside'. This is used when an external host's source address needs to be translated to a different address, typically to allow inside routers to route return traffic to a private address that the external host is mapped to.
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.
- ✓
It translates the source IP address of packets arriving on an interface configured as 'ip nat outside'.
Why this is correct
Correct. The command translates the source address of outside-originated traffic.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
It can be used to map an external public IP to an internal private IP so that inside routers can route to the private address.
Why this is correct
Correct. This is a common use case, e.g., when an external server's IP must appear as a private address inside the network.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
It requires the 'overload' keyword to perform Port Address Translation.
- ✗
It translates the destination IP address of packets leaving the inside network.
- ✗
The translation is unidirectional; return traffic is not translated back.
Why it's wrong here
Incorrect. NAT is bidirectional; the router automatically performs reverse translation for return traffic.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between 'ip nat inside source' and 'ip nat outside source', and candidates mistakenly assume that 'outside source' translates destination addresses or that translations are unidirectional.
Detailed technical explanation
How to think about this question
Under the hood, 'ip nat outside source' creates a NAT translation entry that maps an external source IP to an internal (private) IP. When a packet arrives on the outside interface, the source IP is replaced with the mapped private address, and the router maintains a stateful translation table so that return traffic from the inside network has its destination IP translated back to the original external address. This is commonly used in overlapping network scenarios or when an external server must appear reachable via a private address for routing purposes.
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
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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: It translates the source IP address of packets arriving on an interface configured as 'ip nat outside'. — Option A is correct because the 'ip nat outside source' command translates the source IP address of packets that arrive on an interface configured as 'ip nat outside'. This is used when an external host's source address needs to be translated to a different address, typically to allow inside routers to route return traffic to a private address that the external host is mapped to.
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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