The answer is that ICMP NAT entries timeout after 60 seconds by default. This is correct because Cisco IOS NAT treats ICMP query messages, such as echo requests and replies, by using the ICMP identifier field as a pseudo-port to track the translation, similar to how it handles UDP or TCP sessions. The default timeout of 60 seconds is specifically designed for these ICMP flows, which are inherently short-lived compared to other protocols. On the Cisco CCNP ENARSI 300-410 exam, this concept tests your understanding of NAT behavior beyond basic TCP and UDP translations, often appearing as a distractor where candidates mistakenly assume ICMP uses the same timeout as UDP (5 minutes) or TCP (24 hours). A common trap is forgetting that ICMP does not have real ports, so NAT relies on the identifier, and the 60-second timeout is a key differentiator. To remember, think “ICMP pings are quick—60 seconds and they’re gone.”
300-410 NAT and PAT Practice Question
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 true regarding the default behavior of NAT in Cisco IOS when handling ICMP traffic?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
ICMP NAT entries timeout after 60 seconds by default.
Cisco IOS NAT translates ICMP traffic by default. ICMP query types (such as echo request/reply) are translated using the ICMP identifier field as a pseudo-port, and the default timeout for ICMP NAT entries is 60 seconds.
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.
✗
ICMP traffic is not translated by NAT unless explicitly configured.
ICMP NAT entries use the same timeout as TCP entries by default.
Why it's wrong here
ICMPNAT entries have a default timeout of 60 seconds, not 86400.
✓
ICMP NAT entries timeout after 60 seconds by default.
Why this is correct
Correct. The default timeout for ICMPNAT entries is 60 seconds in Cisco IOS.
Related concept
Static NAT maps one inside address to one outside address.
✗
ICMP NAT entries are permanent and do not time out.
Why it's wrong here
ICMPNAT entries are dynamic and time out after 60 seconds.
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.
NAT and PAT — This question tests NAT and PAT — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: ICMP NAT entries timeout after 60 seconds by default. — Cisco IOS NAT translates ICMP traffic by default. ICMP query types (such as echo request/reply) are translated using the ICMP identifier field as a pseudo-port, and the default timeout for ICMP NAT entries is 60 seconds.
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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