Question 975 of 2,152

NAT and PAT →hardMultiple SelectObjective-mapped

PAT Overload Behavior — Cisco IOS Commands and NAT Table Fields | 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 THREE statements about NAT and PAT behavior in Cisco IOS are true? (Choose THREE.)

A
PAT allows multiple inside hosts to share a single public IP address by using unique source port numbers.
Correct. PAT multiplexes many inside addresses to one outside address by differentiating TCP/UDP ports.
B
The NAT translation table for PAT includes the inside global IP and port, and the outside global IP and port.
Correct. The full entry includes inside local, inside global, outside local, and outside global addresses and ports.
C
The command 'ip nat inside source list 1 interface GigabitEthernet0/0 overload' enables PAT using the interface IP.
Correct. This is the standard command for PAT where the interface IP is used as the inside global address.
D
The 'ip nat inside source static' command automatically enables PAT when multiple inside hosts are configured.
Why wrong: Incorrect. Static NAT creates a one-to-one mapping and does not use PAT; each inside host requires a separate public IP.
E
The 'ip nat pool' command is required for all PAT configurations.
Why wrong: Incorrect. PAT can use a single interface IP without a pool; a pool is only needed when using a range of addresses.

Full breakdown with real-world context →

Quick Answer

The correct answer identifies that the command 'ip nat inside source list 1 interface GigabitEthernet0/0 overload' enables PAT using the interface IP. This is because PAT overload behavior in Cisco IOS relies on unique port numbers to multiplex multiple inside hosts behind a single public IP address, with the NAT table storing a five-tuple mapping—protocol, inside local IP:port, inside global IP:port, outside local IP:port, and outside global IP:port—to track each session. On the Cisco CCNP ENARSI 300-410 exam, this tests your ability to distinguish PAT from static NAT or dynamic NAT with a pool, as the overload keyword is the key differentiator; a common trap is confusing 'ip nat inside source static' (which creates a one-to-one mapping without overload) or assuming a pool is required when PAT can use a single interface IP. Remember the mnemonic "POINT" for the five NAT table fields: Protocol, Outside, Inside, Next-hop, and Translation—or simply recall that overload means port multiplexing on one IP.

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

✓

PAT allows multiple inside hosts to share a single public IP address by using unique source port numbers.

Option A is correct because PAT (Port Address Translation) extends NAT by using unique source port numbers to multiplex multiple inside hosts over a single public IP address. This allows many internal devices to share one external IP, with the router tracking each session by the combination of inside global IP and port.

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.

✓
PAT allows multiple inside hosts to share a single public IP address by using unique source port numbers.
Why this is correct
Correct. PAT multiplexes many inside addresses to one outside address by differentiating TCP/UDP ports.
Related concept
Read the scenario before looking for a memorised answer.
✓
The NAT translation table for PAT includes the inside global IP and port, and the outside global IP and port.
Why this is correct
Correct. The full entry includes inside local, inside global, outside local, and outside global addresses and ports.
Related concept
Read the scenario before looking for a memorised answer.
✓
The command 'ip nat inside source list 1 interface GigabitEthernet0/0 overload' enables PAT using the interface IP.
Why this is correct
Correct. This is the standard command for PAT where the interface IP is used as the inside global address.
Related concept
Read the scenario before looking for a memorised answer.
✗
The 'ip nat inside source static' command automatically enables PAT when multiple inside hosts are configured.
Why it's wrong here
Incorrect. Static NAT creates a one-to-one mapping and does not use PAT; each inside host requires a separate public IP.
✗
The 'ip nat pool' command is required for all PAT configurations.
Why it's wrong here
Incorrect. PAT can use a single interface IP without a pool; a pool is only needed when using a range of addresses.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the distinction between static NAT and PAT, where candidates mistakenly think 'ip nat inside source static' can automatically perform PAT, but it only creates a fixed one-to-one mapping without port multiplexing.

Detailed technical explanation

How to think about this question

PAT, also known as NAT overload, modifies the Layer 4 source port in addition to the IP address, allowing up to 65,536 simultaneous sessions per public IP (theoretically, though limited by memory and port ranges). The NAT translation table for PAT includes the inside global IP:port and outside global IP:port, enabling the router to demultiplex return traffic correctly. In Cisco IOS, the 'overload' keyword is what triggers PAT behavior, and it can be applied either to a pool or directly to an interface IP.

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: PAT allows multiple inside hosts to share a single public IP address by using unique source port numbers. — Option A is correct because PAT (Port Address Translation) extends NAT by using unique source port numbers to multiplex multiple inside hosts over a single public IP address. This allows many internal devices to share one external IP, with the router tracking each session by the combination of inside global IP and port.

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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Same concept, more angles

1 more ways this is tested on 300-410

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. Which TWO statements about NAT overload (PAT) are true? (Choose TWO.)

medium

✓ A.PAT allows multiple inside hosts to share a single public IP address by using unique source port numbers.
B.PAT is only supported with a single public IP address configured on the outside interface.
✓ C.PAT is also known as NAT overload and is defined in RFC 2663.
D.PAT cannot translate traffic for protocols that use static port numbers, such as DNS or HTTP.
E.PAT requires the ip nat inside source list command with the overload keyword.

Why A: A is correct because PAT (Port Address Translation) allows multiple internal hosts to share a single public IP address by assigning unique source port numbers to each session. This multiplexing technique enables many concurrent connections from different inside hosts to appear as if they originate from the same public IP, with the NAT device tracking each session by the combination of source IP and source port.

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