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Which NAT feature allows many inside hosts to share one public IPv4 address by using unique source port numbers?

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Which NAT feature allows many inside hosts to share one public IPv4 address by using unique source port numbers?

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Answer choices

Why each option matters

Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.

A

Distractor review

Static NAT

Static NAT is a fixed one-to-one mapping.

B

Best answer

PAT

PAT uses port numbers to multiplex many inside devices to one or a few public addresses.

C

Distractor review

NTP authentication

That is unrelated to address translation.

D

Distractor review

Port security

Port security controls MAC addresses on switch ports.

Common exam trap

Common exam trap: answer the scenario, not the keyword

A common exam trap is mistaking Static NAT for PAT. Static NAT creates a fixed one-to-one mapping between inside and outside IP addresses without using port numbers, so it cannot support multiple hosts sharing one public IP. Another trap is confusing unrelated features like NTP authentication or port security with NAT functions. NTP authentication secures time synchronization and port security restricts MAC addresses on switch ports; neither involves IP address translation or port multiplexing. Candidates who overlook the role of Layer 4 port numbers in PAT may incorrectly select these options, missing the key concept that PAT uniquely identifies sessions by port numbers to allow many hosts to share a single public IPv4 address.

Technical deep dive

How to think about this question

Network Address Translation (NAT) is a fundamental technology in IPv4 networking that allows private IP addresses to be translated into public IP addresses for communication over the internet. Port Address Translation (PAT), a specialized form of NAT, enables multiple inside hosts to share a single public IPv4 address by differentiating each session using unique source port numbers. This multiplexing allows many devices behind a NAT device to communicate externally without requiring a unique public IP address for each device. PAT operates by modifying both the source IP address and the source port number of outgoing packets. When an inside host initiates a connection, PAT assigns a unique source port number to that session and records this mapping in a translation table. Incoming return traffic is then matched to the correct inside host based on the destination port and IP address. This process is often called NAT overload because it overloads a single public IP address with many port mappings, maximizing the efficient use of scarce IPv4 addresses. A common exam trap is confusing PAT with Static NAT or other unrelated features like NTP authentication or port security. Static NAT provides a one-to-one mapping and does not use port numbers to multiplex connections. Understanding PAT’s use of Layer 4 port numbers to distinguish sessions is critical for Cisco CCNA exams. In practical networks, PAT is widely deployed in home routers and enterprise edge devices to conserve public IP addresses while maintaining connectivity for multiple internal hosts.

KKey Concepts to Remember

  • PAT allows multiple inside hosts to share a single public IPv4 address by assigning unique source port numbers to each session.
  • PAT operates by translating both the source IP address and source port number, enabling multiplexing of many private IP addresses onto one public IP address.
  • Static NAT provides a fixed one-to-one mapping between private and public IP addresses and does not use port numbers for multiplexing.
  • NTP authentication is unrelated to NAT and deals with securing time synchronization protocols.
  • Port security controls MAC address access on switch ports and does not perform IP address translation or port multiplexing.
  • PAT maintains a translation table that tracks inside local IP addresses and ports to outside global IP addresses and ports for proper packet forwarding.
  • Cisco devices implement PAT as NAT overload, which is essential for conserving IPv4 addresses in networks with many hosts.
  • Understanding PAT’s use of Layer 4 port numbers is critical to correctly answering NAT-related questions on the CCNA exam.

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.

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More questions from this exam

Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.

Question 1

A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?

Question 2

A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?

Question 3

What is the OSPF metric called?

Question 4

A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?

Question 5

A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?

Question 6

A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?

FAQ

Questions learners often ask

What does this 200-301 question test?

PAT allows multiple inside hosts to share a single public IPv4 address by assigning unique source port numbers to each session.

What is the correct answer to this question?

The correct answer is: PAT — PAT, sometimes called NAT overload, keeps track of connections by using Layer 4 port numbers so many private hosts can share a single public address.

What should I do if I get this 200-301 question wrong?

Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.

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