CCNA Network Services and Security Practice Question
A company wants internal users to share one public IPv4 address for outbound Internet access, while keeping sessions separate. Which NAT approach best meets that requirement?
⚠ Common exam trap
A common exam trap is selecting static NAT as the solution because it involves address translation, but static NAT only supports one-to-one mappings and cannot handle multiple internal users sharing a single public IP address. Another frequent mistake is assuming private IPv4 addresses can be routed on the Internet without NAT, which is incorrect because private addresses are non-routable externally. Additionally, confusing DHCP relay with NAT functions can mislead candidates, as DHCP relay only forwards DHCP messages and does not perform address translation. Recognizing that PAT overload uniquely enables many-to-one translation with port differentiation is crucial to avoid these pitfalls.
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 overload
PAT is the correct approach because it allows many internal sessions to share one outside IPv4 address while distinguishing them by port numbers. In plain language, PAT gives the office an efficient many-to-one translation model that works well for ordinary user Internet access when public addresses are limited. This is different from static NAT, which gives a fixed one-to-one mapping, and from dynamic NAT pools that usually rely on multiple public addresses. The correct answer is the translation method designed specifically for shared public-address use across many sessions.
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 overload
Why this is correct
PAT overload is the correct method because Port Address Translation (PAT) overload multiplexes thousands of internal private IP addresses through a single public IPv4 address by assigning each session a unique TCP or UDP port number. The router maintains a translation table that maps each internal IP:port combination to the public IP:port, allowing many internal users to share one public IPv4 address simultaneously. This is the standard many-to-one NAT approach used in home and enterprise edge routers.
- ✗
Static NAT only
Why it's wrong here
Static NAT only is wrong because it creates a fixed one-to-one mapping between a single private IPv4 address and a single public IPv4 address. With static NAT, each internal host requires its own dedicated public address, so there is no sharing of one public IP among multiple users. This approach does not fulfill the requirement of allowing many internal users to share a single public IPv4 address.
When this WOULD be correct
In a scenario where a company has a specific requirement to map a single internal server's private IP address to a public IP for hosting a web service, a question might ask for the best NAT approach for that server's fixed IP address. In this case, Static NAT would be the correct choice.
- ✗
No NAT, because private IPv4 addresses are Internet-routable
Why it's wrong here
No NAT is wrong because private IPv4 addresses defined in RFC 1918 (10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16) are explicitly non-routable on the public Internet. Internet routers drop packets that use these source or destination addresses, so internal users cannot directly communicate with external servers without translation. Therefore, NAT is essential to convert private source addresses to a routable public IPv4 address for Internet access.
When this WOULD be correct
In a scenario where a question states that a company is using a private network with a VPN that provides secure access to external resources, and the question asks about the feasibility of direct Internet access, 'No NAT' could be correct if the focus is on the VPN's ability to handle routing without NAT.
- ✗
DHCP relay
Why it's wrong here
DHCP relay is unrelated to address sharing because it simply forwards DHCP broadcast messages from clients on one LAN segment to a DHCP server located on another segment. DHCP relay does not perform any address translation and does not affect how private or public IPv4 addresses are used for Internet connectivity. It is a protocol helper service, not a mechanism for multiplexing many internal users onto one public IPv4 address.
When this WOULD be correct
If the question asked about a scenario where a company needs to manage DHCP requests from multiple subnets without a local DHCP server, then DHCP relay would be the correct answer. This would involve ensuring that clients can obtain IP addresses from a centralized DHCP server located on a different network segment.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓PAT overloadCorrect answer▾
Why this is correct
PAT overload is the correct method because Port Address Translation (PAT) overload multiplexes thousands of internal private IP addresses through a single public IPv4 address by assigning each session a unique TCP or UDP port number. The router maintains a translation table that maps each internal IP:port combination to the public IP:port, allowing many internal users to share one public IPv4 address simultaneously. This is the standard many-to-one NAT approach used in home and enterprise edge routers.
✗Static NAT onlyWrong answer — click to see why▾
Why this is wrong here
Static NAT only maps a single private IP address to a single public IP address, which does not allow multiple internal users to share one public IP for outbound access. This approach does not support session separation for multiple users.
★ When this WOULD be the correct answer
In a scenario where a company has a specific requirement to map a single internal server's private IP address to a public IP for hosting a web service, a question might ask for the best NAT approach for that server's fixed IP address. In this case, Static NAT would be the correct choice.
Why candidates choose this
Candidates may choose this option because they recall that Static NAT is used for IP address mapping, leading them to mistakenly believe it could fulfill the requirement of sharing a public IP for multiple users.
✗No NAT, because private IPv4 addresses are Internet-routableWrong answer — click to see why▾
Why this is wrong here
This option is wrong because private IPv4 addresses are not routable on the Internet; they require NAT to access external networks. Therefore, using no NAT would prevent internal users from reaching the Internet altogether.
★ When this WOULD be the correct answer
In a scenario where a question states that a company is using a private network with a VPN that provides secure access to external resources, and the question asks about the feasibility of direct Internet access, 'No NAT' could be correct if the focus is on the VPN's ability to handle routing without NAT.
Why candidates choose this
Candidates may choose this option due to a misunderstanding of private IP address functionality, believing that private addresses can directly access the Internet without NAT, especially if they recall that private addresses are used in local networks.
✗DHCP relayWrong answer — click to see why▾
Why this is wrong here
DHCP relay is used to forward DHCP requests and responses between clients and servers across different subnets, but it does not provide any NAT functionality. Therefore, it cannot fulfill the requirement of sharing a public IPv4 address for outbound Internet access.
★ When this WOULD be the correct answer
If the question asked about a scenario where a company needs to manage DHCP requests from multiple subnets without a local DHCP server, then DHCP relay would be the correct answer. This would involve ensuring that clients can obtain IP addresses from a centralized DHCP server located on a different network segment.
Why candidates choose this
Candidates may choose this option due to a misunderstanding of DHCP's role in network management, confusing it with NAT functionality, especially in scenarios involving multiple network segments.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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Key term
Dynamic NAT
Dynamic NAT is a method of mapping multiple private IP addresses to a pool of public IP addresses automatically, allowing many devices to share a limited number of public addresses.
Key term
IPv4
IPv4 is the fourth version of the Internet Protocol, a set of rules that assigns unique numerical addresses to devices so they can communicate over networks like the internet.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.