CCNA Network Services and Security Practice Question
Which three of the following statements about Network Address Translation (NAT) are correct? (Choose three.)
⚠ Common exam trap
Cisco often tests the misconception that dynamic NAT provides a fixed mapping like static NAT, or that PAT requires multiple public IPs, when in fact PAT is designed to share a single public IP among many hosts.
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
✓
Static NAT provides a one-to-one mapping between a private IP and a public IP.
Static NAT provides a one-to-one mapping between a private IP and a public IP, ensuring that a specific internal host always uses the same public address. Dynamic NAT uses a pool of public IP addresses assigned on a first-come, first-served basis, so internal hosts compete for available addresses. PAT (Port Address Translation) allows multiple internal hosts to share a single public IP by differentiating sessions via unique port numbers, which is the most common form of NAT used in home and small office routers.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Static NAT provides a one-to-one mapping between a private IP and a public IP.
Why this is correct
Static NAT is a fixed administrative mapping between one inside local (private) address and one inside global (public) address, so traffic initiated toward the public address is translated to the same private host every time. This one-to-one binding is typically used for externally reachable servers, and it remains constant regardless of session state or port number.
- ✓
Dynamic NAT uses a pool of public IP addresses assigned on a first-come, first-served basis.
Why this is correct
Dynamic NAT pulls a public IP address from a configured pool as each outbound flow starts, using a first-come, first-served allocation method. The translated binding is temporary: when the flow times out, the public address is returned to the pool and can later be assigned to a different internal host, making it unpredictable over time.
- ✓
PAT (Port Address Translation) allows multiple internal hosts to share a single public IP address.
Why this is correct
PAT, often called NAT overload, records a protocol and source port along with the private address so many internal hosts can multiplex over a single registered public IP. Because the NAT table tracks each unique combination of private address and source port, a single global IP can support thousands of concurrent TCP or UDP flows.
- ✗
NAT eliminates the need for any routing in a network.
Why it's wrong here
NAT operates only on IP address fields and optionally transport-layer ports; it does not decide which interface or next hop a packet should take. Routers still need a populated routing table, whether built from static routes, dynamic routing protocols, or connected networks, to forward translated packets toward their destination.
- ✗
Dynamic NAT always assigns the same public IP to a given internal host.
Why it's wrong here
Dynamic NAT does not guarantee address consistency; it simply leases the next available public address from a pool for the duration of a translation. Only static NAT binds a host permanently, so an internal host that is dynamically translated may receive a different public IP each time it establishes new traffic.
- ✗
PAT requires a unique public IP for every concurrent session.
Why it's wrong here
PAT deliberately avoids a one-public-IP-per-host requirement by using the source port as an additional identifier, allowing many hosts to share a single public address. Each concurrent session still gets a unique translation entry, but that uniqueness is based on the port mapping, not on owning a distinct public IP address.
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Key term
NAT
NAT (Network Address Translation) is a method that allows multiple devices on a private network to share a single public IP address when accessing the internet.
Key term
Port Address Translation
A networking technique that maps multiple private IP addresses and their ports to a single public IP address using unique port numbers.
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