Which type of NAT permanently maps a specific internal IP address to a specific public IP address so that the same external address is always used for that internal host?
Correct Answer: B
Detailed Explanation: Network Address Translation (NAT) is a technique that allows private IP addresses to be translated to public IP addresses so that hosts within a private network can communicate with external networks (and vice versa). There are several forms of NAT, each with different characteristics and use cases. The primary types include static NAT, dynamic NAT, and Port Address Translation (PAT), sometimes called NAT overload. Static NAT establishes a fixed, one-to-one mapping between a private (internal) IP address and a public (external) IP address. This mapping is manually configured and remains constant, meaning that every time the internal host communicates with the external network, it will always use the same public IP address. This is particularly useful for devices that require consistent external reachability, such as web servers, mail servers, or other resources that need to be accessed by external users. Because the mapping does not change, it provides a predictable translation that is crucial for services that rely on a consistent IP endpoint. In contrast, dynamic NAT uses a pool of public IP addresses and dynamically assigns an available public address to an internal host when it initiates a session. The mapping is temporary and can change with each session. While dynamic NAT conserves public IP addresses by reusing them among many hosts, it does not guarantee that an internal host will always use the same external address. This variability is acceptable for most outbound traffic from client devices but is not suitable for servers that must be consistently reachable. Port Address Translation (PAT), often known as NAT overload, allows multiple internal hosts to share a single public IP address by differentiating sessions based on port numbers. Although this conserves public addresses even further, it is mainly used for outbound client sessions where incoming connections are not expected on the same IP. The question asks specifically which NAT type “permanently maps” an internal IP to an external IP. Static NAT fits this description exactly, as it creates a permanent one-to-one association, ensuring that the internal host always appears with the same public address. Key Considerations: Use Case: Static NAT is ideal for servers and resources requiring predictable, constant external reachability. Configuration: Since static NAT mappings are manually configured, they are less scalable in large networks compared to dynamic NAT or PAT, but they offer the consistency needed for certain applications. Security: With static NAT, administrators must ensure that the public IP is appropriately secured, as it consistently exposes the internal host to external networks. Conclusion: Because static NAT creates a fixed mapping between an internal and a public IP address, Option B is the correct answer. Understanding the differences between static, dynamic, and PAT is essential for choosing the right translation method based on network requirements and the roles of devices within the network.
This CCNA practice question helps students prepare for Cisco networking certification exams by testing knowledge of network fundamentals, routing, switching, and network security concepts.