Your customer is concerned about security. He wants to make certain no one in the outside world can see the IP addresses inside his network. What feature of a router would accomplish this?

Network Address Translation (NAT) is a method used by routers to map multiple private, non-routable IP addresses (e.g., from the 192.168.0.0/16 range) to a single, public, routable IP address. When a device on the internal network sends a packet to the internet, the NAT router replaces the private source IP address with its own public IP address. To any external observer, all traffic appears to originate from the router itself, effectively hiding the internal network's structure and specific IP addresses. This is a fundamental function of NAT and directly addresses the customer's requirement.

A. Port forwarding: This feature selectively exposes specific internal services to the external network; it does not hide the internal network.
C. MAC filtering: This is a Layer 2 security control that restricts network access based on a device's hardware address, not its IP address.
D. Firewall: A firewall's primary function is to filter traffic based on a set of rules, not to translate or hide IP addresses, which is the specific role of NAT. ---

1. National Institute of Standards and Technology (NIST) Special Publication 800-41 Rev. 1

Guidelines on Firewalls and Firewall Policy.

Section 4.4

Network Address Translation (NAT): "Network Address Translation (NAT) is the translation of an IP address used within one network to a different IP address known within another network... NAT can also provide a type of security by hiding internal IP addresses from external networks."

2. Internet Engineering Task Force (IETF) RFC 2663

IP Network Address Translator (NAT) Terminology and Considerations.

Section 1

Introduction: This document describes how NAT is used to "alleviate the IP address depletion problem" and notes its side effect of providing a form of "firewall" by hiding the internal network topology.

3. Peterson

L.

& Davie

B. (2011). Computer Networks: A Systems Approach (5th ed.). Morgan Kaufmann.

Section 4.1.4

Network Address Translation (NAT): "The key idea is that NAT is implemented on a border router that has one interface on the inside (local) network and one on the outside (global) network... To the outside world

the entire local network looks like a single host with the IP address of the outside interface of the NAT box."

4. Kurose

J. F.

& Ross

K. W. (2017). Computer Networking: A Top-Down Approach (7th ed.). Pearson.

Section 4.4.2

The Network Address Translation (NAT) Router: "From the outside world

all datagrams leaving the home network for the larger Internet have the same single source NAT IP address... The hosts inside the home network are not directly addressable or visible by the outside world."