Which type of memory stores the configuration of a router or switch by default?

By default, Cisco routers and switches store their startup configuration file (startup-config) in Non-Volatile Random Access Memory (NVRAM). NVRAM is a type of memory that retains its contents even when the device is powered off. When a device boots, it loads the startup-config from NVRAM into RAM to become the active running-config. RAM is volatile and stores the active configuration, while flash memory primarily stores the Cisco IOS software image. ROM contains the bootstrap program used to start the device.

A. RAM: RAM (Random Access Memory) is volatile and stores the running configuration, which is lost when the device loses power.
B. ROM: ROM (Read-Only Memory) stores the bootstrap program and Power-On Self-Test (POST) diagnostics, not the user-saved configuration file.
D. flash: Flash memory is non-volatile, but its primary purpose is to store the Cisco Internetwork Operating System (IOS) image, not the default startup configuration.

1. Cisco Systems, Inc., "Router and Switch Memory Components," Cisco Technical Support & Documents. This document explicitly states: "Non-Volatile RAM (NVRAM) - Stores the startup configuration file." and "RAM/DRAM - Stores the running configuration file."

Reference: Document ID: 15113, Section: "Memory Components".

2. Cisco Systems, Inc., "Cisco IOS Configuration Fundamentals Configuration Guide, Release 12.2," Managing Configuration Files Overview. This guide details the configuration file management process, specifying that the startup configuration is stored in NVRAM.

Reference: Chapter: "Managing Configuration Files," Section: "Configuration Files".

3. Wendell Odom, "CCNA 200-301 Official Cert Guide, Volume 1," Cisco Press. While a certification guide, Cisco Press is the official publishing arm of Cisco.

Reference: Chapter 2, "Fundamentals of Ethernet LANs," Section: "Accessing the Cisco IOS CLI," Sub-section: "Volatile and Nonvolatile Storage on a Cisco Switch," clearly defines NVRAM as the storage for the startup-config file.