Networking Chapter 8: Switching and Routing

IOS in a Router or Switch

• The IOS (Internetwork Operating System) is the software that runs on a router or switch, providing the instructions for its operation.

Similarity to a Computer

• The IOS of a router is similar to that of a computer, as both require software to function and perform specific tasks.

Main Function of a Router

• The main function of a router is to connect multiple networks together and route traffic between them.

Importance of Understanding IOS

• A solid understanding of the IOS is essential for a network administrator to configure, manage, and troubleshoot a router.

Functions Performed by Routers

• Routers perform several specific functions, including:
• Routing traffic between networks
• Providing network address translation (NAT)
• Filtering traffic using access control lists (ACLs)
• Providing quality of service (QoS)

Configuration Files

• The configuration files used by routers contain instructions and parameters, such as:
• IP addresses
• Subnet masks
• Routing tables
• ACLs

Non-Volatile RAM (NVRAM)

• NVRAM is a type of memory that retains its contents when the router is powered down or restarted.
• NVRAM stores the router's configuration, including the startup-config file.

IOS Image Storage

• The IOS image is stored in Flash memory.

Power-On Self-Test (POST) Diagnostics

• The Boot ROM (Read-Only Memory) contains instructions for power-on self-test (POST) diagnostics, which run when the router is powered on.

Routing Tables and ARP Cache

• The RAM (Random Access Memory) stores the routing tables and ARP (Address Resolution Protocol) cache.

Interface Types

• The WAN (Wide Area Network) interface connects the router to a network for frame entry and exit.

Bootup Sequence

• After the power-on self-test (POST), the router loads the IOS image from Flash memory and starts the bootup sequence.

Configuration Register

• The configuration register contains settings that control the bootup sequence, such as the location of the IOS image.

Flash Memory

• Flash memory stores the IOS image and is a non-volatile type of memory that retains its contents when the router is powered down or restarted.

RAM Functions

• RAM holds the ARP cache and performs packet buffering, as well as stores the routing tables.