Introduction to Routing and Packet Forwarding

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Introduction to Routing and Packet Forwarding Introduction to Routing and Packet Forwarding Introduction to Routing and Packet Forwarding Routing Protocols and Concepts – Chapter 1 ITE PC v4.0 1 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Objectives Identify a router as a computer with an OS and de as co OS hardware designed for the routing process. Demonstrate the ability to configure devices and Demonstrate the ability to configure devices and apply addresses. Describe the structure of routing table Describe the structure of a routing table. Describe how a router determines a path and switches packets switches packets ITE PC v4.0 2 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Router as a Computer Describe the basic purpose of a route bas pu er -Computers that specialize in sending packets over the data network. They are responsible for interconnecting networks by selecting the best path for a packet to travel and forwarding packets to their destination Routers have many of the same hardware and software components that are found in other computers including: –CPU –RAM –ROM –Operating System ITE PC v4.0 3 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Router as a Computer Router components and their functions” CPU - Executes operating system instructions such as system initialization, routing functions, and switching functions. Random access memory (RAM) -RAM stores the instructions and data needed access memory (RAM) stores the instructions and data needed to be executed by the CPU. RAM is used to store these components: –Operating System: The Cisco IOS (Internetwork Operating System) is copied into RAM during bootup. –Running Configuration File: This is the configuration file that stores the configuration commands that the router IOS is currently using. –IP Routing Table: This file stores information about directly connected and remote networks. It is used to determine the best path to forward the packet. –ARP Cache: This cache contains the IPv4 address to MAC address mappings, similar to the ARP cache on a PC. The ARP cache is used on routers that have LAN interfaces such as Ethernet interfaces. LAN –Packet Buffer: Packets are temporarily stored in a buffer when received on an interface or before they exit an interface. RAM is volatile memory and loses its content when the router is powered down or restarted. ITE PC v4.0 4 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Router as a Computer Router components and their functions” co Read-only memory (ROM) - Holds diagnostic software used when router is powered up. Stores the router’s bootstrap program. –ROM is a form of permanent storage. Cisco devices use ROM to store: –The bootstrap instructions –Basic diagnostic software –Scaled-down version of IOS version of IOS ROM uses firmware, which is software that is embedded inside the integrated circuit. – Firmware includes the software that does not normally need to be modified or upgraded, such as the bootup instructions. – ROM does not lose its contents when the router loses power or is restarted. ITE PC v4.0 5 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Router as a Computer Router components and their functions” Non-volatile RAM (NVRAM) - Stores startup configuration. This may include IP addresses (Routing protocol Hostname of router) addresses (Routing protocol, Hostname of router) NVRAM (Nonvolatile RAM) does not lose its information when power is turned off. This is in contrast to the most common forms of RAM, such as DRAM, that requires continual power to maintain its information. NVRAM is used by the Cisco IOS as permanent storage for the startup configuration file. is used by the Cisco IOS as permanent storage for the startup configuration file ...