Introduction to Routing and Packet Forwarding

Routing Protocols and
Concepts – Chapter 1

Version 4.0

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Objectives
§ Identify a router as a computer with an OS and hardware designed for the routing process.
§ Demonstrate the ability to configure devices and apply addresses. § Describe the structure of a routing table.
§ Describe how a router determines a path and switches packets.

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Router as a Computer
§ Describe the basic purpose of a router
– 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 are the network center
– Routers generally have 2 connections:
• WAN connection (Connection to ISP)
• LAN connection

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Router as a Computer
§ Data is sent in form of packets between 2 end devices
§ Routers are used to direct packet to its destination

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Router as a Computer
§ Routers examine a packet’s destination IP address and determine the best path by enlisting the aid of a routing table © 2007 Cisco Systems, Inc. All rights reserved.

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Router as a Computer
§ Router components and their functions:
– CPU - Executes operating system instructions
– Random access memory (RAM) - Contains the running copy of configuration file. Stores routing table. RAM contents lost when power is off.
– Read-only memory (ROM) - Holds diagnostic software used when router is powered up. Stores the router’s bootstrap program. – Non-volatile RAM (NVRAM) - Stores startup configuration.
This may include IP addresses (Routing protocol, Hostname of router). – Flash memory - Contains the operating system (Cisco IOS).
– Interfaces - There exist multiple physical interfaces that are used to connect network. Examples of interface types:
• Ethernet / fast Ethernet interfaces
• Serial interfaces
• Management interfaces
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Router as a Computer
§ Router components

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Router as a Computer
§ Major phases to the router boot-up process
– Test router hardware
• Power-On Self Test (POST)
• Execute bootstrap loader
– Locate & load Cisco IOS software
• Locate IOS
• Load IOS
– Locate & load startup configuration file or enter setup mode
• Bootstrap program looks for configuration file

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Router as a Computer
§ Verify the router boot-up process:
– The show version command is used to view information about the router during the bootup process. Information includes:
• Platform model number
• Image name & IOS version
• Bootstrap version stored in ROM
• Image file name & where it was loaded from
• Number & type of interfaces
• Amount of NVRAM
• Amount of flash
• Configuration register

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Router as a Computer

© 2007 Cisco Systems, Inc. All rights reserved.

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Router as a Computer
§ Router Interface is a physical connector that enables a router to send or receive packets
§ Each interface connects to a separate network
§ Consist of socket or jack found on the outside of a router § Types of router interfaces:
– Ethernet
– Fastethernet
– Serial
– DSL
– ISDN
– Cable

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Router as a Computer
§ Two major groups of Router Interfaces
– LAN Interfaces
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Are