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Router Basics

This article covers the fundamental aspects of routers, including their purpose, functions, hardware components, interface types, boot-up process, user interface, and command-line interface. It provides insights into how a router operates as a computer, directing packets to their destinations efficiently. Readers will learn about essential components like RAM, ROM, NVRAM, Flash memory, and interfaces. Understanding the router boot-up process, interface types, and user modes is vital for effective network setup and management.

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Router Basics

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  1. Router Basics รศ. ดร. อนันต์ผลเพิ่ม Asso. Prof. Anan Phonphoem, Ph.D. anan.p@ku.ac.th Intelligent Wireless Network Group (IWING Lab) http://iwing.cpe.ku.ac.th Computer Engineering Department Kasetsart University, Bangkok, Thailand

  2. Router as a Computer • Basic purpose of a router • Computers that specialize in sending packets over the data network • Routers are the network center • generally have 2 connections: • -WAN connection (Connection to ISP) • -LAN connection

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

  4. Router functions • examine a packet’s destination IP address • find the best path

  5. Router (Hardware components) • Router components

  6. Router components • CPU (Executes operating system instructions) • Random access memory (RAM) • Read-only memory (ROM) • Non-volatile RAM (NVRAM) • Flash memory • Interfaces (multiple physical interfaces)

  7. RAM NVRAM Flash ROM Console Interfaces Auxiliary Internal Components

  8. RAM • Running copy of configuration file • RAM content is lost on power down • Stores... • Routing tables • ARP cache • Fast switching cache • Packet buffering • Packet hold queues

  9. ROM • Contains POST • diagnostic software: Power On Self Test • A bootstrap program (loads the Cisco IOS) • And operating system software • Backup, trimmed down version of the IOS • Upgrades require installing new chip set

  10. NVRAM • Non-volatile RAM • Stores backup/startup configuration files • IP addresses, Routing protocol, Hostname of router • Content is not lost when router is powered down or restarted.

  11. Flash • EEPROM • Electronically Erasable Programmable Read-Only Memory • Holds the Cisco IOS • Allows updating of software without replacing the Flash chip • Store Multiple versions of IOS • Retained on power down

  12. Router Interface • 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 • Attached to the motherboard or as separate modules • Examples of interface types: • Ethernet / fast Ethernet interfaces • Serial interfaces / DSL / ISDN • Management interfaces

  13. Major Router Interfaces • LAN Interfaces: • connect router to LAN network • has a layer 2 MAC address • can be assigned a Layer 3 IP address • usually consist of an RJ-45 jack

  14. Major Router Interfaces • WAN Interfaces: • connect routers to external networks that interconnect LANs • depending on the WAN technology, a layer 2 address may be used. • uses a layer 3 IP address

  15. Router boot-up process

  16. Verify router boot-up process • “show version” • 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

  17. Using the Router • Understand the Basics of Router's Command Line Interface (CLI). • Demonstrate How to Log into the Router. • Demonstrate How to Enter Router Modes. • Demonstrate Ability to Discern Different Router Modes and Commands

  18. Router User Interface

  19. User Interface • To config: router console • user mode—Typical tasks include those that check the router status. In this mode, router configuration changes are not allowed. • privileged mode—Typical tasks include those that change the router configuration.

  20. Means you’re in user mode User EXEC Modes • User mode (Limited mode) • Checking the routers status, looking at routing tables, etc. • You cannot configure the router • Prompt = “>” Password: Router>

  21. Means you’re in privileged mode Privileged EXEC Modes • Privileged mode • Does everything User mode does • Full power to configure the router • In user mode, you enter the command “enable” and then the privileged password Router> enable Password: Router#

  22. Command Lists • To get a list of commands available in either user mode or privileged mode, enter a ? at the prompt. Router> ? Router# ?

  23. The Router returned all the available commands for “show” Getting Help on a Command • The ? can be used with a partial command • To use this help feature, enter the partial command, then tap the space bar, then type ? • For example... ip flash: interfaces ipx version parser Router# show ?

  24. More-- you can continue viewing onto the next available screen by pressing the space bar Typing a question mark (?) displays a handy list of commonly used commands.

  25. To access privileged mode, type enable (or the abbreviation ena) . You will be prompted for a password.

  26. Use help to check the syntax for setting the clock. The help output shows that the set keyword is required Press Ctrl-P (or the up arrow key) to repeat the previous command entry automatically. The caret symbol (^) and help response indicate an error. To list the correct syntax

  27. Error Indicator • a carat (^) symbol will indicate where the error occurred. • For example... Router# show runing-config ^ % Invalid input detected at the ‘^’ marker

  28. The Show Command

  29. Router#show interfaces Router#show version Router#show flash Router#show mem Router#show stacks Router#show buffers Router#show processes CPU Router#show protocols Router#show running-config Router#write term Router#show startup-config Router#show config Router Status Commands RAM NVRAM Flash Internetwork Operating System Backup Configuration File Operating Systems Interfaces Programs Active Configuration File Tables and Buffers

  30. Show Commands • show version • show running-config • show startup-config • show interfaces • show memory • show flash • show processes • show protocols • show stacks • show buffers

  31. show version

  32. Main Topology

  33. Routers and the Network Layer • use destination IP address to forward packets • The path a packet takes is determined after a router consults information in the routing table. • After router determines the best path • Packet is encapsulated into a frame • Frame is then placed on network medium in form of Bits

  34. Router as a Computer • Routers Operate at Layers 1, 2 & 3 • Router receives a stream of encoded bits • Bits are decoded and passed to layer 2 • Router de-encapsulates the frame • Remaining packet passed up to layer 3 • -Routing decision made at this layer by examining destination IP address • Packet is then re-encapsulated & sent out outbound interface

  35. Configure Devices and Apply Addresses • Implementing Basic Addressing Schemes • When designing a new network or mapping an existing network you must provide the following information in the form of a document: • -Topology drawing that Illustrates physical connectivity • Address table that provides the following information: • Device name • Interfaces used • IP addresses • Default gateway

  36. Configure Devices and Apply Addresses • Basic Router Configuration • A basic router configuration should contain the following: • -Router name - Host name should be unique • -Banner - At a minimum, banner should warn against unauthorized use • -Passwords - Use strong passwords • -Interface configurations - Specify interface type, IP address and subnet mask. Describe purpose of interface. Issue no shutdown command. If DCE serial interface issue clock rate command. • After entering in the basic configuration the following tasks should be completed • -Verify basic configuration and router operations. • -Save the changes on a router

  37. Configure Devices and Apply Addresses

  38. Configure Devices and Apply Addresses • Verify Basic Router Configuration • -Issue the show running-config command • -Save the basic router configuration by Issuing the copy running-config startup-config command • -Additional commands that will enable you to further verify router configuration are: • Show running-config - Displays configuration currently in RAM • Show startup-config - Displays configuration file NVRAM • Show IP route - Displays routing table • Show interfaces - Displays all interface configurations • Show IP int brief - Displays abbreviated interface configuration information

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