1. Router Basics รศ. ดร. อนันต์ ผลเพิ่ม Asso. Prof. Anan Phonphoem, Ph.D.
Intelligent Wireless Network Group (IWING Lab)
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. Internal Components
RAM
NVRAM
Flash
ROM
Console
Interfaces
Auxiliary

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 A bootstrap program (loads the Cisco IOS)
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 Holds the Cisco IOS
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>
Means you’re in user mode

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#
Means you’re in privileged mode

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

24. 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 ?
The Router returned all the available commands for “show”

25. 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.

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

27. Use help to check the syntax for setting the clock
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

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

29. The Show Command

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

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

32. show version

33. Main Topology

34. 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

35. 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

36. 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

37. 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

38. Configure Devices and Apply Addresses

39. 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