This document provides an overview of router hardware, software, memory, interfaces, and configuration. It discusses what a router consists of, including CPU, memory, interfaces, and IOS software. RAM is used to store the running IOS, configuration, routing table, ARP cache, and packet buffer. ROM stores boot files. Flash stores the IOS image. NVRAM stores the startup configuration. The document outlines the boot-up process and describes router interfaces, access methods, and Cisco IOS modes including privileged EXEC mode for configuration. It provides examples of basic router configuration commands.

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Network Fundamentals
Abdelkhalik Elsaid Mosa
abdu.elsaid@yahoo.com
http://abdelkhalik.staff.scuegypt.edu.eg/

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What is a Router?
• Front View
• Rear View

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What is a Router?
Router is a computer which consists of
H/W S/W
CPU InterfacesMemory IOS Config File
Flash NVRAM RAM ROM LAN WANManagement

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Router’s Memory
• RAM «volatile»: used to store
1. Running version of IOS.
2. Running config. File.
3. Routing table.
4. ARP Cache «is used on routers that have LAN interfaces».
5. Packet Buffer.
• ROM «permanent»: used to store
1. POST, Basic diagnostic software.
2. Bootstrap.
3. Scaled down Version of IOS «Rxboot».
4. ROMMon.
• Flash «Non volatile»: used to store IOS.
• NVRAM: used to store Start Up Configuration.

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Router Boot-up Process

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Router’s Interfaces
• Router Interfaces: capable of sending and receiving traffic.
1. LAN
2. WAN
• Management Ports: used for administrative access.
1. Console
2. AUX

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Cisco IOS - Access Methods
• The most usual methods are:
1. Console: Doesn’t require active networking services.
2. AUX port: Doesn’t require active networking services.
3. Telnet or SSH: Requires active networking services.

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Console Port
• Examples of console use are:
The initial configuration of the network device
Disaster recovery procedures and troubleshooting where
remote access is not possible.
Password recovery procedures.

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Using HyperTerminal

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Auxilary Port

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Cisco IOS Modes
• Cisco IOS is a Modal OS.
• In order from top to bottom, the modes are:
1. Setup mode.
2. User executive mode “view only mode”
3. Privileged executive mode “enable mode”
4. Global configuration mode
5. Other specific configuration modes

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Setup mode
• Permit admin to install a minimal configuration for a router.
• The router will enter setup mode when:
 Contents of NVRAM erased “erase startup” command.
 When the router is “out of the box”.
• You can make the router enter setup mode by entering:
 Router# setup

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User executive mode
• Allows only a limited number of basic monitoring commands.
• Often referred to as a “view only” mode.
• Does not allow any commands that might change the
configuration of the router.
• Identified by the > prompt.

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Privileged executive mode
• Provides access to all router commands.
• This mode can be configured to require a password.
• Global configuration mode and all other more specific
configuration modes can only be reached from the privileged
EXEC mode.
• The privileged EXEC mode can be identified by the # prompt.

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Global configuration & Specific Configuration
• Configuration changes are made that affect the operation of
the device as a whole.

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Basic IOS command structure

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Using CLI help
• The IOS has several forms of help available:
1. Context-sensitive help
2. Command Syntax Check
3. Hot Keys and Shortcuts

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Context-sensitive help

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Command Syntax Check

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Hot Keys and Shortcuts
• Tab: Completes the remainder of the command or keyword.
• Ctrl-R: Redisplays a line
• Ctrl-Z: Exits configuration mode and returns to the EXEC.
• Down Arrow: Scroll forward through former commands.
• Up Arrow: Scroll backward through former commands
• Ctrl-Shift-6: Interrupt an IOS process such as ping or tracert.
• Ctrl-C: Aborts the current command and exits the
configuration mode.
• Abbreviated commands: Commands can be abbreviated to
the minimum number of characters that identifies a unique
selection. Ex: sh int = show interfaces

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IOS examination commands
• Show version
• Show flash
• Show interfaces
• Show startup-config
• Show running-config

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Basic Router Configuration
• Naming the router: Host name should be unique.
• Banner: Banner should warn against unauthorized use.
• Passwords: Use strong passwords
• Privileged mode password
• Console Password
• Telnet Password

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Basic Router Configuration
• Interface configurations: interface type, IP address and
subnet mask. Describe purpose of interface. Issue no
shutdown command. If DCE serial issue clock rate command.

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Configuring a serial interface
S0/0
S0/1
192.168.1.1/30
192.168.1.2/30
RouterA(config)# interface serial 0/0
RouterA(config-if)# ip address 192.168.1.1 255.255.255.0
RouterA(config-if)# no shutdown
RouterA(config-if)# clock rate 56000 (required for serial DCE only)
RouterA(config-if)# exit
RouterB(config)# int serial 0/1
RouterB(config-if)# ip address 192.168.1.2 255.255.255.252
RouterB(config-if)# no shutdown
RouterB(config-if)# exit
RouterB(config)# exit
Router#
To know which interface is the DCE :
RouterA# show controller s0/0

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Interpreting the Interface Status
• Other Interface Status
• Serial0/1 is administratively down , line protocol is down
 interface is shut down
• Serial0/1 is down , line protocol is down
 interface or cable H/W failure ( no keep-alives )
• Serial0/1 is up , line protocol is down
 different encapsulation type ( PPP , HDLC , FR ) or no clock rate on DCE.
Layer 1 status Layer 2 status
Interface
is working
properly

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Just Refresh – Enable Mode commands
• copy running-config startup-config
• copy startup-config running-config
• erase startup-config
• ping ip_address
• traceroute ip_address
• show interfaces
• show version
• show arp
• show startup-config
• show running-config
• show ip interface brief
• configure terminal
• show controllers serial_interface

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