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Configuring and Testing Your Network

Network Fundamentals – Chapter 11

Dr. C. BouSaba

Topics

� The Internetwork Operating System (IOS).

� Devices that have the IOS embedded.

� IOS commands available to a device.

� IOS modes of operation.

� Basic IOS commands.

� Basic show commands.

� Configuration files

Internetwork Operating System

� Most Cisco devices use the Cisco IOS.

� Details vary with the device and feature set.

� Normal access through a command line.

� Stored in flash memory and can be upgraded.

� Usually copied into RAM when the device is powered on, and run from RAM.

Role of Internetwork Operating System (IOS)

Access to the interface

� Console port via serial connection

Initial configuration

Disaster recovery

When network access has failed

Password recovery

As well as general management

� Console access does not require a password. Configure a password. Lock the door.

Telnet, SSH, Aux

� Later management can be via Telnet

� There must be an IP address on the port

� A password must be configured

� Secure shell gives better security

� AUX port can be used locally or via modem but by default does not show error messages

Configuration files

� Hold the commands that have been configured on the router to customise it.

� Running configuration in RAM holds commands that are in current use

� Startup configuration in NVRAM holds saved commands. These are kept when the power is off and usually copied back into RAM when the router is re- started.

Router storage areas

� ROM

� Permanent

� Holds POST, boot instructions, basic IOS

� Flash

� Keeps contents

� Holds IOS image

� NVRAM

� Keeps contents

� Holds startup configuration file

� RAM

� Volatile

� Holds runnning config, tables, queues etc

Router IOS modes

User EXEC mode

Privileged EXEC mode

enable disable + password

Global Configuration mode

Configure terminal Exit or Ctrl+z

Specific Configuration modes

Exit EndVarious commands

Router prompts

User EXEC mode

Privileged EXEC mode

Global Configuration mode

Specific Configuration modes

Router>

Router#

Router(config)#

Router(config-if)# and others

IOS Mode Hierarchical Structure � Cisco IOS is modal and each mode has implications

IOS Primary Modes

EXEC modes

� You log in to User EXEC mode Router>

� You can give basic monitoring commands but cannot change the configuration

� Enter enable to go to Privileged EXEC mode Router#

� Password may be used for security

� You can give more commands and can go to configuration modes

Configuration modes

� Start in privileged EXEC mode and enter the configure terminal (config t) command Router# config t Router(config)#

� The prompt changes

� This is global configuration mode

� Additional commands take you to interface configuration, router configuration etc.

Leaving configuration modes

� From interface configuration mode there are several ways of getting to privileged EXEC

� Router(config-if)# exit Router(config)# exit Router#

� Router(config-if)# end Router#

� Router(config-if)# Ctrl+z Router#

IOS Configuration Modes

Basic IOS Command Structure

Command Structure

Followed by <Enter>

? To get help

� ? Gives a list of commands available from the current prompt.

� Command followed by space then ? Gives a list of keywords or arguments that can be used.

� Start of command followed by ? with no space shows how the word can be continued.

? To get help

Shortened commands

� Router#show running-config

� Router#show run

� Router#sh ru

� It needs enough letters of each word to be unambiguous. (Tab key shows whole word)

� Router#s ru

� % Ambiguous command: ‘s’

Other error messages

� Switch#clock set

� % Incomplete command

� Switch#clock set 19:50:00 25 6

� % Invalid input detected at ‘^’ marker

� Router#show runming-config

� % Invalid input detected at ‘^’ marker

Keyboard shortcuts

� Tab completes a partial command

� Backspace erases to left of cursor

� Ctrl+D erases at cursor (Delete does not)

� Ctrl+Z returns from any config mode to privileged exec mode

� Ctrl+C leave Setup mode

At the ---More--- prompt

� Enter shows the next line

� Spacebar shows the next screenful

� Needed with commands such as show running-config that produce more than one screen of text.

Show Command and its Variations

Show commands

� Show ? To get a list

� Many different show commands to give information about every aspect of the router and its operation

� We use some of the most common.

General show commands

� Show running-config shows the configuration file from RAM

� Show startup-config shows the saved configuration file from NVRAM

� Show version gives information about the IOS and the router itself. It shows the configuration register, which controls how the router starts up.

Show interfaces

� Gives statistics for all interfaces

� In particular, says if the interface is up and if the protocol is up – important in troubleshooting.

� Show interfaces serial 0/0 to show one selected interface

� You can shorten to show int s 0/0

� Show ip interfaces gives IP statistics

Save configuration

� Router#copy running-config startup-config

� Router#copy run start (shortened)

� Router#wr (Old fashioned, short for write, but it works and is safe.)

� Beware! A typing error in the copy command can delete the operating system. If you get an odd message about Flash – hands off – call for help.

Hostname

� Router>enable

� Router#config t

� Router(config)#hostname Paris

� Paris(config)#

� Configure a suitable hostname so that you know which router you are managing and so that you can identify it in network documentation.

Console password

� Paris(config)#line con 0

� Paris(config-line)#password cisco

� Paris(config-line)#login

� Paris(config-line)#exit

� Restricts access via the console

� Use cisco as the password in labs.

� Use a proper strong password on production networks

Vty password for Telnet

� Paris(config)#line vty 0 4

� Paris(config-line)#password cisco

� Paris(config-line)#login

� Paris(config-line)#exit

� Allows and restricts access via 5 vty lines

� Use cisco as the password in labs.

� Use a proper strong, different password on production networks

Enable and enable secret

� Paris(config)#enable secret class

� The password class is needed when you type enable to enter privileged exec mode

� This password is encrypted

� Paris(config)#enable password cisco

� Not encrypted, used on older routers

� If you configure both, then only the enable secret is used.

Message of the day

� Paris(config)#banner motd # No unauthorized access #

� # is a delimiter to show where the message starts and ends.

� Any character can be used as long as it does not appear in the message.

� The message should make it clear that unauthorized access is forbidden.

Reload

� Shuts down the router and then starts it again.

� If the configuration has changed then you are prompted to save it.

� The running configuration in RAM is lost.

� The startup configuration from NVRAM is (usually) loaded into RAM on startup.

Back up to TFTP server

� Start TFTP server software on host

� Paris#copy running-config tftp

� Remote host []? 172.16.1.1

� Name of configuration file to write [Paris-config]? Paris27Oct09

� Write file Paris12Oct07 to 172.16.1.1? [confirm] y

� Writing Paris12Oct07 ! ! ! ! ! ! [OK]

Back up as text file

� Start text capture

� Name file

� show run

� Stop text capture

� Open saved file and “tidy up”.

� Remove unwanted symbols at –More---

� No shutdown command on interfaces

� Passwords in plain text (ouch!)

TeraTerm text file

� TeraTerm is an open source Telnet client.

� It can also act as a SSH client

� It can capture text and save it as a file.

Erase startup configuration

� Paris#erase NVRAM:startup-config

� Paris#erase startup-config

� Paris#erase start

� If you reload, then the router starts up with the default configuration. No passwords, no IP addresses etc.

� Caution if you get this command wrong then you could erase something else, e.g. IOS

Restore file from TFTP server

� Router#copy tftp running-config

� You will be prompted for IP address and file name.

� Configuration is copied into RAM and takes effect at once.

� Save to NVRAM.

Restore text file

� Go to global configuration mode

� Hyperterminal Transfer menu

� Send text file…

� Copy text from text file

� “Paste to host” into Hyperterminal session

Configure a router interface

� Paris(config)#interface FastEthernet 0/0

� Paris(config-if)#ip address 172.16.1.1 255.255.0.0

� Paris(config-if)#no shutdown

� Paris(config-if)#exit

� Interface names vary, depending on whether the router is modular and on the bandwidth.

� E.g. interface Ethernet 0 on an older router

Configure a router interface

� Paris(config)#interface serial 0/0

� Paris(config-if)#ip address 192.168.4.1 255.255.255.0

� (Paris(config-if)#clock rate 64000)

� Paris(config-if)#no shutdown

� Paris(config-if)#exit DCE only

Description

� Paris(config)#interface fa0/0

� Paris(config-if)#description Connects to Paris central switch

� Can include circuit and contact information

� Not needed for the operation of the router

� Valuable for documentation as it is included in the configuration listing

Switch interfaces

� Switch physical interfaces do not have IP addresses

� They are active by default and do not need the no shutdown command.

� It can be useful to give them a description.

Switch IP address

� The switch IP address goes on a virtual interface, not a real one, normally VLAN1.

� SwA(config)#interface VLAN1

� SwA(config-if)#ip address 172.16.255.1 255.255.0.0

� SwA(config-if)#no shutdown

� SwA(config-if)#exit

Switch default gateway

� SwA(config)#ip default gateway 172.16.255.254

� Just like a workstation, a switch needs a default gateway if it exchanges messages with devices on a different network.

� The default gateway is the address of the local router.

Interface – show commands

� show interfaces states whether up or down, gives some protocol information and statistics about interface use.

� show ip interface gives IP addresses and much more.

� show ip interface brief gives summary of IP addresses and whether up/down. Very useful command.

Up or down

� Interface status: Layer 1

Down

Administratively down (no shutdown to bring up)

� Protocol: Layer 2

Down (no keepalive signal received)

Ping – step by step

� Ping 127.0.0.1 (loopback, is TCP/IP OK?)

� Ping own IP address (are NIC hardware and software all right? Is IP address bound?)

� Ping local hosts (checks own configuration and that of others)

� Ping gateway

� Ping other intermediate routers

� Ping hosts on remote networks

Network baseline

� Measure and record performance

At different times

Under different conditions

Repeatedly over a period of time

� Build up a record of network performance

� Useful in troubleshooting and optimising the network

� Helps predict future problems

� Helps planning for change

Find out about nodes

� Ping – used from workstation, router or switch – shows if destination can be reached

� Traceroute – shows hops along the path

� Arp -a on workstation – shows list of MAC and IP addresses

� show mac-address-table on switch – shows list of MAC addresses and switch ports

Accessing Various IOS Configuration Modes

Example

� Use a text file to backup and restore config settings