lecture 4 supplement

8/13/2019 Lecture 4 Supplement

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Configuring a Router

Configuring Router Name

A router should be given a unique name as one of the first configuration tasks. This task isaccomplished in global configuration mode using the following commands:

Router(config)#hostname TokyoTokyo(config)#

As soon as the Enter key is pressed, the prompt changes from the default host name (Router)to the newly configured host name, which is Tokyo in the example.

Configuring Router Passwords

Passwords restrict access to routers. Passwords should always be configured for virtualterminal lines and the console line. Passwords are also used to control access to privilegedEXEC mode so that only authorized users may make changes to the configuration file.

The following commands are used to set an optional but recommended password on theconsole line:

Router(config)#line console 0Router(config-line)#password Router(config-line)#login

A password must be set on one or more of the virtual terminal (VTY) lines for users to gainremote access to the router using Telnet. Typically Cisco routers support five VTY linesnumbered 0 through 4, although different hardware platforms support different numbers on VTY

connections. The following commands are used to set the password on the VTY lines:

Router(config)#line vty 0 4Router(config-line)#password Router(config-line)#login

If an administrator telnets from one router to a directly connected router and the telnetconnection opens, but the administrator is unable to log on, this is because the virtual terminalpasswords are not defined in the running-configuration.

The enable password and the enable secret are used to restrict access to the privileged EXECmode. The enable password is only used if the enable secret has not been set. It is

recommended that the enable secret always be set and used because it is encrypted while theenable password is not encrypted. These are the commands that are used to set the enablepasswords:

Router(config)#enable password Router(config)#enable secret


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Sometimes it is undesirable for passwords to be shown in clear text in the output from the showrunning-config or show startup-config commands. This command is used to encrypt passwordsin configuration output:

Router(config)#service password-encryption

The service password-encryption command applies a weak encryption to all unencryptedpasswords. The enable secret command uses a strong MD5 algorithm forencryption.

Show Commands

show ip routeDisplays Routing Table of the router show interfacesDisplays all the statistics for all the interfaces on the router. To

view the statistics for a specific interface, enter the show interfaces commandfollowed by the specific interface and port number

show clockShows the time set in the router show historyDisplays a history of commands that have been entered show flash Displays information about flash memory, configuration file and what IOS

files are stored there show versionDisplays information about the configuration file in the router and the IOS

that is running in RAM show ARPDisplays the ARP table of the router show startup-configuration Displays the saved configuration located in NVRAM and

display information about the IOS or configuration files stored in router memory show running-configurationDisplays the configuration currently running in RAM

erase startup-config and reload deletes existing configuration on a router.

Configuring a Serial Interface

A serial interface can be configured from the console or through a virtual terminal line. Toconfigure a serial interface follow these steps:

1. Enter global configuration mode2. Enter interface mode3. Specify the interface address and subnet mask4. Set clock rate if a DCE cable is connected. Skip this step if a DTE cable is connected.5. Turn on the interface by the command Router(config-if)#no shutdown

Each connected serial interface must have an IP address and subnet mask if the interface is

expected to route IP packets. Configure the IP address using the following commands:

Router(config)#interface serial 0/0Router(config-if)#ip address

Router(config)#clock rate 56000Router(config-if)#no shutdown


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Serial interfaces require a clock signal to control the timing of the communications. In mostenvironments, a DCE device such as a CSU will provide the clock. By default, Cisco routers areDTE devices but they can be configured as DCE devices.

By default, interfaces are turned off, or shutdown, meaning they have no IP address. To turn onor enable an interface, the command no shutdown is entered. If an interface needs to be

administratively disabled for maintenance or troubleshooting the command shutdown is used toturn off the interface.

The default state of interfaces on the router is administratively down, line protocol down.

Configuring an Ethernet interface

Each Ethernet interface must have an IP address and subnet mask if the interface is expectedto route IP packets. Also, you should enter the no shut down command to enable the interface.

To configure an Ethernet interface follow these steps:

1. Enter global configuration mode2. Enter interface configuration mode3. Specify the interface address and subnet mask4. Enable the interface

By default, interfaces are turned off, or disabled. To turn on or enable an interface, thecommand no shutdown is entered. If an interface needs to be administratively disabled formaintenance or troubleshooting the command shutdown is used to turn off the interface.

Interface Descriptions

An interface description should be used to identify important information such as a distantrouter, a circuit number, or a specific network segment. A description of an interface can help anetwork user remember specific information about the interface, such as what network theinterface services.

The description is meant solely as a comment about the interface. Although the descriptionappears in the configuration files that exist in router memory, a description does not affect theoperation of the router. Descriptions are created by following a standard format that applies toeach interface. The description may include the purpose and location of the interface, otherdevices or locations connected to the interface, and circuit identifiers. Descriptions allow supportpersonnel to better understand the scope of problems related to an interface and allow for fasterresolution of problems.

Configuring Interface Descriptions

To configure an interface description, enter global configuration mode. From globalconfiguration mode, enter interface configuration mode. Use the command description followedby the information.


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Procedure steps:

1. Enter global configuration mode by entering the command configure terminal.2. Enter specific interface mode (for example interface Ethernet 0) interface ethernet 0.3. Enter the command description followed by the information that is to be displayed. For

example, XYZ Network, Building 18.

4. Exit interface mode back to privileged EXEC mode by using the command ctrl-Z.5. Save the configuration changes to NVRAM by using the command copy running-config

startup-config.

Here is an example of interface descriptions:

Router# configure terminalRouter(config)# interface fa0Router(config-if)# description Engineering LAN

Login Banners

A login banner is a message that is displayed at login and is useful for conveying messages thataffect all network users, such as notices of impending system shutdowns. It can be used todisplay dated information regarding system change.

Login banners can be seen by anyone. Therefore, careful attention should be used in thewording of a banner message. Welcome is an invitation for anyone to enter a router and isprobably not an appropriate message.

A login banner should be a warning not to attempt login unless authorized. A message such asThis is a secure system, authorized access only! instructs unwanted visitors that any furtherintrusion is unwanted and illegal.

Configuring message of the Day (MOTD)

A message-of-the-day (MOTD) banner can be displayed on all connected terminals.

Follow these steps to create and display a message-of-the-day:

1. Enter global configuration mode by using the command configure terminal.2. Enter the command banner motd # The message of the day goes here #.3. Save changes by issuing the command copy running-config startup-config.

Host Name Resolution

Host name resolution is the process that a computer system uses to associate a host name withan IP address.

In order to use host names to communicate with other IP devices, network devices such asrouters must be able to associate the host names with IP addresses. A list of host names andtheir associated IP addresses is called a host table.


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A host table might include all devices in a network organization. Each unique IP address canhave a host name associated with it. The Cisco IOS software maintains a cache of host name-to-address mappings for use by EXEC commands. This cache speeds up the process ofconverting names to addresses.

Host names, unlike DNS names, are significant only on the router on which they are configured.

The host table will allow the network administrator to type either the host name such asAuckland or the IP address to Telnet to a remote host

Example:

Router(config)# ip host Auckland 172.16.32.1

Configuring Host Tables

To assign host names to addresses, first enter global configuration mode. Issue the commandip host followed by the name of the destination and all IP addresses where the device can bereached. This maps the host name to each of its interface IP addresses. To reach the host, use

a telnet or ping command with the name of the router or an IP address that is associated withthe router name.

The procedure to configure the host table:

1. Enter global configuration mode in the router.2. Enter the command ip host followed by the name of the router and all IP addresses

associated with the interfaces on each router.3. Continue entering until all routers in the network are entered.4. Save the configuration to NVRAM.

If telnet session can be established when using the IP address of a router but not the name ofthe router, the problem is on incorrect host table entry.

Configuration Backup and Documentation

Configuration files should be stored as backup files in the event of a problem. Configuration filescan be stored on a network server, on a TFTP server, or on a disk stored in a safe place.

Copying, editing and pasting configuration

A current copy of the configuration can be stored on a TFTP server. The copy running-configtftp command, can be used to store the current configuration on a network TFTP server. To do

so, complete the following tasks:

Step 1 Enter the copy running-config tftp command in privileged mode.

Step 2 Enter the IP address of the host where the configuration file will bestored.

Step 3 Enter the name to assign to the configuration file.


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Step 4 Confirm the choices by answering yes each time.

Configure Dynamic Routing Protocol and Table

Router(config)#router ripRouter(config-router)#network 192.168.14.0Router(config-router)#network 192.168.15.0Router(config-router)#exit

Configure Static Route and Default Static Route

Router(config)#ip route 192.168.14.0 255.255.255.0 Serial 0/0orRouter(config)#ip route 192.168.14.0 255.255.255.0 192.168.15.1

Router(config)#ip route 0.0.0.0 0.0.0.0 Serial 0/0orRouter(config)#ip route 0.0.0.0 0.0.0.0 192.168.15.1

Additional commands:

no ip domain-lookup Disables DNS lookup entered inglobal configuration mode

logging synchronous Command use to avoidunsolicited messages from

interfering with the commandsbeing entered. Done in lineconfiguration mode

no ip classless Disable classless IP routingentered in global configurationmode

lecture 4 supplement

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