Monday, April 23, 2018

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Routers and Routing Basics - Configuring a Router

IOS EXEC and Config Modes

Initial Router Configuration

• To alter a router’s configuration, enter global config mode.

– Router# configure terminal

– Router(config)# exit (or hit CTRL+Z)

– Router#

• First task should be to uniquely name the router...

– Router(config)# hostname Sydney

– Sydney(config)#

• ... then restrict router accesswith password security.

– Restrict router session access via all lines, eg. virtual terminal

– Enhance password security with service password-encryption

• Router(config)# service password-encryption

• Router(config)# line vty 0 4

• Router(config-line)# password guessmeifyoucan

• Router(config-line)# login

• Router(config-line)# logging synchronous

– Restrict ability to alter router configuration by passwording access to Privileged EXEC mode, preferably using enable secret to make an encrypted password.

Halt! Who goes there?

Time for ‘Show and Tell’!

• show commands display various aspects of the current router configuration.

– show running-config: Displays the contents of the currently running configuration file.

• show running-config interface fastethernet 0/1: Displays current configuration of specified interface

– show startup-config: Displays the saved configuration located in NVRAM.

– show interfaces: Statistics for all router interfaces.

• show interfaces fastethernet 0/1: Displays statistics for the specific interface on that slot/port number.

– show ip interfaces brief: Shows configured IP information and status for all router interfaces.

– show protocols: Displays the global and interface-specific status of any configured Layer 3 protocols.

– show arp: Displays the ARP table of the router.

Configuring an Interface

• Interfaces are configured in interface config mode, accessed via global config mode.

– Sydney# configure terminal

– Sydney(config)# interface serial 0/1

– Sydney(config-if)#

• Once an interface has been selected, specify a network address and subnet mask.

– Sydney(config-if)# ip address

• If the interface is a serial interface and is to be a DCE device, provide a clocking signal.

– Sydney(config-if)# clock rate 64000

• Lastly, administratively enable the interface.

– Sydney(config-if)# no shutdown

Saving Configuration Changes

Please Explain?

• Add descriptions and information where possible to help router usage and administration.

• Interface Descriptions should provide clear and specific information about the interface, eg. what department, building it services.

• Login Banners can be seen by anyone who attempts to login to a router.

– Should warn off unauthorised users!

– Can be used to inform users of router downtime.

Resolving Host Names

• Devices can use host names instead of IP addresses, provided a host table is configured.

• A host table associates host names with IP addresses

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

Get Backed Up

• Just as with servers, router files can be backed up for security and recovery purposes.

– Config files can be backed up to a network server, TFTP server, or to disk.

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