You have seen the configurable components, bootup sequence, and basic command modes of a Cisco router.
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Routers have an asynchronous serial port allowing local access to the router using a console terminal. Routers also have an auxiliary port, allowing you to configure them remotely using a modem.

Configuration information can be supplied to a router using

  • tftp servers

  • virtual terminals

  • network management stations

The internal configuration components of a router include

  • ROM and flash memory

  • RAM and NVRAM

  • Interfaces

There are three places to find the Cisco IOS image to load:

  • from flash memory

  • from a tftp server on the network

  • from ROM

For security purposes the Cisco IOS provides two levels of access to commands:

  • user EXEC mode

  • privileged EXEC mode
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You have seen how to log in to a Cisco router and how to examine its configurable components.
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You log in to the router by pressing Return at
the console. When you first log in you see a 
user EXEC mode prompt.

You enter Privileged EXEC mode using the 
Enable command.  The Privileged mode prompt 
is displayed while you are in this mode.

You can use several Cisco IOS commands to 
examine the status of a router. Each command 
allows you to examine a different configurable 
component of the router.

Examples of these commands include

  • show version

  • show processes

  • show flash

  • show memory

  • show interfaces

  • show protocols
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You have been introduced to Cisco router configuration.
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The Cisco AutoInstall procedure allows you to 
configure a router automatically and remotely 
over the network.

The new router must be connected to an existing 
router on either a WAN or a LAN link.

When you switch on a Cisco router, it goes through 
an initialization sequence to load the operating 
system and configuration file.

If no configuration file is found, and you are not 
using AutoInstall, the router enters Setup mode, 
prompting you for an initial configuration. This 
is called the system configuration dialog.

There are two principal configurations associated 
with each router:

  • startup configuration

  • running configuration

You can configure a router from a virtual (remote) 
terminal or from the console terminal.

You can enter multiple boot system commands in 
the router's startup configuration file to provide 
a backup method for loading a system image into 
the router.

You can create a backup of the Cisco IOS image by copying it to a network server.

You can approach router configuration with a general method.

Initially, you make certain changes to the router's configuration by entering commands in the appropriate configuration mode. Then you examine the results of the changes you have made. You use the Show Running-Config command to do this.

If the results are satisfactory you save them to the file that the router will use when it starts up again.Otherwise you can reverse the changes.
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You have seen how to access remote Cisco routers.
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The Cisco Discovery Protocol (CDP) enables you to 
access configuration information on other directly 
connected routers.

CDP runs by default when a router boots up.

You use the Show CDP Entry command to display a 
single cached CDP entry.

You use the Show CDP Neighbors command to 
display the CDP updates received on the local router.

You can use the TCP/IP remote login utility, Telnet, 
to initiate console sessions with remote routers.

If the target router's host name is available on 
the source router or if it can be reached from a 
DNS server to which the source router has access, 
then you access the target router using

  • the host name with the Telnet command

  • the host name alone

It is a good idea to perform basic testing of 
internetwork connectivity following the layers of 
the OSI model.

The Telnet, Trace, and Ping commands can be 
used to test links at different layers.
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