Router Overview - The Configuration File

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Managing a router involves installation, upgrades, backups, recovery, and other event-driven tasks, but the biggest part of router management is the care and feeding of a router’s configuration file. The configuration file is the cockpit from which the network administrator runs the router and all the traffic going through it. As will be detailed in the next chapter, configuration files contain access lists, passwords, and other important router management tools.

Viewing the Configuration File

The most common way to examine the status of a router is to view its configuration file. To view most anything in IOS is to ask for a view of the configuration. The main IOS command for viewing such information is the show command.

The following example uses the show running-config command to view a router’s running configuration. There are two types of configuration files. The runningconfiguration file is an image running in DRAM (main memory) at a given time. The backupconfiguration file is stored in NVRAM and is used to boot the router.

Router#show running-config
Building configuration...

Current configuration:
!
version 11.2
service password-encryption
service udp-small-servers
service tcp-small-servers
!
hostname Router
!
enable secret 5 $1$C/q2$ZhtujqzQIuJrRGqFwdwn71
enable password 7 0012000F
!
vty-async
!
interface Serial0
no ip address
no ip route-cache
no ip mroute-cache
shutdown
! interface Serial1
no ip address
.
.
.

In the next chapter we will go into greater depth on what the configuration file does and how to edit it.

Using TFTP for Configuration File Backups and Updates

As with IOS system image backups and updates, TFTP servers are used to back up and update configuration files. For example, the copy running-config tftp command is used to back up the router’s running configuration file (named tomtest in this example) to a TFTP server, using the following procedure:

Router#copy running-config tftp
Remote host []? 10.1.10.40
Name of configuration file to write [router-confg]? test
Write file tomtest on host 10.1.10.40? [confirm]<cr>
Building configuration...

Writing test !! [OK]
Router#

The other TFTP commands to back up or update configuration files are

▼ copy tftp running-config Configures the router directly by copying from the TFTP directly into the router’s DRAM

■ copy startup-config tftp Backs up the startup configuration from the router’s NVRAM to the TFTP server

▲ copy tftp startup-config Updates the router’s startup configuration file by downloading from the TFTP server and overwriting the one stored in the router’s NVRAM

Note that tftp goes in front of the file type—running-config or startup-config—to download (update from the server) and behind the file type to upload (back up to the server). Think of the copy command as copying from somewhere to somewhere.

This chapter is from Cisco: A Beginner's Guide, by Velte and Velte (McGraw-Hill/Osborne, 2004, ISBN: 0072256354). Check it out at your favorite bookstore today.  Buy this book now.

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