A-9
CiscouBR924 Software Configuration Guide
OL-0337-05 (8/2002)
AppendixA Using Cisco IOS Software
Understanding Cisco IOS Configuration Files
ubr924>show ip traffic | include error
0 format errors, 0 checksum errors, 1 bad hop count
Rcvd: 0 format errors, 0 checksum errors, 0 redirects, 4 unreachable
Total: 0/0, 0 checksum errors, 0 format errors
Total: 0/0, Format errors: 0/0, Checksum errors: 0/0
Rcvd: 134 total, 0 checksum errors
Rcvd: 23 total, 0 checksum errors, 9 no port
Rcvd: 17 total, 0 checksum errors, 1 no port
Understanding Cisco IOS Configuration Files
Cisco IOS configuration files are text files that contain Cisco IOS commands to configure the
CiscouBR924 router when it boots up and is first configured. These commands are the same commands
that could be given manually at the router’s CLI interface; however, putting them in a configuration file
avoids having to retype them whenever the router is reset.

Downloading the Configuration File

Usually, the Cisco IOS configuration file is specified as part of the DOCSIS configuration file. In this
situation, the service provider creates and maintains both the DOCSIS and Cisco IOS configuration files
for the routers, and those files are stored on TFTP servers located at the provider’s headend plant.
The Cisco uBR924 router automatically loads the DOCSIS configuration file when it is connected to a
cable network and powered on. If the DOCSIS configuration file specifies that a C isco IOS configuration
file is to be loaded, the router uses the TFTP protocol to download that file and then executes the file so
that the non-DOCSIS routing and interface parameters are correctly configured.
When the DOCSIS configuration file specifies that a Cisco IOS configuration file should be downloaded,
the Cisco uBR924 router automatically takes the following steps to ensure that the configuration cannot
be changed by the user at the remote site:
1. Terminates any current Telnet sessions.
2. Disables console access.
3. Deletes the current Cisco IOS configuration, if any.
4. Downloads the Cisco IOS configuration file.
5. After configuring itself according to the commands in the Cisco IOS configuration file, the router
comes online and starts sending traffic.
If the DOCSIS configuration file does not specify that a Cisco IOS configuration file should be loa ded,
the network administrator can log in to the router’s CLI interface and manually load the file using the
copy tftp command. (In this situation, console access is not disabled, allowing users at the remote site
to modify the configuration if desired.)
Note The DOCSIS configuration file is a binary file that must be in the specific format given by the DOCSIS
1.0 specification; it configures DOCSIS and cable-related parameters. The Cisco IOS configuratio n file
is a text file that can be in any arbitrary format, as long as the lines in that file contain valid commands
that could be given at the router’s CLI interface. Typically, the Cisco IOS configuration file sets routing
parameters and whatever other parameters are needed f or special feature sets, such as the voice over IP
(VoIP) or firewall features.