The IOS naming convention

The IOS naming convention

5.2.2

This page will introduce the Cisco IOS naming convention. Students will learn why it is used and what each field represents.
There are many different versions of the Cisco IOS. The IOS supports varied hardware platforms and features. New versions of the IOS are continuously developed and released.
To identify the different versions, there is a naming convention for IOS files. This IOS naming convention uses different fields in the name. The fields include the hardware platform identification, the feature set identification, and the numerical release. 
The first part of the Cisco IOS file name identifies the hardware platform for which an image is designed.
The second part of the IOS file name identifies the various features that a file contains. There are many different features to choose from. These features are packaged in software images. Each feature set contains a specific subset of Cisco IOS features. Here are some examples of feature-set categories:

• Basic - A basic feature set for a hardware platform such as IP and IP/FW
• Plus - A basic feature set plus additional features such as IP Plus, IP/FW Plus, and Enterprise Plus
• Encryption - A 56-bit data encryption feature set, such as Plus 56, that is combined with a basic or plus feature set. Examples include IP/ATM PLUS IPSEC 56 or Enterprise Plus 56.

The encryption designators for Cisco IOS Release 12.2 or later are k8 and k9:

—k8 - Less than or equal to 64-bit encryption in IOS version 12.2 and later

—k9 - Greater than 64-bit encryption in IOS version 12.2 and later

The third part of the file name indicates the file format. It specifies if the IOS is stored in flash in a compressed format and whether the IOS is relocatable. If the flash image is compressed, the IOS must be expanded during boot as it is copied to RAM. A relocatable image is copied from flash into RAM to run. A non-relocatable image is run directly from flash.
The fourth part of the file name identifies the release of the IOS. The numerical version number increases for newer versions of the IOS.
The Interactive Media Activity will help students become familiar with the fields in an IOS image name.
The next page will show students how a TFTP server can be used to manage configuration files.

Managing the Cisco File System / IOS file system overview

Managing the Cisco File System

IOS file system overview

5.2.1

This page will introduce the Cisco IOS File System.
Routers and switches depend on software for their operation. The two types of software required are operating systems and configuration.
The operating system used in almost all Cisco devices is the Cisco IOS. The Cisco IOS is the software that allows the hardware to function as a router or switch. The IOS file is several megabytes.
The software a router or switch uses is referred to as the configuration file or the config. The configuration contains the instructions that define how the device is to route or switch. A network administrator creates a configuration that defines the desired functionality of a Cisco device. The functions that can be specified by the configuration are the IP addresses of the interfaces, routing protocols, and networks to be advertised. The configuration file typically is a few hundred to a few thousand bytes.
Each of the software components is stored in memory as a separate file. These files are also stored in different types of memory. 
The IOS is stored in a memory area called flash. Flash memory provides non-volatile storage of an IOS that can be used as an operating system at startup. The flash allows the IOS to be upgraded or stores multiple IOS files. In many router architectures, the IOS is copied into and run from RAM.
A copy of the configuration file is stored in NVRAM to be used during startup. This is referred to as the startup configuration or startup config. The configuration in RAM is used to operate a router. It is referred to as the running configuration or running config.
Version 12 and later releases of the IOS provide a single interface to all the file systems that a router uses. This is referred to as the Cisco IOS File System (IFS). The IFS provides a single method to perform all the file system management for a router. This includes the flash memory file systems, the network file systems, such as TFTP and FTP, and read or write data, such as NVRAM, the running configuration, and ROM. The IFS uses a common set of prefixes to specify file system devices. 
The IFS uses the URL convention to specify files on network devices and the network. The URL convention identifies the location of the configuration files following the colon as [[[//location]/directory]/filename]. The IFS also supports FTP file transfers.
The Interactive Media Activity will help students become familiar with the IFS configuration files and their locations.
The next page will describe the IOS naming conventions.

Troubleshooting IOS boot failure

Troubleshooting IOS boot failure

5.1.5 

This page will explain why a router may not boot properly and show students what to do when this occurs. There are several reasons that a router may not boot properly: Configuration file has missing or incorrect boot system statement Incorrect configuration register value Corrupted flash image Hardware failure When a router boots, it looks in the startup configuration file for a boot system statement. This boot system statement can force the router to boot from another image instead of the IOS in flash. Use the show version command to look for the line that identifies the boot image source. Use the show running-config command and look for a boot system statement near the top of the configuration. If the boot system statement points to an incorrect IOS image, use the no version of the command to delete the statement. If the configuration register setting is incorrect, the IOS cannot load from flash. The value in the configuration register tells the router where to get the IOS. To confirm this, use the show version command and look at the last line for the configuration register. The correct value varies for different hardware platforms. A part of the documentation of the internetwork should be a printed copy of the show version output. If that documentation is not available, there are resources on the Cisco documentation CD or Cisco website to identify the correct configuration register value. To correct this, change the configuration register and save this as the start-up configuration. If there is still a problem, the router may have a corrupted flash image file. If this is the case, an error message should be displayed during boot. That message may take one of several forms. Some examples are as follows: open: read error...requested 0x4 bytes, got 0x0 trouble reading device magic number boot: cannot open "flash:" boot: cannot determine first file name on device "flash:" If the flash image is corrupt, a new IOS should be uploaded into the router. If none of the above appears to be the problem, the router could have a hardware failure. If this occurs, contact the Cisco Technical Assistance Center (TAC). Although hardware failures are rare, they do occur. The value of the configuration register is not displayed by the show running-config or show startup-config commands. Students can use the Lab Activities to troubleshoot IOS boot failure and document configuration register settings. This page concludes this lesson. The next lesson will show students how to manage the Cisco IOS File System. The first page will give an overview of the IOS File System.