Cisco Memory Components
- Select the components required to meet a network specification
- Describe the purpose and functions of various network devices
Four memory components are used by Cisco devices. Those components include ROM, Flash, RAM, and NVRAM.
Read-only memory (ROM) contains the basic code for booting a device and maintaining Power on Self Test (POST), ROM Monitor (ROMmon), bootstrap, and RXBOOT. Because this type of memory is read-only, it cannot be changed by any configuration done at the networking device. ROM is nonvolatile, so data is not lost when the device is powered off.
Flash is installed on either an electrically erasable, programmable, read-only memory (EEPROM) or Personal Computer Memory Card International Association (PCMCIA) card. Flash memory contains the Cisco Internetworking Operating System (IOS) image. The router uses Flash by default to locate the IOS when it is booted. Configuration files may also be stored on a Flash card. Like ROM, Flash is also nonvolatile memory.
Random-access memory (RAM) is used for short-term storage of a machine’s running IOS and running configuration. The IOS is copied from Flash to RAM. This is the only type of system memory that is not permanent. At times, you may hear RAM also referred to as dynamic random-access memory (DRAM). Because this type of memory is volatile, it is lost whenever the machine is shut down.
RAM contains the running IOS, with the exception of Run-From-Flash (RFF) routers. RAM also contains the running configuration or the active configuration that is used after a machine is booted.
Nonvolatile random-access memory (NVRAM) stores the startup configuration. This is the configuration that is loaded when the machine is booted.
Cisco Internetworking Operating System
Cisco IOS software is developed and maintained by Cisco to support a full array of system functions, applications (including Internet applications), and network hardware in a single software package. IOS software is installed on each Cisco router or switch and can accommodate network growth and provide for secure data transfers. The command-line interface (CLI) for routers and switches defines the commands that are used to communicate with the IOS. Future chapters demonstrate the use of CLI commands on both network devices.
A Cisco Catalyst switch may use either a Cat OS or Cisco IOS. The major difference with Cat OS is the CLI commands that are used in conjunction with the operating system software.
Cisco releases IOS software using what they call trains. Each release can be further defined by train identifiers. A train identifier determines whether a release is a Technology (T), Enterprise, or Service Provider (SP) release. When the IOS version has no train identifier, it is the mainline train. With so many features and applications being offered with each release, a train identifier can further define a specific subset of features. For example, if you have a release named 12.3(1)T, the IOS version number breaks down as follows:
- 12.3 refers to the mainline train that will not be added to but will be subject to IOS bug fixes.
- (1) represents the release number, which increments with each new release of the mainline train.
- T identifies the type of train release where T stands for Technology. This may also be an S (Service Provider) or E (Enterprise) train.
A feature set is a package of the features that is offered in addition to the basic IOS functions of an IOS software release. You can select more than one feature set per release. Feature sets may be identified as standard, enhanced, or advanced, depending on the services that are supported. To give you an idea of the latest features available with Cisco IOS, current releases offer the following software functionality:
- IP Base—The base IOS image.
- IP Voice—Features include Voice over IP (VoIP), and Voice over Frame (VoFR).
- Advanced Security—Offers advanced protection via firewall, Intrusion Detection System (IDS), Secure Shell (SSH), and IP Security (IPSec).
- SP Services—Includes service provider services such as IPv6, Netflow SSH, ATM, Voice over ATM (VoATM), and Frame Relay.
- Enterprise Base—Consists of Enterprise Layer 3 routed protocols, and IBM support.
- Advanced IP Services—Offers a combination of the Advanced Security and Service Provider Services feature sets.
- Enterprise Services—Combines the Enterprise Base and Service Provider Services feature sets with full IBM support.
- Advanced Enterprise Services—Incorporates all the Cisco IOS feature sets.
IOS Image File Naming
The IOS image file represents the name of the system image on a Cisco router or switch. The hardware platform, feature set, compression format, IOS version, and train information are all found in the name of an IOS image file. An IOS image filename can be broken out to identify more specific information about the IOS in use by a device. This is helpful if you are troubleshooting a system issue and need to verify what version is currently in use. Cisco may be aware of an IOS bug, or the version may simply be outdated and an IOS upgrade might be the solution to your trouble. To find the IOS image filename, use the show version command from the command prompt.
Given the example filename c2600-ipbase-1.122-1.T.bin (.bin indicates binary format), from left to right, each portion of the filename represents the following:
- c2600—Hardware platform (Cisco 2600 router)
- ipbase—Feature set
- 1 —File format (compressed re-locatable)
- 122—IOS version number
- 1 —Maintenance release number
- T—Train identifier
Remember the IOS image file structure. If given a filename, you should be able to break down each part of the file and what it represents.