Router LED indicators
2.2.2 This page will explain how routers use LED indicators.
Cisco routers use LED indicators to provide status information. LED indicators will vary for different Cisco router models.
An interface LED indicates the activity of the corresponding interface. A problem may be indicated if an LED is off when the interface is active and the interface is correctly connected. If an interface is extremely busy, its LED will always be on. The green OK LED to the right of the AUX port will be on after the system initializes correctly.
The next page will examine the initial router bootup
The initial router bootup
2.2.3 This page will discuss the information and messages that are displayed during the initial router bootup. This information will vary, depending on the interfaces in the router and the Cisco IOS release. The screens displayed on this page are for reference only and may not reflect what the screen displays on the console.
In Figure , the statement “NVRAM invalid, possibly due to write erase”, tells the user that this router has not been configured yet or that the NVRAM has been erased. In order for the NVRAM to be valid after a router is configured and the configuration file is saved to NVRAM, the router must be configured to use the NVRAM configuration file. The factory-default setting for the configuration register is 0x2102, which indicates that the router should attempt to load a Cisco IOS image from flash memory.
In Figure , the user can determine the bootstrap version and the IOS version the router is using as well as the router model, processor, and the amount of memory the router contains. The figure also includes the following information:
• The number of interfaces
• The types of interfaces
• The amount of NVRAM
• The amount of flash memory
In Figure , the user has the option to enter setup mode. Remember, the primary purpose of the setup mode is to permit an administrator to install a basic router configuration when it cannot be obtained from another source.
The next page will teach students how to establish a console session with a router.
Sunday, May 2, 2010
Initial startup of Cisco routers
Initial startup of Cisco routers
2.2.1 This page will explain the startup process for Cisco routers.
A router initializes by loading the bootstrap, the operating system, and a configuration file. If the router cannot find a configuration file, it enters setup mode. Upon completion of the setup mode, a backup copy of the configuration file may be saved to NVRAM.
The goal of the startup routines for Cisco IOS software is to start the router operations. To do this, the startup routines must accomplish the following:
• Verify that the router hardware is tested and functional.
• Find and load the Cisco IOS software.
• Find and apply the startup configuration file or enter the setup mode.
When a Cisco router powers up, it performs a power-on self test (POST). During this self test, the router executes diagnostics from ROM on all hardware modules. These diagnostics verify the basic operation of the CPU, memory, and network interface ports. After verifying the hardware functions, the router proceeds with software initialization.
After the POST, the following events occur as the router initializes:
1. The generic bootstrap loader in ROM executes. A bootstrap is a simple set of instructions that tests hardware and initializes the IOS for operation.
2. The IOS can be found in several places. The boot field of the configuration register determines the location that is used to load the IOS. If the boot field indicates a flash or network load, boot system commands in the configuration file indicate the exact name and location of the image.
3. The operating system image is loaded. When the IOS is loaded and operational, a listing of the available hardware and software components is sent to the console terminal screen.
4. The configuration file saved in NVRAM is loaded into main memory and executed one line at a time. The configuration commands start routing processes, supply addresses for interfaces, and define other operating characteristics of the router.
5. If no valid configuration file exists in NVRAM, the operating system searches for an available TFTP server. If no TFTP server is found, the setup dialog is initiated.
Setup mode is not intended to be used to enter complex protocol features in a router. The purpose of the setup mode is to permit administrators to install a basic configuration for routers when a configuration cannot be obtained from another source.
In the setup mode, default answers appear in square brackets [ ] following the question. Press the Enter key to use these defaults. During the setup process, Ctrl-C can be pressed at any time to terminate the process. When Ctrl-C is used to terminate setup, all interfaces are administratively shut down.
When the configuration process is completed in setup mode, the following options will be displayed:
[0] Go to the IOS command prompt without saving this config.
[1] Return back to the setup without saving this config.
[2] Save this configuration to nvram and exit. Enter your selection [2]:
The next page will discuss router LED indicators.
2.2.1 This page will explain the startup process for Cisco routers.
A router initializes by loading the bootstrap, the operating system, and a configuration file. If the router cannot find a configuration file, it enters setup mode. Upon completion of the setup mode, a backup copy of the configuration file may be saved to NVRAM.
The goal of the startup routines for Cisco IOS software is to start the router operations. To do this, the startup routines must accomplish the following:
• Verify that the router hardware is tested and functional.
• Find and load the Cisco IOS software.
• Find and apply the startup configuration file or enter the setup mode.
When a Cisco router powers up, it performs a power-on self test (POST). During this self test, the router executes diagnostics from ROM on all hardware modules. These diagnostics verify the basic operation of the CPU, memory, and network interface ports. After verifying the hardware functions, the router proceeds with software initialization.
After the POST, the following events occur as the router initializes:
1. The generic bootstrap loader in ROM executes. A bootstrap is a simple set of instructions that tests hardware and initializes the IOS for operation.
2. The IOS can be found in several places. The boot field of the configuration register determines the location that is used to load the IOS. If the boot field indicates a flash or network load, boot system commands in the configuration file indicate the exact name and location of the image.
3. The operating system image is loaded. When the IOS is loaded and operational, a listing of the available hardware and software components is sent to the console terminal screen.
4. The configuration file saved in NVRAM is loaded into main memory and executed one line at a time. The configuration commands start routing processes, supply addresses for interfaces, and define other operating characteristics of the router.
5. If no valid configuration file exists in NVRAM, the operating system searches for an available TFTP server. If no TFTP server is found, the setup dialog is initiated.
Setup mode is not intended to be used to enter complex protocol features in a router. The purpose of the setup mode is to permit administrators to install a basic configuration for routers when a configuration cannot be obtained from another source.
In the setup mode, default answers appear in square brackets [ ] following the question. Press the Enter key to use these defaults. During the setup process, Ctrl-C can be pressed at any time to terminate the process. When Ctrl-C is used to terminate setup, all interfaces are administratively shut down.
When the configuration process is completed in setup mode, the following options will be displayed:
[0] Go to the IOS command prompt without saving this config.
[1] Return back to the setup without saving this config.
[2] Save this configuration to nvram and exit. Enter your selection [2]:
The next page will discuss router LED indicators.
Operation of Cisco IOS software
Operation of Cisco IOS software
2.1.5 This page will introduce the three distinct operating environments, or modes, of Cisco IOS devices:
The Cisco IOS devices have three distinct operating environments or modes:
• ROM monitor
• Boot ROM
• Cisco IOS
At startup, a Cisco router normally loads into RAM and executes one of these operating environments. A system administrator can use the configuration register setting to control the default startup mode for a router.
The ROM monitor performs the bootstrap process and provides low-level functionality and diagnostics. It is used to recover from system failures and to recover a lost password. The ROM monitor cannot be accessed through any of the network interfaces. It can only be accessed by way of a direct, physical connection through the console port.
When the router is running in boot ROM mode, only a limited subset of the Cisco IOS feature set is available. Boot ROM allows write operations to flash memory and is used primarily to replace the Cisco IOS image that is stored in flash. The Cisco IOS image can be modified in boot ROM with the copy tftp flash command. This command copies an IOS image that is stored on a TFTP server into the flash memory of a router.
The normal operation of a router requires use of the full Cisco IOS image as stored in flash. In some devices, the IOS is executed directly from flash. However, most Cisco routers require a copy of the IOS to be loaded into RAM and also executed from RAM. Some IOS images are stored in flash in a compressed format and have to be expanded when copied to RAM.
To see the IOS image and version that is running, use the show version command, which also indicates the configuration register setting. The show flash command is used to verify that the system has sufficient memory to load a new Cisco IOS image.
This page concludes the discussion about Cisco IOS. The next lesson will describe the initial startup of Cisco routers.
2.1.5 This page will introduce the three distinct operating environments, or modes, of Cisco IOS devices:
The Cisco IOS devices have three distinct operating environments or modes:
• ROM monitor
• Boot ROM
• Cisco IOS
At startup, a Cisco router normally loads into RAM and executes one of these operating environments. A system administrator can use the configuration register setting to control the default startup mode for a router.
The ROM monitor performs the bootstrap process and provides low-level functionality and diagnostics. It is used to recover from system failures and to recover a lost password. The ROM monitor cannot be accessed through any of the network interfaces. It can only be accessed by way of a direct, physical connection through the console port.
When the router is running in boot ROM mode, only a limited subset of the Cisco IOS feature set is available. Boot ROM allows write operations to flash memory and is used primarily to replace the Cisco IOS image that is stored in flash. The Cisco IOS image can be modified in boot ROM with the copy tftp flash command. This command copies an IOS image that is stored on a TFTP server into the flash memory of a router.
The normal operation of a router requires use of the full Cisco IOS image as stored in flash. In some devices, the IOS is executed directly from flash. However, most Cisco routers require a copy of the IOS to be loaded into RAM and also executed from RAM. Some IOS images are stored in flash in a compressed format and have to be expanded when copied to RAM.
To see the IOS image and version that is running, use the show version command, which also indicates the configuration register setting. The show flash command is used to verify that the system has sufficient memory to load a new Cisco IOS image.
This page concludes the discussion about Cisco IOS. The next lesson will describe the initial startup of Cisco routers.
Cisco IOS software features
Cisco IOS software features
2.1.4 This page will introduce some IOS images that are provided by Cisco for devices that span a wide range of network product platforms.
Cisco continues to develop different IOS software images to optimize the Cisco IOS software that these various platforms require. Each image represents a different feature set that serves the various device platforms, available memory resources, and customer needs.
Although there are numerous IOS images for different Cisco device models and feature sets, the basic configuration command structure is the same. The configuration and troubleshooting skills that are acquired for any device will apply to a wide range of products.
The naming convention for the different Cisco IOS releases contains three parts:
• The platform on which the image runs
• The special features supported in the image
• Where the image runs and whether it has been zipped or compressed
One of the main considerations when selecting a new IOS image is compatibility with the router flash and RAM memory. In general, the newer the release and the more features that it provides, the more flash and RAM memory it requires. Use the show version command on the Cisco device to check the current image and available flash.
The Cisco support site has tools available to help determine the amount of flash and RAM required for each image. For example, specific IOS features can be selected using the Cisco Software Advisor, which is available to registered Cisco.com users. The Cisco Software Advisor is an interactive tool that provides the most current information and allows users to select options that meet network requirements.
Before installing a new Cisco IOS software image on the router, check to see if the router meets the RAM memory and flash requirements for that image. To see the amount of RAM, issue the show version command:
…
2.1.4 This page will introduce some IOS images that are provided by Cisco for devices that span a wide range of network product platforms.
Cisco continues to develop different IOS software images to optimize the Cisco IOS software that these various platforms require. Each image represents a different feature set that serves the various device platforms, available memory resources, and customer needs.
Although there are numerous IOS images for different Cisco device models and feature sets, the basic configuration command structure is the same. The configuration and troubleshooting skills that are acquired for any device will apply to a wide range of products.
The naming convention for the different Cisco IOS releases contains three parts:
• The platform on which the image runs
• The special features supported in the image
• Where the image runs and whether it has been zipped or compressed
One of the main considerations when selecting a new IOS image is compatibility with the router flash and RAM memory. In general, the newer the release and the more features that it provides, the more flash and RAM memory it requires. Use the show version command on the Cisco device to check the current image and available flash.
The Cisco support site has tools available to help determine the amount of flash and RAM required for each image. For example, specific IOS features can be selected using the Cisco Software Advisor, which is available to registered Cisco.com users. The Cisco Software Advisor is an interactive tool that provides the most current information and allows users to select options that meet network requirements.
Before installing a new Cisco IOS software image on the router, check to see if the router meets the RAM memory and flash requirements for that image. To see the amount of RAM, issue the show version command:
…
Router user interface modes
Router user interface modes
2.1.3 This page will introduce two user interface modes that can be configured for Cisco IOS.
The Cisco CLI uses a hierarchical structure. This structure requires entry into different modes to accomplish particular tasks. For example, to configure a router interface, the user must enter interface configuration mode. All configurations that are entered in interface configuration mode apply only to that interface. Each configuration mode is indicated with a distinctive prompt and allows only commands that are appropriate for that mode.
The IOS provides a command interpreter service known as the command executive (EXEC). After each command is entered, the EXEC validates and executes the command.
As a security feature the Cisco IOS software separates the EXEC sessions into two access levels. These levels are user EXEC mode and privileged EXEC mode. The privileged EXEC mode is also known as enable mode. The following are the features of the user EXEC mode and privileged EXEC mode:
• The user EXEC mode allows only a limited number of basic monitoring commands. This is often referred to as a view only mode. The user EXEC level does not allow any commands that might change the configuration of the router. The user EXEC mode can be identified by the > prompt.
• The privileged EXEC mode provides access to all router commands. This mode can be configured to require a password. For added protection, it can also be configured to require a user ID. This allows only authorized users to access the router. Configuration and management commands require that the network administrator be at the privileged EXEC level. Global configuration mode and all other more specific configuration modes can only be reached from the privileged EXEC mode. The privileged EXEC mode can be identified by the # prompt.
To access the privileged EXEC level from the user EXEC level, enter the enable command at the > prompt. If a password is configured, the router will then ask for that password. For security reasons, a Cisco network device will not show the password that is entered. When the correct password is entered, the router prompt will change to #. This indicates that the user is at the privileged EXEC level. When a question mark, ?, is entered at the privileged EXEC level, it will reveal many more command options than available at the user EXEC level.
The next page covers some additional features of Cisco IOS.
2.1.3 This page will introduce two user interface modes that can be configured for Cisco IOS.
The Cisco CLI uses a hierarchical structure. This structure requires entry into different modes to accomplish particular tasks. For example, to configure a router interface, the user must enter interface configuration mode. All configurations that are entered in interface configuration mode apply only to that interface. Each configuration mode is indicated with a distinctive prompt and allows only commands that are appropriate for that mode.
The IOS provides a command interpreter service known as the command executive (EXEC). After each command is entered, the EXEC validates and executes the command.
As a security feature the Cisco IOS software separates the EXEC sessions into two access levels. These levels are user EXEC mode and privileged EXEC mode. The privileged EXEC mode is also known as enable mode. The following are the features of the user EXEC mode and privileged EXEC mode:
• The user EXEC mode allows only a limited number of basic monitoring commands. This is often referred to as a view only mode. The user EXEC level does not allow any commands that might change the configuration of the router. The user EXEC mode can be identified by the > prompt.
• The privileged EXEC mode provides access to all router commands. This mode can be configured to require a password. For added protection, it can also be configured to require a user ID. This allows only authorized users to access the router. Configuration and management commands require that the network administrator be at the privileged EXEC level. Global configuration mode and all other more specific configuration modes can only be reached from the privileged EXEC mode. The privileged EXEC mode can be identified by the # prompt.
To access the privileged EXEC level from the user EXEC level, enter the enable command at the > prompt. If a password is configured, the router will then ask for that password. For security reasons, a Cisco network device will not show the password that is entered. When the correct password is entered, the router prompt will change to #. This indicates that the user is at the privileged EXEC level. When a question mark, ?, is entered at the privileged EXEC level, it will reveal many more command options than available at the user EXEC level.
The next page covers some additional features of Cisco IOS.
Router user interface
Router user interface
2.1.2 This page will review the Cisco IOS. The IOS is a core technology that extends across most of the Cisco product line. Its operation details may vary on different internetworking devices.
The CLI environment can be accessed several ways. Typically, the CLI is accessed through a console session. A console uses a low speed serial connection directly from a computer or terminal to the console connection on the router. A CLI session can also be accessed remotely through a dialup connection using a modem connected to the router AUX port. Neither of these methods require that the router have any IP services configured. A third method of accessing a CLI session is to Telnet to the router. To establish a Telnet session to the router, at least one interface must be configured with an IP address, and virtual terminal sessions must be configured for login and passwords.
The next page discusses the different user modes that are available for Cisco IOS.
2.1.2 This page will review the Cisco IOS. The IOS is a core technology that extends across most of the Cisco product line. Its operation details may vary on different internetworking devices.
The CLI environment can be accessed several ways. Typically, the CLI is accessed through a console session. A console uses a low speed serial connection directly from a computer or terminal to the console connection on the router. A CLI session can also be accessed remotely through a dialup connection using a modem connected to the router AUX port. Neither of these methods require that the router have any IP services configured. A third method of accessing a CLI session is to Telnet to the router. To establish a Telnet session to the router, at least one interface must be configured with an IP address, and virtual terminal sessions must be configured for login and passwords.
The next page discusses the different user modes that are available for Cisco IOS.
Module 2: Introduction to Routers / Overview / The purpose of Cisco IOS software
Module 2: Introduction to Routers
Overview: Cisco technology is based on the Cisco IOS, which is the software that controls the routing and switching functions of network devices. A solid understanding of the IOS is essential for a network administrator. This module will introduce the main features of the IOS and will provide practice in working with the IOS. All network configuration tasks, from the most basic to the most complex, require a strong foundation in the basics of router configuration. This module will provide the tools and techniques for basic router configuration that will be used throughout this course.
This module covers some of the objectives for the CCNA 640-801, INTRO 640-821, and ICND 640-811 exams. -
Students who complete this module should be able to perform the following tasks:
• Describe the purpose of the IOS
• Describe the basic operation of the IOS
• Identify various IOS features
• Identify the methods to establish a command-line interface (CLI) session with the router
• Alternate between the user executive (EXEC) and privileged EXEC modes
• Establish a HyperTerminal session on a router
• Log into a router
• Use the help feature in the command line interface
• Troubleshoot command errors
The purpose of Cisco IOS software
2.1.1 As with a computer, a router or switch cannot function without an operating system. This page will review the Cisco IOS. It is the embedded software architecture in all of the Cisco routers and is also the operating system of the Catalyst switches. Without an operating system, the hardware does not have any capabilities. The Cisco IOS provides the following network services:
• Basic routing and switching functions
• Reliable and secure access to networked resources
• Network scalability
The next page will discuss the Cisco IOS environment for a router.
Overview: Cisco technology is based on the Cisco IOS, which is the software that controls the routing and switching functions of network devices. A solid understanding of the IOS is essential for a network administrator. This module will introduce the main features of the IOS and will provide practice in working with the IOS. All network configuration tasks, from the most basic to the most complex, require a strong foundation in the basics of router configuration. This module will provide the tools and techniques for basic router configuration that will be used throughout this course.
This module covers some of the objectives for the CCNA 640-801, INTRO 640-821, and ICND 640-811 exams. -
Students who complete this module should be able to perform the following tasks:
• Describe the purpose of the IOS
• Describe the basic operation of the IOS
• Identify various IOS features
• Identify the methods to establish a command-line interface (CLI) session with the router
• Alternate between the user executive (EXEC) and privileged EXEC modes
• Establish a HyperTerminal session on a router
• Log into a router
• Use the help feature in the command line interface
• Troubleshoot command errors
The purpose of Cisco IOS software
2.1.1 As with a computer, a router or switch cannot function without an operating system. This page will review the Cisco IOS. It is the embedded software architecture in all of the Cisco routers and is also the operating system of the Catalyst switches. Without an operating system, the hardware does not have any capabilities. The Cisco IOS provides the following network services:
• Basic routing and switching functions
• Reliable and secure access to networked resources
• Network scalability
The next page will discuss the Cisco IOS environment for a router.
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