Module 6: Routing and Routing Protocols / Overview

Module 6: Routing and Routing Protocols
Overview

Routing is a set of directions to get from one network to another. These directions, also known as routes, can be dynamically given to the router by another router, or they can be statically assigned to the router by an administrator.
This module introduces the concept of dynamic routing protocols, describes the classes of dynamic routing protocols, and gives examples of protocols in each class.
A network administrator chooses a dynamic routing protocol based upon many considerations. These include the size of the network, the bandwidth of available links, the processing power of the routers, the brands and models of the routers, and the protocols that are used in the network. This module will provide more details about the differences between routing protocols that help network administrators make a choice.
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:

• Explain the significance of static routing
• Configure static and default routes
• Verify and troubleshoot static and default routes
• Identify the classes of routing protocols
• Identify distance vector routing protocols
• Identify link-state routing protocols
• Describe the basic characteristics of common routing protocols
• Identify interior gateway protocols
• Identify exterior gateway protocols

Enable Routing Information Protocol (RIP) on a router

Module 5 : Summary

Summary

This page summarizes the topics discussed in this module. The default configuration register setting can be changed with the global configuration mode command config-register. The boot sequence for the Cisco IOS can specify the fallback sequence that is used to boot Cisco IOS software. A common fallback sequence would be to load first from flash memory, which is not vulnerable to network failures. The network server would be used next if the flash memory were corrupt. Finally if the first two methods failed the router would boot from ROM. However, the system image in ROM will likely be a subset of the full Cisco IOS image. The command copy running-config startup-config saves the configuration commands in NVRAM. The router will execute the boot system commands as needed in the order in which they were originally entered in the configuration mode. If a configuration register setting is incorrect, the Cisco IOS will not load from flash. To troubleshoot the boot sequence, 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 form of the command to delete the statement. The two types of software required to operate a router and a switch are the operating systems and the configuration. The Cisco IOS allows the hardware to function. The configuration file or config is the software that contains the instructions that define how the device is to route or switch the packets that enter the device. The naming convention for Cisco IOS files includes four parts. The first part of the Cisco IOS file name identifies the hardware platform for which this image is designed. The second part of the Cisco IOS file name identifies the various features that this file contains. The third part of the file name indicates the file format. It specifies if the Cisco IOS is stored in flash in a compressed format and whether it is relocatable. The fourth part of the file name identifies the release of the Cisco IOS. As newer versions of the Cisco IOS are developed, the numerical version number increases. The active configuration for a Cisco router is maintained in RAM and the default location for the startup configuration is NVRAM. The copy running-config tftp command can be used to back up copies of the configuration to a TFTP server. Another way to create a backup copy of the configuration is to capture the output of the show running-config command. To do this from the terminal session, copy the output, paste it to a text file, and then save the text file. After the capture is complete, the configuration file needs to be edited to remove extra text. To add a comment, begin a line with an exclamation mark (!).

File system verification

File system verification

5.2.8

This page will review some commands that can be used to verify the router file system. One of these is the show version command. The show version command can be used to check the current image and the total amount of flash. It also verifies two other items that relate to how the IOS is loaded. It identifies the source of the IOS image that the router used to boot and displays the configuration register. Check the boot field setting of the configuration register to determine the location from which the router will load the IOS. If these do not agree, there may be a corrupt or missing IOS image in flash or there may be boot system commands in the startup configuration. The show flash command can also be used to verify the file system. This command is used to identify IOS images in flash and the amount of flash that is available. This command is often used to confirm that there is ample space to store a new IOS image. As previously mentioned, the configuration file may contain boot system commands. These commands can be used to identify the source of the desired IOS boot image. Multiple boot system commands may be used to create a fallback sequence to discover and load an IOS. These boot system commands will be processed in the order of their appearance in the configuration file. This page concludes this lesson. The next page will summarize the main points from this module.

Environment variables

Environment variables

5.2.7

This page will explain what the ROMmon environment variables are and how they are used.
The IOS can also be restored from a TFTP session. The fastest way to restore an IOS image to the router is to use TFTP from ROMmon to download the image. To do this, set the environmental variables and then use the tftpdnld command.
Since the ROMmon has very limited functions, no configuration file is loaded during boot. As a result, the router has no IP or interface configuration. The environmental variables provide a minimal configuration to allow for the TFTP of the IOS. The ROMmon TFTP transfer works only on the first LAN port so a simple set of IP parameters are set for this interface. To set a ROMmon environment variable, type the variable name, then the equal sign (=), and the value for the variable. For example, to set the IP address to 10.0.0.1, type IP_ADDRESS=10.0.0.1 at the ROMmon prompt. 

Note: All variable names are case sensitive.

The minimum variables required to use tftpdnld are as follows:

• IP_ADDRESS - The IP address on the LAN interface
• IP_SUBNET_MASK - The subnet mask for the LAN interface
• DEFAULT_GATEWAY - The default gateway for the LAN interface
• TFTP_SERVER - The IP address of the TFTP server
• TFTP_FILE - The IOS filename on the server

Use the set command to check the ROMmon environment variables. 
Once the variables are set for the IOS download, the tftpdnld command is entered with no arguments. The ROMmon will echo the variables and then a confirmation prompt will appear with a warning that this will erase the flash. 
As each datagram of the IOS file is received, an exclamation point (!) will be displayed. When the complete IOS file has been received, the flash will be erased and the new IOS image file written. Appropriate messages will be displayed as the process is completed.
When the new image is written into flash and the ROMmon prompt is displayed, the router can be restarted by entering the reset command or typing i. The router should now boot from the new IOS image in flash.
The next page will describe some commands that can be used to verify a router file system.