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Examining RAM, NVRAM, and Flash RAM

Several items reside in the router's RAM (while the router is powered on), including the router's active IOS, the running configuration, the routing table, and other cache and buffers (such as the History buffer). You can view these items using various permutations of the show command.

For example, to view the router's running configuration, you would use the show running-config command at the privileged prompt (see the following two figures—the results of the command are selectively shown).

Figure 3.7

Figure 3.8

This command provides configuration information (such as passwords and the banner for the router) and the current status of the router's interfaces.

Another useful command related to the router's RAM is the show version command. This enables you to view the version of the IOS that is currently running on the router.

RAM also provides the temporary storage area for your routing tables. Routing tables and routing IP and IPX are discussed later in this book. To view the current routing table for a network protocol such as IP, you would use the show ip route command. The following figure shows the results of this command. Routes labeled with a C are directly connected routes, whereas routes labeled with an R were learned by the routing protocol running on the router.

Figure 3.9

NVRAM supplies the nonvolatile storage area for your startup configuration. The output of the show startup-config command looks much the same as the running-config command displayed in the previous two figures. However, it can be different from that command, and it is also a privileged mode command.

Flash RAM is where the current image of the system IOS resides. If your router has enough Flash RAM, alternative versions of the IOS can also be stored there (other than the IOS image that's loaded when the router is powered on). This is useful in cases where you plan to upgrade the IOS on all your routers at once because the new IOS is immediately available for deployment.

To view the contents of the Flash RAM, use the command show flash. The next figure shows the results of this command.

Figure 3.10


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