Your phone rings; it is not the news you want to hear.

The network is down, and it is your job to fix it.

What You’ll Learn

What You’ll Need

First, load the Packet Tracer file that has the initial topology.

Initial Topology

The network that we need to fix has three routers:

After a power outage, the network has stopped working. All three of these routers have problems that we need to fix.

Important: To simulate the power outage, click the Power Cycle Devices button in Packet Tracer in the bottom left-hand corner.

Power Cycle Button

After the devices reboot, you will then see the problems in the network. The goal is to fix all the issues and restore the configurations so that the routers can ping all loopbacks. You need to restore the configurations, without configuring the network.

Router R3 Initial Investigation

After power cycling the routers, look at the CLI for R3; you will notice it has the error message no valid BOOT image found. It then attempts to boot from the default boot device. We then get the error that test.bin is not accessible and cannot be loaded.

R3 not booting correctly

For some reason, the router R3 is trying to load test.bin and fails. It then tries to boot from the default boot device, which boots the isr4300-...SPA.bin operating system, and then the router boots up.

Why is the router trying to boot from the test.bin boot file and defaulting to another one?

Router R2 Initial Investigation

Router R2 is in ROMMON mode, which is a major issue. If you look at the prompt for the device, it says rommon 1. There are only a few options in ROMMON mode. Because the router has not booted from a valid operating system, it defaulted to ROMMON.

If we look at the topology, all the interfaces are down, which is a big problem.

Router R1 Initial Investigation

Router R1 prompts to enter the initial configuration dialogue. If you say no and enter into the router’s CLI, the router’s name is now simply Router instead of R1, and the show running-configuration has nothing but the default configuration of a new installation. The interfaces have no IP address and are shut down.

Can you fix the network without configuring anything, but just restoring what is already there?

We are now going to walk through how to fix the issues on router R1. When we rebooted the devices, R1 did not boot correctly. It ends up in the initial configuration dialogue with no configuration.

R1 not booting correctly

  1. Start by answering no to the initial configuration dialogue. We want the router to boot with the correct configuration.

  2. Enter enable mode and check the running configuration with a show run command. We can see the router has a default configuration and no routing protocol.

  3. Issue a show version command on R1; note that the system image file is fine. Hit the space bar a few more times to see at the bottom of the output that the configuration register of the router is 0x2142. That is a problem. Let’s see why:

  1. Issue a show startup-config command and compare the size of bytes (768 bytes) to the show running-configuration (564 bytes). The startup configuration has the original configuration that we need to restore the device to be fixed. You can review the configuration to verify it, but it is much larger, with the interface configuration, hostname R1, and EIGRP running.

Startup vs Running Config

Because the configuration register is incorrect, it is not loading the correct configuration, ignoring the NVRAM configuration (startup configuration), and boots as if it is a brand-new router. Using 0x2142 is useful if you need to do password recovery because you are able to boot in to the device and ignore that startup configuration. In this case, we do not need to do password recovery, so we want to set it back to 0x2102 to boot normally.

  1. Enter configuration mode with conf t, and configure config-register 0x2102 and end.

  2. Verify the config register is updated by issuing show version again and looking at the bottom of the output. It should update at the next reload.

  3. Reload the device with the reload command, but do not answer yes (as you usually do) to saving the configuration before the reload. We want to replace the running config with the startup config in this case. Configuration registers are stored in a separate location, so you do not need to save before reloading; it will load from the new config register on reload.

After the reload, you can verify that the configuration is there (password is cisco). If you issue a show ip interface brief command to verify, you will see the interfaces are UP / DOWN. That is because we have not restored the other routers yet.

When the router R2 rebooted, it entered ROMMON mode. Let’s see what that looks like.

  1. Use the ? to see the commands available.

R2 in ROMMON mode

Note that every time you type a command, the number next to the ROMMON prompt will increment by one. We have a command called confreg to help set the configuration register and reset to reboot the router.

  1. Use the command confreg 0x2102 to check to see if we can get the router to boot normally. Now, issue the reset command to reload the router.

Note: After the reload, check the topology and see the interfaces go green and a new EIGRP adjacency on R2.

R2 booting up after the changes

  1. Enter enable mode in R2, and issue a show ip interface brief command to check the status of the network. Notice that the interfaces are UP (for the device that has been fixed on the other side). Issue a show ip eigrp neighbor to see the neighbor relationships coming up with R1.

  2. Test the connection to R1 by issuing a ping to the loopback of R1 with ping 1.1.1.1. The ping should be successful at this point.

To simulate the problem we just saw, you can configure config-register 0x2100 to have the router boot in to ROMMON mode (after a reload and without saving the configuration).

Logging in to router R3 has the correct name at the prompt, but there is no password, which is incorrect.

  1. Issue a show ip interface brief and see that all the interfaces are down (ADMIN DOWN / DOWN) and there are no IP addresses assigned. Also, issue a show ip protocol and see that there are no routing protocols enabled on the router.

Note: If you remember from our initial troubleshooting, R3 was trying to load test.bin as the operating system image and failed.

  1. Let’s look at the boot images in storage with a show flash command. There is an isr4300...SPA.bin file in flash memory and no test.bin file. Trying to get the router to boot from test.bin will not work because there is no file with that name in storage.

The router was able to boot because once it failed booting, it did a final autoboot attempt from default boot device. It looked for the first file in flash and was able to boot from it, so the router came up.

  1. Look at the configuration with show run, and note the config has only one boot statement with boot system flash test.bin.

  2. Look at the show startup-config output interface configuration. Notice that the configuration for the interfaces have no IP addresses and no routing protocol.

  3. First, let’s check the config register with the show version command, looking at the end of the output.

Note: The config register is set to 0x2101, which is a config register used in the old days, booting in to bootstrap mode (a mini-IOS).

Looking at old 2500 series router

Look at this old Cisco 2500 Series Router. It has asynchronous ports on the left to connect to the consoles of multiple devices (as a terminal server), and there are two serial interfaces on the right. This old device would have a bootstrap mode (mini-IOS), but that does not exist on modern routers. The bootstrap mode is irrelevant for this router in Packet Tracer and any modern router.

  1. Change the config register by issuing the conf t and config-register 0x2102 commands. Reload the router to change the config register location. Do not save the changes to the boot location we fixed earlier; we will need to fix them a different way.

Remember that to solve the issues, we are not allowed to make any configuration changes to the device, so simply configuring the interfaces is not an option in this scenario.

  1. Issue a show flash command and note that the flash storage has a file called live-config. This might be a backup configuration we could use. Let’s look at what is inside, using the more flash:live-config command to read the contents of the file. Note that the config has the incorrect boot statement but does have the EIGRP and interface configuration.

  2. To restore the configuration, issue at enable level copy flash running-config. The CLI will prompt you for a filename; we will use the filename live-config that we saw in the flash storage. The destination is the running config. Now we will see the interfaces come up and the routing come up.

  3. Issue a show ip interface brief command to verify that the interfaces and IP addresses are up. Also, issue a show ip protocol to see the EIGRP info. A show run still has the incorrect boot statement, but everything else is there.

When you restore configuration like we did here, interfaces are shut down. So we will need to enable those interfaces.

  1. Turn the interfaces back up by entering the following commands (to bring the interface and EIGRP up):

  1. Verify that we can ping the loopback of routers R1 and R2 with ping 1.1.1.1 and ping 2.2.2.2 at enable mode.

  2. Remove the bad boot statement with the conf t and no boot system flash test.bin commands. Verify that it is gone with a show run. Make sure to update the startup-config by issuing a copy running-config startup-config, and reload the router.

  3. Power-cycle all the devices using the button on the bottom left to verify that everything is fixed. The network will go down, but they should come back up after the reload with our fixes.

Topology rebooted with all the fixes

The fixed topology file is here.

Congrats! Please continue your learning through our community’s many other resources, helping folks get started on their CCNA journey.

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