1. Cisco Ios Reload Command
2. Cisco Ios Reload Command Guide
3. Cisco Ios Reboot

Over the years, I have used the reload command for more than upgrading the IOS on a switch or router. The reload command has several parameters that you can pass to it. The ‘reload in’ is one of my most favorite commands, but it is also a very dangerous one. This one command has saved.

Recently, I wanted to upgrade my test router to the latest IOS. I had read about the new Cisco IOS warm upgrade and warm reload features, and I took this opportunity to test them out. By using these features, you can minimize downtime for your end users when you have to upgrade or reboot your router. Here is how I performed a warm upgrade and warm reboot on a Cisco 2811 Router.

What are the warm upgrade and warm reload features?

The warm upgrade feature of the Cisco IOS was offered in Cisco IOS version 12.3(11)T. The warm reload feature of the Cisco IOS was offered in IOS version 12.3(2)T.

Routers are one of the most critical features of your network infrastructure. As network administrators, it is our job to minimize network downtime. Both of these Cisco IOS features — warm upgrade and warm reload — are there to minimize router downtime anytime you do a router upgrade or reboot.

Without further delay, let's see how to use these powerful Cisco IOS features.

How to perform a warm upgrade in the Cisco IOS

I started with a Cisco 2811 Router running IOS 12.4(3g). I wanted to upgrade it to 12.4(15).T5. Within my Cisco IOS license, I downloaded IOS version c2800nm-advipservicesk9-mz.124-15.T5.bin and made it available to download from the TFTP server on my PC.

Next, I used the reload warmfile command, like this:

This command actually has a number of options such as scheduling and creating a comment:

The file that you are upgrading from could be any valid source that the router can access.

Click here to see what the warm reload upgrade file looks like.

To reiterate, the reload warm file

Cisco Ios Reload Command

command allows the router to read and decompress the image while the router continues to process packets. I was able to ping the router the whole time the image was being downloaded and decompressed. The router is only down for the very short time while the IOS image is overwritten with the new image. From my test, that downtime was about 45 seconds. It is amazing to be able to transfer a 45MB file to the router, have it installed, decompressed, and have the router reload, with only 45 seconds of downtime!

Now, what about warm reload?

How do you use warm reload in the Cisco IOS?

The job of the warm reload feature is to allow you to reload your routers without having to read the IOS image from flash. This allows the router to skip the ROMmon phase and copying the IOS image from flash and decompressing it. In other words, with warm reload, the router is able to reboot much faster than ever before. I did some time comparisons, and on my 2811 router, a regular reload took one minute where a warm reload took only 25 seconds.

Using warm reload is simple. You can configure the warm reboot functionality with the warm reboot global command, like this:

This enables the router to reboot a maximum number of 10 times using the warm reboot function and ensures that the router will sit for no more than 10 minutes after an attempted warm reload that doesn't result in a successful boot.

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Next, you must do one clean, cold reload of the router. After that, you can use the reload warm command to quickly reboot your router.You can also use show warm-reboot to find the statistics concerning how many warm reloads have happened and how much space is taken up by warm reload storage. Here is what it looks like:Other related commands are show warm-reboot and debug warm-reboot.A warm reboot looks similar to a normal reboot, but there is no initializing of the memory, no ROMmon initialization, and no decompressing of the IOS image. Again, don't forget to use the reload warm command or else it is just a regular reload.

Less downtime

The warm reload and warm upgrade commands are very useful for any Cisco router admin. I hope that these few simple commands can help keep your routers up and running and available!

For more information on these features, see the Cisco IOS official documentation on the warm upgrade and warm reload features of the Cisco IOS.

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Becoming proficient with the Cisco IOS means learning some essential commands. This quick reference describes 10 commands you'll need to rely on when handling various configuration and troubleshooting tasks.

#1: The '?'

It may seem entirely too obvious that you should know how to type ? to ask for help when using the Cisco IOS. However, the Cisco IOS is completely different from other operating systems when it comes to using the question mark (help key). As the IOS is a command-line operating system with thousands of possible commands and parameters, using the ? can save your day.

You can use the command in many ways. First, use it when you don't know what command to type. For example, type ? at the command line for a list of all possible commands. You can also use ? when you don't know what a command's next parameter should be. For example, you might type show ip ? If the router requires no other parameters for the command, the router will offer <CR> as the only option.

Finally, use ? to see all commands that start with a particular letter. For example, show c? will return a list of commands that start with the letter 'c'.

#2: show running-configuration

The show running-config command shows the router, switch, or firewall's current configuration. The running-configuration is the config that is in the router's memory. You change this config when you make changes to the router. Keep in mind that config is not saved until you do a copy running-configuration startup-configuration. This command can be abbreviated sh run.

SEE: Server deployment/migration checklist (Tech Pro Research)

#3: copy running-configuration startup-configuration

This command will save the configuration that is currently being modified (in RAM), also known as the running-configuration, to the nonvolatile RAM (NVRAM). If the power is lost, the NVRAM will preserve this configuration. In other words, if you edit the router's configuration, don't use this command and reboot the router—those changes will be lost. This command can be abbreviated copy run start. The copy command can also be used to copy the running or startup configuration from the router to a TFTP server in case something happens to the router.

#4: show interface

The show interface command displays the status of the router's interfaces. Among other things, this output provides the following:

• Interface status (up/down)
• Protocol status on the interface
• Utilization
• Errors
• MTU

This command is essential for troubleshooting a router or switch. It can also be used by specifying a certain interface, like sh int g0/0.

#5: show ip interface

Even more popular than show interface are show ip interface and show ip interface brief. The show ip interface command provides tons of useful information about the configuration and status of the IP protocol and its services, on all interfaces. The show ip interface brief command provides a quick status of the interfaces on the router, including their IP address, Layer 2 status, and Layer 3 status.

#6: config terminal, enable, interface, and router

Cisco routers have different modes where only certain things can be shown or certain things can be changed. Being able to move between these modes is critical to successfully configuring the router.

For example, when logging in, you start off at the user mode (where the prompt looks like >). From there, you type enable to move to privileged mode (where the prompt looks like #). In privileged mode, you can show anything but not make changes. Next, type config terminal (or config t) to go to global configuration mode (where the prompt looks like router(config)# ). From here, you can change global parameters. To change a parameter on an interface (like the IP address), go to interface configuration mode with the interface command (where the prompt looks like router(config-if)#). Also from the global configuration mode, you can go into router configuration using the router {protocol} command. To exit from a mode, type exit.

#7: no shutdown

The no shutdown command enables an interface (brings it up). This command must be used in interface configuration mode. It is useful for new interfaces and for troubleshooting. When you're having trouble with an interface, you may want to try a shut and no shut. Of course, to bring the interface down, reverse the command and just say shutdown. This command can be abbreviated no shut.

SEE: Systems downtime expense calculator (Tech Pro Research)

#8: show ip route

The show ip route command is used to show the router's routing table. This is the list of all networks that the router can reach, their metric (the router's preference for them), and how to get there. This command can be abbreviated sh ip ro and can have parameters after it, like sh ip ro ospf for all OSPF routes. To clear the routing table of all routes, you do clear ip route. To clear it of just one routes, issue the command clear ip route x.x.x.x (where x.x.x.x is the network you want to clear).

#9: show version

The show version command gives you the router's configuration register (essentially, the router's firmware settings for booting up), the last time the router was booted, the version of the IOS, the name of the IOS file, the model of the router, and the router's amount of RAM and Flash. This command can be abbreviated sh ver.

#10: debug

The debug command has many options and does not work by itself. It provides detailed debugging output on a certain application, protocol, or service. For example, debug ip routing will tell you every time a route is added to or removed from the router. Debugging can be dangerous as its process takes priority over all others. Be prepared to disable the feature using the no debug command or undebug all command.

Editors note: This article was originally published on TechRepublic July 25, 2006. It was updated on November 30, 2017. The original version is also available as a PDF download.

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