In this example, I'm connected to the console of a router, when I type enable and then show version,
we can see the version of Cisco iOS running on this router. So here's the show version command Cisco
iOS software that we're running as an 1841 version of software.
It's advanced enterprise software version 15.1(4)M8 release software FC2 what you'll notice
is that a version of software is different to the software in ROM or read only memory. The system bootstrap
a version
here is 12.4 this router has been up for 5 hours and 40 minutes.
This is the version of operating system that the writer booted.
So the system image file is this file which is stored in Flash and that was loaded into memory.
Spaceball shows me more information and I'll be able to see as an example, the amount of RAM in the
router as well as the amount of NV
RAM. Before I look at that, let's use the command show Flash notice
there's the operating system that was loaded into RAM on the router.
So Show Flash is similar to your hard drive.
We have the operating system as well as another file stored in Flash.
This is the size of flash in bytes and this is how much has been used.
Here's another router.
Show Flash here
shows us that a different version of operating system is found in the Flash of this router and other
files are also stored in the Flash of the router.
So this is very similar to a hard drive where multiple files can be stored in flash.
As an example, I could use a command show run pipe
and then redirect the output to Flash
and let's create a file called showruntest.
cfg
and now when I use the command show flash, notice that file is available in Flash, I've just copied
the running-config from RAM onto the flash drive on this router.
You can use the more command to view that file
and what you'll notice is it shows us that this is the current config at a specific time, and that's
because this is a copy of the running-config on the router.
So the running-config of the router is stored in RAM.
So the show running-config or show run command for short shows us the size of the current configuration.
In other words, the live config that's used by the router, the show startup-config or show start
config shows us the saved configuration stored in NVRAM notice the difference.
Show startup shows us output using so many bytes out of so many bytes, whereas the show running-config
shows current config being so many bytes. So just know the output when you use show run, you're going
to see current config.
When you use the command show startup-config or show start
you're going to see so many bytes out of so many bytes.
Now, we could use the command erase startup-config, I noticed we're told that we are going to erase the
NVRAM file system. Do we want to continue?
And I'm going to press enter to confirm that we want to erase the startup-config.
So now when we use the command show startup-config, we are told that there is no startup-config present,
no startup configuration is stored in NVRAM, but the running-config is still available on the
router.
To save the configuration, we would use the command copy running-config, startup-config,
and that copies the configuration from RAM to NVRAM.
So now when we type the command show startup-config,
we see that a config is stored in NVRAM.
That config is not live, so as an example, if I created a loopback interface on this router and
gave it an IP address of something like the following.
Show IP interface brief
shows me that that IP address is available now on the loopback interface on the router.
In other words, the change was immediate, show run
shows us that loopback interface, in other words, it happened immediately and was added to the running
config.
Show startup-config, however, doesn't show us the loopback interface changes are only written to the
startup-config when you use the copy run startup-config command or WR for short.
So now when we look at the startup-config
you'll notice that the loopback interface is configured as part of the startup-config. So the running
config is stored in RAM startup-config is stored in NVRAM.
You can copy the startup-config to NVRAM by using the command copy running-config startup-config.
That would be an exam answer, but for the real world, you could simply use the command WR, you can
also store files in Flash.
So as I demonstrated, you could copy the running-config or startup-config to flash.
Flash can store multiple files as seen on this router
but the primary file that flash is used for is the storing of the operating system, which is loaded
into RAM when the router boots up. Flash is nonvolatile
in other words, when the router reboots, this file is not lost, but it will be removed from RAM when
the router boots up
the operating system is copied from Flash to RAM so that it can be used in real time.
So let's look at the show version
command again.
This shows us information once again about the uptime of the router, the operating system used, how it
was reloaded.
So this was normal reload
and scrolling down, we can see the amount of RAM available on the router now that's in kilobytes.
To get the total RAM on the router you need to add those two together, so 239616
+ 22528.
That gives us the amount of RAM on the router.
So we need to divide by 1024, and that shows us the amount of RAM on this router, it's got 256 mega
ram.
This router, however, is using a different version of operating system, as we've seen and has a
different amount of RAM, so 233472 plus 286
72 gives us that divide by 1024
also gives us 256 mega ram. So you need to add these values together to work out the amount of RAM in
the router.
You'll notice that the NVRAM value is a lot smaller than RAM, only 191 kilobytes of NV
RAM is available, whereas we've got 256 megabytes of RAM available.
This is the size of the compact flash on this router, which is the same on this router.
Notice this router has two FastEthernet interfaces and two serial interfaces, whereas this router
has two FastEthernet interfaces, one serial interface, and one VPN module.
The interfaces on a router can vary, show IP interface brief
on this router shows us the physical interfaces and once again show IP interface brief, on this router
shows us the interfaces on it, which are different to router 1.