Take advantage of Cisco's show version command

As its name suggests, the most common use of the <i>show version</i> command is to determine which version of the Cisco IOS a device is running. However, this command does much more than that—it actually offers several different uses. Let David Davis introduce you to the many uses of Cisco's <i>show version</i> command, and see how its output varies according to which device you're using.

Any network administrators who work with Cisco devices are more than likely familiar with the show version command. The most common use of this command is to determine which version of the Cisco IOS a device is running. However, the show version command does much more than that—it actually offers several different uses.

In my opinion, show version is an underrated and underappreciated command. Its name just doesn't adequately explain all of its uses.

This week, I want to take an in-depth look at the many uses of the show version command, offer examples of the command's output on a variety of Cisco devices, and discuss what information you can gather from that output.

Learn the many uses of the show version command

As I mentioned, the show version command does much more than just display the version of the operating system. Here's a laundry list of other statistics that this powerful command can display:

  • The version of the IOS operating system
  • The version of the ROM bootstrap
  • The version of the boot loader
  • How someone last powered on the device (In addition to powering on in the usual manner, you can also power on a device with a system reset (i.e., warm reboot) or by a system panic.)
  • The time and date the system last started
  • The "uptime" for the system (i.e., how much time has passed since the last power-on)
  • The image file that the device last started (i.e., the actual path to the IOS software)
  • How much RAM the device has
  • The processor board ID, which you can use to determine the version of the device's motherboard
  • The number and type of each interface on the device (e.g., Qty 2 Ethernet, Qty 6 Serial, etc.)
  • The number of terminal lines on the router if a router has asynchronous serial lines attached
  • The amount of nonvolatile RAM (NVRAM), used to hold the SAVED version of the configuration file, also known as the startup-configuration
  • The amount and type of Flash on the device (except on a switch), used to hold the operating system when it isn't in use (Think of it as the equivalent to a hard drive on a PC.)
  • The configuration register on the device, which is a hexadecimal number used to tell the device what to do when it boots. (Typically, this only changes when you need to bypass the configuration file because of a lost password, but you can also change it for other special cases.)
  • The hostname of the device

In addition, the show version command will display specific information on switches:

  • The number of Ethernet switching interfaces
  • The serial numbers of the device and its power supplies
  • The MAC address of the switch
  • The revision number of the motherboard
  • The model number of the switch
  • Whether you've enabled password recovery

On some switches, you can even use this command to return the power supply part number and the motherboard part number. In addition, you can determine whether the switch has the standard or enterprise version of the IOS. (These two IOS types are specific to switches.)

On PIX firewalls, you can use the show versioncommand to display other specific information:

  • The MAC addresses for the interfaces
  • Which licenses you've enabled for which features (such as failover, 3DES encryption, or number of hosts)
  • The activation key for those licenses
  • The last time someone modified the configuration file

Working with the show version command's output

Now that we've covered the various uses of the show version command, let's look at some examples of working with its output. We'll look at sample output from two routers, two switches, and a firewall.

Using the show version command on routers
Listing A shows sample output of the show version command on a Cisco 3845 router, and Listing B shows sample output of this command on a Cisco 2511 router. From this output, we can tell that these routers have different types of Flash memory. The 3845 router, the newer one, has 64 MB of ATA System Compact Flash, as shown in this line:

62720K bytes of ATA System Compact Flash (Read/Write)

On the 2511 router, the older one, we can see that it has only 16 MB of onboard read-only flash, as shown in this line:

16384K bytes of processor board System flash (Read ONLY)

Using the show version command on switches
Listing C shows sample output of the show version command on a Cisco 2950 switch, and Listing D shows sample output of the show version command on a Cisco 3750 switch. On the Cisco 3750 switch, the output shows the amount of RAM on the switch, but you need to add the two numbers shown in this line:

cisco WS-C3750G-48TS (PowerPC405)
processor (revision C0) with 
118784K/12280K bytes of memory.

If you add 118784 K and 12280 K, you get 131,064 K—the equivalent of 128 MB.

In addition, on the Cisco 3750 switch, you can use the show version command to display the device's serial number remotely, as shown below. This offers a big benefit when it comes to locating switches for lease replacement or renewing Cisco maintenance contracts on devices by serial number.

System serial number            : FOC0936U2S8

Using the show version command on firewalls
Listing E offers an example of this command's output on a PIX 501 firewall. The output is very different from the routers and the switches. For example, you can see the list of licenses that this firewall has enabled and disabled, as shown below:

Licensed Features:
Failover:              Disabled
VPN-DES:               Enabled
VPN-3DES:              Enabled
Maximum Interfaces:    2
Cut-through Proxy:     Enabled
Guards:                Enabled
URL-filtering:         Enabled
Inside Hosts:          10
Throughput:            Limited
IKE peers:             5

In addition, this output tells us that there's limited throughput on this firewall and that there can only be 10 hosts on the inside of the interface.

These are just some examples of the many uses of the show version command. It's important to remember that this command's output varies from platform to platform. So, the next time someone asks you what the show version command does, you can demonstrate how this command does a lot more than what its name suggests.

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David Davis has worked in the IT industry for 12 years and holds several certifications, including CCIE, MCSE+I, CISSP, CCNA, CCDA, and CCNP. He currently manages a group of systems/network administrators for a privately owned retail company and performs networking/systems consulting on a part-time basis.

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