In Cisco devices, the show commands are a way to obtain the information needed from the device in general and specific feature status such as DHCP, Interfaces, OSPF, neighbors etc. in particular.
The show version command provides the bird’s eye view of the device in terms of the IOS version, hardware platform, interface details etc. Being informed about the device is as important as the configuration on it. In the light of this, let’s dissect the show version output of a router and take a deep look on each of its sections. I’m using the Cisco ASR-1006 router running IOS-XE.
The show version is a user-exec mode command that doesn’t require any privileges to run on the router.
Router> show version Cisco IOS Software, IOS-XE Software (PPC_LINUX_IOSD-ADVENTERPRISE-M), Version 15.2(4)S4, RELEASE SOFTWARE (fc1) Technical Support: http://www.cisco.com/techsupport Copyright (c) 1986-2013 by Cisco Systems, Inc. Compiled Sun 01-Sep-13 09:48 by mcpre IOS XE Version: 03.07.04.S Cisco IOS-XE software, Copyright (c) 2005-2013 by cisco Systems, Inc. All rights reserved. Certain components of Cisco IOS-XE software are licensed under the GNU General Public License ("GPL") Version 2.0. The software code licensed under GPL Version 2.0 is free software that comes with ABSOLUTELY NO WARRANTY. You can redistribute and/or modify such GPL code under the terms of GPL Version 2.0. For more details, see the documentation or "License Notice" file accompanying the IOS-XE software, or the applicable URL provided on the flyer accompanying the IOS-XE software. ROM: IOS-XE ROMMON Router uptime is 9 minutes Uptime for this control processor is 12 minutes System returned to ROM by reload System image file is "bootflash:/asr1000rp1-adventerprise.03.07.04.S.152-4.S4.bin" Last reload reason: PowerOn cisco ASR1006 (RP1) processor with 1694412K/6147K bytes of memory. Processor board ID FXS1748Q0U3 5 Gigabit Ethernet interfaces 8 Serial interfaces 8 Channelized E1 ports 32768K bytes of non-volatile configuration memory. 4194304K bytes of physical memory. 917503K bytes of eUSB flash at bootflash:. 39004543K bytes of SATA hard disk at harddisk:. Configuration register is 0x2102
1. IOS Version
Of course, the primary reason we run show version is to know the IOS version running on the device. And it’s shown at the beginning of the command output.
Everything you need to know about IOS version and naming here.
2. License and Copyright Information
Next section tells us what we need to know related to the license and copyright of the software. This section also brought out sensitive information related to cryptographic modules, country specific restrictions on the usage of software etc.
Inside the router motherboard you’ll find a ROM chip which is used to store bootstrap code which will then load the rest of the IOS from Flash memory during booting process. ROM contains a mini-IOS called ROMMON (ROM Monitor) which is helpful to perform router password recovery procedure, download softwares using the Serial connection and upgrade the IOS, if you will. To enter into the ROMMON mode, you have to hit Break while the router is booting. This section of the show version output shows the name of the ROM chip detected.
4. Uptime and System Image file
- Moving further down, the uptime of the router tells how long has the router been up and running, plus the uptime of the control processor of the router.
- What made the system to return to ROM?
- Absolute path of the IOS image file. Required if you want to backup the image via a TFTP server.
- What was the reason for last reload of the router?
5. Hardware configuration
This section is the second most important one, next to IOS version. We’ll get to know
- Processor on the motherboard of the router. And the processor board ID.
- Amount of system memory (RAM).
- List of interfaces on the router. For example, my router has 5 Gigabit Ethernet Interfaces which enables me to route between five different LANs. Plus 8 Serial WAN interfaces allowing me to have up to eight WAN connections, meaning I can reach out and connect eight other routers or networks. “Channelized E1” indicates the type of serial connectivity enabled on those 8 serial ports. These 8 serial ports are the result of the E1 card plugged into the router.
- The size of Non-volatile RAM (NVRAM) which stores the startup configuration of the router.
- The flash storage size that homes the IOS images.
- The hard disk capacity in which root file system is mounted.
6. Configuration Register
A special register called Configuration Register is a 16-bit (2-byte) register whose value affects the behavior of the router. The configuration register value also sets the console baud rate to be used on terminal connections. Two well-known values are,
0x2102 — Ignores the Break during booting, boots into ROMMON if no IOS is found in Flash memory and sets the console baud rate to 9600 bits/sec, which is the default speed on most of the platforms.
0x2120 — Boots into ROMMON and sets the baud rate to 19200 bits/sec.
show version shows the value of the configuration register.