show version – System Details and Uptime
Purpose of show version Command
Definition: show version is a vital diagnostic and inventory command for Cisco routers, switches, firewalls, and other devices. It displays comprehensive details about the device's hardware, software, uptime, reload reason, licensing, and more.
- Hardware and software inventory
- Verify device uptime and last reload reason
- Pre-upgrade checks (IOS version, RAM/Flash)
- Troubleshoot restarts or performance issues
Key Information Displayed by show version
| Section | Example Output | What It Means / Use |
|---|---|---|
| IOS Version & Image | Cisco IOS Software, C3750E Software (C3750E-UNIVERSALK9-M), Version 15.2(4)E7 |
Identifies the software version and image loaded; required for feature checks and upgrades. |
| Device Model | cisco WS-C3750E-48PD (PowerPC405) |
Exact hardware model/platform (needed for support and inventory). |
| System Uptime & Reload Reason | uptime is 34 weeks, 2 days, 5 hours |
How long since last reboot and what caused it (crash, power loss, reload command, etc.). |
| Processor & Memory | CPU at 600MHz, 512MB RAM, 128MB Flash |
Shows available resources; critical for upgrades or feature enablement. |
| Configuration Register | Configuration register is 0x2102 |
Controls boot process, console speed, recovery features. 0x2102 is normal, 0x2142 ignores startup-config (used in recovery). |
| Interface Summary | 48 FastEthernet/IEEE 802.3 interface(s) |
Number and type of interfaces detected (verifies hardware presence). |
| License/Feature Info | License Level: ipservices |
Active feature set or licenses, impacts advanced feature availability. |
| Boot Loader & ROMMON | ROM: Bootstrap program is C3750E boot loader |
Boot process details; helps in troubleshooting or password recovery. |
| Processor Board ID | Processor board ID FOC1532X06P |
Device’s unique serial number (asset tracking, Cisco TAC). |
Configuration Register Settings
- 0x2102: Default – boot from startup-config in NVRAM, normal operation.
- 0x2142: Ignore startup-config (used for password recovery).
Role: Controls device boot sequence, console speed, and recovery options.
Interpreting Reload Reasons
The show version output will include a line indicating the cause of the last reload:
- System returned to ROM by power-on: Device rebooted due to power cycle or power failure.
- System returned to ROM by reload command: Administrator manually reloaded device.
- System returned to ROM by software crash: Device experienced a crash, check logs for details.
Practical Use Cases for show version
- Pre-upgrade Check: Confirm IOS version, RAM, Flash, and model before updating software.
- Hardware Inventory: Gather serial numbers and models for asset management or support contracts.
- Troubleshoot Device Reboots: Analyze uptime and reload reason for instability or power issues.
- License Validation: Ensure correct features are active for advanced configurations.
- Password Recovery: Check the configuration register value before and after recovery.
Differences Across Platforms
| Device Type | Unique Details in Output |
|---|---|
| Router | Serial/WAN interfaces, configuration register, processor details |
| Switch | Ethernet/GigabitEthernet interface summary, switch model/family info |
| Firewall (ASA) | Security context, VPN support, firewall features |
Sample Output and Explanation
Switch# show version Cisco IOS Software, C2960S Software (C2960S-UNIVERSALK9-M), Version 15.0(2)SE11 Compiled Wed 22-Apr-20 10:34 by prod_rel_team ROM: Bootstrap program is C2960S boot loader Switch uptime is 3 weeks, 1 day, 4 hours, 22 minutes System returned to ROM by power-on Processor board ID FOC1747W0K1 Last reload type: Normal Reload Last reload reason: Reload command System image file is "flash:c2960x-universalk9-mz.152-4.E6.bin" Configuration register is 0x2102
- IOS Version: 15.0(2)SE11
- Model: Cisco C2960S
- Uptime: 3 weeks, 1 day, 4 hours, 22 minutes
- Reload Reason: Power-on (unplanned reboot, possible power issue)
- Config Register: 0x2102 (normal operation)
Summary Table – Key Fields in show version Output
| Field | Description / Use |
|---|---|
| IOS Version | Software version running; required for upgrades and feature planning. |
| System Image File | Name of the loaded IOS image in flash memory. |
| Device Model | Exact hardware model number (asset management, support contracts). |
| Processor Board ID | Device serial number, uniquely identifies the device. |
| System Uptime | Time since last reboot—helps identify recent outages or instability. |
| Last Reload Reason | Why the device rebooted (manual, crash, power loss). |
| Configuration Register | Boot/recovery behavior; critical for password recovery or boot troubleshooting. |
| Memory (RAM/Flash) | Available resources for upgrades and features. |
| Interface Summary | Type/number of interfaces; confirms expected hardware is present. |
| License/Feature Level | Indicates advanced feature or license level active. |
| Boot Loader/ROMMON | Shows device's bootstrap/ROMMON version for troubleshooting/recovery. |
Exam Tips and Key Points
- Always check uptime and last reload reason to spot unplanned outages.
- Memorize the meaning of key config register values (0x2102 = normal, 0x2142 = recovery).
- Know where to find RAM/Flash details before IOS upgrades.
- Understand platform-specific differences in output (routers vs. switches).
- Record serial/model numbers for TAC cases or support renewals.
Sample Troubleshooting Scenario: Diagnosing a Reboot
Scenario: John is asked to find out why a switch in the server room rebooted unexpectedly overnight, causing an outage.
- He enters:
show version -
He sees:
Switch uptime is 4 hours, 27 minutes
System returned to ROM by power-on (Power failure)
System image file is "flash:c2960x-universalk9-mz.152-4.E6.bin"
Configuration register is 0x2102 -
Diagnosis:
- Device rebooted due to power failure (not a manual reload or crash).
- Uptime confirms the reload happened recently and unexpectedly.
- Device is running the expected IOS image and config register is normal (0x2102).
- If config register was 0x2142: The device would ignore the startup configuration at next boot (commonly used for password recovery).