Cisco Catalyst 3850 Switch Preparation¶
Complete procedure for preparing Cisco Catalyst 3850 series switches for rental deployment, including physical inspection, password recovery, factory reset, and firmware installation.
Overview¶
This guide covers recovering locked switches, sanitizing flash memory, and loading clean firmware for rental deployment. The Catalyst 3850 is an enterprise-class stackable switch commonly used in data center and campus environments.
Prerequisites¶
| Item | Details |
|---|---|
| Console Cable | RJ-45 to USB/Serial console cable |
| Terminal Software | PuTTY, TeraTerm, or similar (9600 baud, 8-N-1) |
| USB Drive | FAT32 formatted with verified rental .bin firmware |
| Physical Access | Access to Mode button on switch front panel |
Part 1: Physical Inspection¶
Port Integrity¶
| Component | Check |
|---|---|
| RJ45 Ports | Use flashlight to check for bent pins |
| SFP/SFP+ Uplinks | Ensure no debris in optical cages |
| Mode Button | Verify tactile click (essential for reset) |
Stacking Ports (Rear)¶
| Check | Action |
|---|---|
| StackWise Connectors | Remove blind covers and inspect - pins bend easily |
| Blanking Plates | If client didn't order stacking cables, reinstall blanks |
| Stacking Cables | If present, verify secure connection |
Fragile Connectors
StackWise connector pins are fragile. Handle with care and always use blanking plates when not in use.
External Condition¶
| Check | Action |
|---|---|
| Rack Ears | Verify not bent or broken |
| Ventilation | Ensure all vents are clear |
| Labels | Serial number legible |
Part 2: Password Recovery (ROMMON Method)¶
Use this procedure when the switch is password locked.
Enter ROMMON Mode¶
| Step | Action |
|---|---|
| 1 | Power OFF the switch |
| 2 | Press and hold the Mode button |
| 3 | While holding Mode, power ON the switch |
| 4 | Continue holding for ~15 seconds |
| 5 | Release when System LED turns solid amber |
| 6 | switch: prompt appears (ROMMON mode) |
LED Indicator
The SYST LED will blink during boot, then turn solid amber when ROMMON is ready.
Boot from USB (Bypass Locked OS)¶
! Verify USB is detected
switch: dir usbflash0:
! Set boot variable to USB image
switch: set BOOT usbflash0:cat3k_caa-universalk9.16.12.04.SPA.bin
! Boot the switch
switch: boot
Boot Variable
This boots using the USB image, bypassing the locked internal flash.
Part 3: Factory Reset & Data Sanitization¶
Execute Factory Reset¶
Once booted from USB:
! Wait for prompt
Press return to get started
! Enter privileged mode
Switch> enable
! Factory reset (NIST Standard wipe)
Switch# factory-reset all
! Confirm twice when prompted
The switch will reboot and perform a complete system wipe.
Initial Configuration Dialogue¶
After reboot:
| Prompt | Response |
|---|---|
| "Initial Configuration Dialogue" | Answer no |
| "Terminate Autoinstall" | Answer yes |
Part 4: Flash Formatting & Image Installation¶
Format Internal Flash¶
! Enter privileged mode
Switch> enable
! Format flash (deletes EVERYTHING)
Switch# format flash:
! Confirm twice when prompted
Point of No Return
Format deletes all data from internal flash. Ensure USB is still inserted before proceeding.
Copy Image to Flash¶
! Copy from USB to internal flash
Switch# copy usbflash0:cat3k_caa-universalk9.16.12.04.SPA.bin flash:
! Press Enter to accept default destination filename
! Verify copy was successful
Switch# dir flash:
Verification
Compare file sizes - the flash copy should match the USB source exactly.
Set Boot Variable¶
! Enter global configuration
Switch# configure terminal
! Set permanent boot image
Switch(config)# boot system flash:cat3k_caa-universalk9.16.12.04.SPA.bin
! Exit configuration
Switch(config)# exit
! Save configuration
Switch# write memory
! Verify boot variable
Switch# show boot
Final Reload¶
! Reload to verify boot from internal flash
Switch# reload
! Confirm when prompted
Part 5: Post-Reset Verification¶
Basic Checks¶
! Verify IOS version
Switch# show version
! Verify boot configuration
Switch# show boot
! Verify flash contents
Switch# dir flash:
! Check switch status
Switch# show switch
Stack Configuration (If Applicable)¶
! View stack members
Switch# show switch
! View stack ports
Switch# show switch stack-ports
! Set switch priority (for master election)
Switch# switch 1 priority 15
Command Reference¶
ROMMON Commands¶
| Command | Description |
|---|---|
dir usbflash0: |
List USB contents |
set BOOT usbflash0:<file> |
Set boot image |
boot |
Boot the switch |
flash_init |
Initialize flash |
set |
Show environment variables |
IOS Commands¶
| Command | Description |
|---|---|
factory-reset all |
Complete factory reset |
format flash: |
Format internal flash |
copy usbflash0: flash: |
Copy files from USB |
boot system flash:<file> |
Set boot image |
write memory or wr |
Save configuration |
show version |
Display IOS and hardware info |
show boot |
Display boot configuration |
LED Reference¶
| LED | State | Meaning |
|---|---|---|
| SYST | Off | No power |
| SYST | Green | Operating normally |
| SYST | Amber | System error/POST failure |
| SYST | Blinking Green | Booting |
| SYST | Solid Amber | ROMMON mode |
| STAT | Green | Ports operational |
| ACTV | Green | Switch is stack master |
Troubleshooting¶
Cannot Enter ROMMON Mode¶
- Hold Mode button before applying power
- Hold for at least 15 seconds
- Verify Mode button has tactile click
- Try different console cable/terminal settings
USB Not Detected¶
- Format USB as FAT32 (not NTFS or exFAT)
- Try a different USB port
- Verify .bin filename has no spaces
- Try a smaller capacity USB drive (<32GB)
Boot Fails After Reset¶
- Verify boot variable:
show boot - Check file exists:
dir flash: - Re-copy image if checksum fails
- Try booting from USB again
Stack Member Issues¶
! Check stack status
Switch# show switch
! If member shows "Mismatch"
! Boot from USB with matching IOS version
Firmware Recommendations¶
| Series | Recommended Train | Notes |
|---|---|---|
| 3850 | 16.12.x | Stable, long-term support |
| 3850 | 17.x | Latest features |
Firmware Consistency
All stack members must run the same IOS version. Version mismatch causes stack instability.
Process Verification Checklist¶
| Task | Verified | Date |
|---|---|---|
| Physical inspection (ports, Mode button) | ☐ | |
| ROMMON entry successful | ☐ | |
| Boot from USB verified | ☐ | |
factory-reset all executed |
☐ | |
| Flash formatted | ☐ | |
| Image copied to flash | ☐ | |
| Boot system variable set | ☐ | |
| Configuration saved | ☐ | |
| Reload and boot verified | ☐ | |
| Stack operation verified (if applicable) | ☐ |