Cisco ISR G2 Router Serial Number

It's funny, I've been working with ISR G2 routers for quite some time now but I recently found out there's another way of checking its serial number. Aside from the serial number indicated on the carton box and beneath the router, there's a pull-out label found at the back of the router. It's right in the middle of the EHWIC0 and the secondary power supply module.

This is a convenient way of checking out the serial number without having to go to CLI or if there's another device rack mounted beneath it. On older ISR router, the serial number sticker is usually found behind the router and is above the FE0/1 port.

Here's a sample of the flip serial number tag on a Cisco 2911 ISR G2 router.

Cisco 3900 ISR G2 Power Supply and Fan Module Swap

I got an escalation from our NOC a couple of weeks back saying one of our core router had an alarm. When I checked the logs, I noticed the CPU temperature was high, one of the the power supply and the fan had failed.

Aug  4 00:25:39.937 UTC: %ENVMON-4-ONE_FAN_LOW_RPM: Warning: Fan 2 is running at low RPM.  Rotation speed is now high for all other fans.  Fan Tray replacement is recommended.

Aug  4 00:28:10.119 UTC: %ENVMON-1-CPU_WARNING_OVERTEMP: Warning: CPU temperature 101C exceeds threshold 95C.  Please resolve system cooling immediately to prevent system damage


3945#show environment
SYSTEM POWER SUPPLY STATUS
==========================
 Internal Power Supply 1 Type: AC
 Internal Power Supply 1 12V Output Status: Normal

 Internal Power Supply 2 Type: Absent 

SYSTEM FAN STATUS
=================
 Fan Rotation Alert: Total 1 Fan Low RPM 
 Fan 1 OK, Maximum speed setting
 Fan 2 Low RPM   
 Fan 3 OK, Maximum speed setting
 Fan 4 OK, Maximum speed setting
 Fan 5 OK, Maximum speed setting

SYSTEM TEMPERATURE STATUS
=========================
 Intake Left temperature: 36 Celsius, Normal
 Intake Right temperature: 29 Celsius, Normal
 Exhaust Right temperature: 44 Celsius, Normal
 Exhaust Left temperature: 49 Celsius, Normal
 CPU temperature: 106 Celsius, Over-Temperature  
 Power Supply Unit 1 temperature: 40 Celsius, Normal

REAL TIME CLOCK BATTERY STATUS
==============================
 Battery OK (checked at power up)

SYSTEM POWER
===============
 Motherboard Components Power consumption = 79.0 W
 Total System Power consumption is: 79.0 W

 Environmental information last updated 00:00:07 ago


I immediately contacted Cisco TAC and asked for an RMA.

The power supply (PWR-3900-AC) has screws on the sides which helps in pulling out from the router's chassis.

These are front and back view of the fan module/assembly (3900-FANASSY). The RMA comes with a new faceplate.

According to Cisco, these modules are hot-swappable so you don't need to turn off the chassis. You also got at least two minutes to do the swap in order to avoid further CPU overheating. When I removed the router's faceplate, I've observed that all five fans weren't rotating and blown air was warm. This issue has been going for at least 3 days before I swapped the new modules. Good thing nothing melted inside :)

When you removed the fan assembly, you would see two power supplies.

Aug  7 13:59:32.305 UTC: %ENVMON-2-FAN_TRAY_MISSING: Critical Warning: Fan tray was removed.  Please re-insert fan tray to prevent system from overheating.
Aug  7 14:00:32.380 UTC: %ENVMON-1-POWER_WARNING: : Internal Power Supply Unit 2  AC or DC input source has been removed.
Aug  7 14:01:02.416 UTC: %ENVMON-5-POWER_NOTICE: : Internal Power Supply Unit 2  12V is UP %ENVMON-5-POWER_NOTICE: : Internal Power Supply Unit 2  12V is UP
Aug  7 14:02:32.683 UTC: %ENVMON-6-CPU_TEMP_OK: CPU temperature normal
Aug  7 14:02:32.683 UTC: %ENVMON-6-FAN_TRAY_OK: Fan tray is detected.


3945#show inventory

<OUTPUT TRUNCATED>

NAME: "C3900 AC Power Supply 1", DESCR: "C3900 AC Power Supply 1"
PID: PWR-3900-AC       , VID: V03 , SN: QCS1726abcde

NAME: "C3900 AC Power Supply 2", DESCR: "C3900 AC Power Supply 2"
PID: PWR-3900-AC       , VID: V04 , SN: QCS173abcde

3945#show environment
SYSTEM POWER SUPPLY STATUS
==========================
 Internal Power Supply 1 Type: AC
 Internal Power Supply 1 12V Output Status: Normal

 Internal Power Supply 2 Type: AC
 Internal Power Supply 2 12V Output Status: Normal

SYSTEM FAN STATUS
=================
 Fan 1 OK, Low speed setting
 Fan 2 OK, Low speed setting
 Fan 3 OK, Low speed setting
 Fan 4 OK, Low speed setting
 Fan 5 OK, Low speed setting

SYSTEM TEMPERATURE STATUS
=========================
 Intake Left temperature: 20 Celsius, Normal
 Intake Right temperature: 19 Celsius, Normal
 Exhaust Right temperature: 20 Celsius, Normal
 Exhaust Left temperature: 22 Celsius, Normal
 CPU temperature: 44 Celsius, Normal
 Power Supply Unit 1 temperature: 21 Celsius, Normal
 Power Supply Unit 2 temperature: 24 Celsius, Normal

REAL TIME CLOCK BATTERY STATUS
==============================
 Battery OK (checked at power up)

SYSTEM POWER
===============
 Motherboard Components Power consumption = 123.6 W
 Total System Power consumption is: 123.6 W

 Environmental information last updated 00:00:10 ago