Cisco Router With An Identity Crisis

June 23, 2014 — 2 Comments

identity-crisisOne of my favorite interview questions to ask network engineering candidates is “How many different ways can you describe to determine the serial number of a Cisco router?”

Surprisingly, a majority of candidates never get beyond physically inspecting the router to obtain the serial number.  A few give me the obvious answer of using the “show version” command and a rare handful have ever given me more than two commands that might display that information.

Yet, despite the many ways to determine the serial number of a Cisco router and the thousands of Cisco routers that I’ve managed, I finally came across this unsociable router.

Here are the results from a “show version” command on a Cisco C881-series router.  You can actually see the serial number (FTX18138205) is displayed multiple times in this output.  This is the way it should look:


Router#show version
Cisco IOS Software, C800 Software (C800-UNIVERSALK9-M), Version 15.4(1)T1, RELEASE SOFTWARE (fc2)
Technical Support:
Copyright (c) 1986-2014 by Cisco Systems, Inc.
Compiled Wed 12-Feb-14 06:45 by prod_rel_team

ROM: System Bootstrap, Version 15.4(1r)T, RELEASE SOFTWARE (fc1)

Router uptime is 2 minutes
System returned to ROM by reload at 11:38:09 UTC Fri Jun 20 2014
System image file is "flash:c800-universalk9-mz.SPA.154-1.T1.bin"
Last reload type: Normal Reload
Last reload reason: Reload Command

This product contains cryptographic features and is subject to United
States and local country laws governing import, export, transfer and
use. Delivery of Cisco cryptographic products does not imply
third-party authority to import, export, distribute or use encryption.
Importers, exporters, distributors and users are responsible for
compliance with U.S. and local country laws. By using this product you
agree to comply with applicable laws and regulations. If you are unable
to comply with U.S. and local laws, return this product immediately.

A summary of U.S. laws governing Cisco cryptographic products may be found at:

If you require further assistance please contact us by sending email to

Cisco C881-K9 (revision 1.0) with 988236K/60339K bytes of memory.
Processor board ID FTX18138205
5 FastEthernet interfaces
1 Virtual Private Network (VPN) Module
DRAM configuration is 32 bits wide
255K bytes of non-volatile configuration memory.
250880K bytes of ATA System CompactFlash (Read/Write)

License Info:

License UDI:

Device# PID SN
*1 C881-K9 FTX18138205

License Information for ‘c800’
License Level: advipservices Type: Permanent
Next reboot license Level: advipservices

Configuration register is 0x2102


But here you can see our identity-challenged router doesn’t display it’s serial number:


Router#show version
Cisco 881 (MPC8300) processor (revision 1.0) with 236544K/25600K bytes of memory.
Processor board ID

Thinking this could possibly be a bug in the IOS, I tried a couple more commands to see if I coax the router into telling me who it was:


Router#show diag
Chassis Serial Number :
Product (FRU) Number : CISCO881-K9



Router#show inventory
NAME: "881", DESCR: "881 chassis, Hw Serial#: , Hw Revision: 1.0"
PID: CISCO881-K9 , VID: V01 , SN:


As you can plainly see, this router clearly doesn’t know who it is. I could manually set the serial number in the configuration but at this point, I don’t trust this router enough to put it into production. When I need to know what we have deployed in the field, I don’t want a router giving me any more difficulties than they already do.

I think we’ll be sending this one back to be “re-educated.” 🙂

Aaron Melton


2 responses to Cisco Router With An Identity Crisis

  1. Pay very close attention to your router version and its IOS version.

    Cisco’s 881 router had to be redone due to lead concerns. The revamped version of this router is called the “C881”. It runs the c800-universalk9 firmware. This is what you posted in your initial screen shot.

    The original version was called the Cisco881 and ran the c880-universalk9 firmware. This is likely what you are running in your second screenshot as the original Cisco881 includes the “Cisco 881 (MPC8300) processor” line where the new C881 router does not include such a line.

    So why did the router lose its mind? Despite the newer c800-universalk9 firmware for the C881 router being twice as large as the c880-universalk9 for the older Cisco881, I do not believe that the new firmware can run on the older router.

    Therefore, take a look at what you have copied on to the flash, and do a show run | i boot to confirm what firmware the router is trying to use. If you have any copies of C800-universalk9 firmware on the older Cisco881, delete them and any references to them, and replace them with a c880-universalk9 image. As of this moment, TAC recommends version 15.2(4)M6a for the older Cisco881.

    • Excellent observation!

      This is how the router came shipped from Cisco and although I’ve seen licensing issues in the past because of incorrect IOS versions, I’ve never seen a missing serial number. I wanted to spend some time messing with it but I didn’t have an opportunity when I discovered it, so I captured information from the router (that I used to write this blog post) and stuck it back in the box. I believe another Engineer has already RMA’d it but if it comes up again, I’ll look further into the issue. Thanks for the comment!

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