One 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:
Cisco IOS Software, C800 Software (C800-UNIVERSALK9-M), Version 15.4(1)T1, RELEASE SOFTWARE (fc2)
Technical Support: http://www.cisco.com/techsupport
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
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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)
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:
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:
Chassis Serial Number :
Product (FRU) Number : CISCO881-K9
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.” 🙂