Cisco CCNA And CCNP Certification Exam Training:

Troubleshooting A Cisco Router With show version and show cdp neighbor

When you were a CCNA candidate, you mainly knew show version as the command that told you what a router's configuration register was.  Obviously, there's a lot more information than that!  Here's show version on one of my switches:

SW1#show version
Cisco Internetwork Operating System Software
IOS (tm) C2950 Software (C2950-I6Q4L2-M), Version 12.1(19)EA1c, RELEASE SOFTWARE
 (fc2)
Copyright (c) 1986-2004 by cisco Systems, Inc.
Compiled Mon 02-Feb-04 23:29 by yenanh
Image text-base: 0x80010000, data-base: 0x8058A000

ROM: Bootstrap program is C2950 boot loader

SW1 uptime is 11 hours, 42 minutes
System returned to ROM by power-on
System image file is "flash:/c2950-i6q4l2-mz.121-19.EA1c.bin"

cisco WS-C2950-12 (RC32300) processor (revision P0) with 20808K bytes of memory.
Processor board ID FOC0814X3G9
Last reset from system-reset
Running Standard Image
12 FastEthernet/IEEE 802.3 interface(s)

32K bytes of flash-simulated non-volatile configuration memory.
Base ethernet MAC Address: 00:0F:90:E1:C2:C0
Motherboard assembly number: 73-5782-13
Power supply part number: 34-0965-01
Motherboard serial number: FOC08150PHU
Power supply serial number: DAB08145W2B
Model revision number: P0
Motherboard revision number: A0
Model number: WS-C2950-12
System serial number: FOC0814X3G9
Configuration register is 0xF

A lot of good stuff here!  Highlighted from the top down:

• The IOS version
• The device uptime (really good for settling "hey, did anyone restart this switch today?" arguments)
• Image filename
• Amount and type of memory
• Standard or Enhanced Image
• Motherboard and power supply serial numbers
• MAC addresses
• Model number
• ... and the configuration register setting!

Another handy and often-overlooked switch troubleshooting tool is show cdp neighbor detail. You know what the basic output of show cdp neighbor looks like:

show cdp neighbor details gives you a great deal more information. Let's look at the output of this command for the neighbor SW2 only:

SW1#show cdp neighbor detail
-------------------------
Device ID: SW2
Entry address(es):
Platform: cisco WS-C2950-12,  Capabilities: Switch IGMP
Interface: FastEthernet0/12,  Port ID (outgoing port): FastEthernet0/12
Holdtime : 126 sec

Version :
Cisco Internetwork Operating System Software
IOS (tm) C2950 Software (C2950-I6Q4L2-M), Version 12.1(19)EA1c, RELEASE SOFTWARE
 (fc2)
Copyright (c) 1986-2004 by cisco Systems, Inc.
Compiled Mon 02-Feb-04 23:29 by yenanh

advertisement version: 2
Protocol Hello:  OUI=0x00000C, Protocol ID=0x0112; payload len=27, value=0000000
0FFFFFFFF010221FF000000000000000F90E22540FF0000
VTP Management Domain: ''
Native VLAN: 1
Duplex: full
Management address(es):

Again, some great troubleshooting information here. Highlighted from the top down:

• The neighbor's hardware platform and capabilities
• The ports on the remote and local devices that are directly connected
• The neighbor's IOS version
• The CDP version ("advertisement version")
• The neighbor's native VLAN

Run these command regularly in your home Cisco lab and know where to find every piece of information listed here - you just never know when you might need to do that for real!

To your success,

Chris Bryant

CCIE #12933

chris@thebryantadvantage.com