One More Handy Switching Command - Quick way to check the Root SW

So here is another handy command to find Root SW status locally.

CoreSW#show spanning-tree | inc VLAN|This 

VLAN0001
VLAN0020
             This bridge is the root
VLAN0060
             This bridge is the root
VLAN0160
             This bridge is the root
VLAN0163
             This bridge is the root

The output shows that this SW is the root bridge for all configured VLANs except for vlan 1

Regards,

Deepak Arora

Troubleshooting Layer 1 Cabling Issues - Cisco Catalyst Switches TDR Feature

Cisco TDR (Time Domain Reflectometer)

In Cisco IOS Release 12.1(19)EA1 or later, you can use the Time Domain Reflector (TDR) feature to diagnose and resolve cabling problems. When running TDR, a local device sends a signal through a cable and compares the reflected signal to the initial signal.

TDR is supported only on 10/100/100 copper Ethernet ports. It is not supported on 10/100 ports, 10-Gigabit module ports, or on SFP module ports.

TDR can detect these cabling problems: 

•Open, broken, or cut twisted-pair wires—The wires are not connected to the wires from the remote device.

•Shorted twisted-pair wires—The wires are touching each other or the wires from the remote device. For example, a shorted twisted pair can occur if one wire of the twisted pair is soldered to the other wire.

If one of the twisted-pair wires is open, TDR can find the length at which the wire is open.

Use TDR to diagnose and resolve cabling problems in these situations:

•Replacing a switch

•Setting up a wiring closet

•Troubleshooting a connection between two devices when a link cannot be established or when it is not operating properly 

Example:

core-switch#test cable-diagnostics tdr interface gi0/24
TDR test started on interface Gi0/24
A TDR test can take a few seconds to run on an interface
Use 'show cable-diagnostics tdr' to read the TDR results.


core-switch#show cable-diagnostics tdr interface gigabitEthernet 0/24
TDR test last run on: November 19 14:54:18

Interface Speed Local pair Pair length        Remote pair Pair status
--------     -----   ----------- --------------       -------------- ---------------
Gi0/24    1000M  Pair A     4    +/- 4  meters Pair A        Normal             
                        Pair B     4    +/- 4  meters Pair B        Normal             
                        Pair C     5    +/- 4  meters Pair D        Normal             
                        Pair D     4    +/- 4  meters Pair C        Normal

It means Gi0/24 is running on 1000 Mbps speed, All four pairs have cable length of 4 meters & corresponding remote pair side (for local pair) is working Normally.

The previous command is set to be deprecated sometime in the future and will be replaced by:

" show diagnostic result interface GigabitEthernet 0/24 "


Thanks!

Deepak Arora

The New Cisco ISR G2 Series

http://www.cisco.com/assets/prod/rt/isr/whats-new-isrg2.html

Some more handy "show" commands for CCIE Lab students...hmmm... actually for everyone to know

So here are some quick tips from real world prospective which will definitely save up your time in production networks before you start scratching your head 
:)

1. Here is a quick tip about alias...we all know how to configure that, personally I don't use that at all but some guys prefer it....anyways keep in mind next time you just create an Alias is if you type an alias and type space after it before hitting Enter...it's not gonna work like other commands does...let me make it a bit more clear to understand...lets say for demo I am counting * as a space character and my alias is say DEEPAK for sh version


now if I type Router#DEEPAK* and hit enter...it will not work but if I type Router#DEEPAK and hit enter...it will work just fine...but this space after command does work for all normal commands and doesn't make difference in execution of it like Router#sh version* or Router#sh ver.....both will display same output and will actually work.


2. Few handy show commands for those who are aiming for CCIE R&S lab like me ...basically this helps you see what exactly you wanna see like I love 

"sh ip int br | i up"

"sh ip int br | e unassigned"

"sh ver | i IOS"

and one special switching command: switch#sh ver | i Base


and here is the killer command that I just figured out today after beating my head against the wall to figure out the correct syntax...actually took me quite a few minutes before figuring it out...but finally got it rightly :)

"sh ip int br | e unassigned|down"

Regards,

Deepak Arora

Difference between CBAC & ZBF

http://www.cisco.com/en/US/prod/collateral/vpndevc/ps5708/ps5710/ps1018/prod_white_paper0900aecd806f31f9.pdf