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Differences between Theory & Practicability

Posted by kashif amir , 25 November 2011 · 3,017 views

Hi Friends !

It has been a while now that I shared something on this forum so now it is the right time to do it.

When you achieve your CCNA, go through a series of interviews and join your new job, Surprisingly what you see in production is a total different perspective of what you see when you prepared for your certification (even if you have some real equipment experience).

I would like to mention some of the variations that may help (which I learnt the hard way).

First of all most enterprise class networks use CISCO 3750 PoE enable switches. The glitch here is that they support stacking ( a methodology where upto nine different switches are connected through 32Gbps stacking cables at the back, so that they behave as a single logical switch and the switchports on different member switches may be referenced as x/0/y where x is the member switch number and y is the swithcport number on individual switch). In the context of stacking, all the switches are one single unit, accessible through single management IP address.

The trouble shooting in the case of hardware problem is a little different than the normal trouble shooting and replacement. Because in a normal switch hardware failure requires the deployment of an identical switch with the configuration loaded through TFTP (most of the cases your Network Management System backs this config on a regular basis). However in the case of a stack member going faulty you don't need to load the config but to make it the same member as of the failed one and connect the stacking cables exactly the same way as were connected to the failed switch.

There are a couple of global config commands for this setup mentioned below:

3750-Stk(config)#switch 1 renumber a

3750-Stk(config)#switch 1 priority b

where "a" is the switch member number of failed switch and "b" is the switch member priority of failed switch.

As soon as this is done (rember to reboot the switch after this because these changes will take effect after first reload). As all the switches members share the same config so the new switch needs to be connected first as of old switches (for all copper,fiber and stacking cables) and then powered up. The stack will again be formed with this new switch and the devices connected to this will be able to get to the network.

To test the switch functioality issue to the show switch command from user / priviledged exec modes and you will see output like this:

3750-Stk>show switch
Switch#  Role      Mac Address     Priority     State
*1       Master     0016.4748.dc80     15         Ready
2       Slave      0016.9d59.db00     14         Ready
The master is indicated with a * and is the one having highest priority and is controlling the stack operations. If the master fails the next higher priority switch will assume the role of master.

I 'll be posting more for this topic and related issues but your feedback is really important.


Kashif Amir

December 2019

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