The importance of skinning cats

Once again the VLAN topic comes to the forefront but immediately I know this will apply to all aspects of the blueprint. The old adage goes something like “There are many ways to skin a cat”.

Lets take the example of creating a VLANs. How many ways can you do it? Well I know of three. I will give an example of each below to show my point.

First Method – VLAN Database

S1#vlan database
% Warning: It is recommended to configure VLAN from config mode,
 as VLAN database mode is being deprecated. Please consult user
 documentation for configuring VTP/VLAN in config mode.
S1(vlan)#vlan 100 name CCIE-vlan100
VLAN 100 added:
 Name: CCIE-vlan100

Note here that we have added a VLAN into the VLAN Database. Remember that you can only have VLANs that are in the standard range which consists of 1-1004. Note also that this method is being deprecated but at time of writing still relevant.

Second Method – Global Configuration

S1(config)#vlan 150
S1(config-vlan)#name CCIE-vlan150

This method is quite easy in comparison. This method is what has replaced directly interacting with vlan.dat via the VLAN database. This is the method that most students are taught when getting their CCNA studies under their belt.

Third Method – Interface creation

S1(config)#int fa0/10
S1(config-if)#switchport access vlan 200
% Access VLAN does not exist. Creating vlan 200

Note here that we have created a VLAN inadvertently by placing an interface into a VLAN which has not been defined. This creates the VLAN in the database. This only applies to standard range VLANs and does not work on all devices.

If you have read my previous article discussing the difference between standard and extended range VLANs you will have more clarity in regards to the following error.

S1(config-if)#switchport access vlan 3500
% Access VLAN does not exist. Creating vlan 3500
00:08:28: %PM-2-VLAN_ADD: Failed to add VLAN 3500 - VTP error.

This error will rear its head due to the fact that the switch cannot write an extended VLAN to the vlan.dat database. The VTP mode which allows extended VLANs to be utilized and written to the running config is transparent mode. VTPv3 does alleviate issues posed here but at this current time is outside the bounds and scope of the CCIE blueprint.

This entry was designed not as a guide to skinning our feline kitties. It’s purpose is to understand that a task may require a different way of execution. I know for a fact restrictions on the CCIE exam make some simple tasks a little trickier. It even takes trickier tasks to the extreme.

By understanding different methods such as those listed above you may avoid some obstacles. If a task stated

  • VLANs 500,1000,2000 must be created. VLAN information must be added to the running configuration concurrently.

You would have to weigh up what method and mode best suits the requirements of the question.

Fundamental understanding of technologies and their applications are important. Playing at the CLI also will reveal what the cause and effect of each word you type. The CCIE awaits me and I best get back to study.

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