Configuring Vlan

Unanswered Question
Dec 5th, 2007

Hi all

Is there any situation i would configure a layer 2 Vlan at the distribution layer. I am using layer 3 sw at the distribution layer. If yes , may i know the reason for doing that.

What i usually do is to configure layer 2 vlan at teh access switches and assign workstation to the vlan.

Thanks in advance


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Martin Schoenbacher Wed, 12/05/2007 - 01:08

i think you doing it right. the only reason that comes in my mind for using layer 2 vlan at the distribution layer is if you need one vlan spread across the distribution layer for 2 different sites ...

Jon Marshall Wed, 12/05/2007 - 01:41


In a single bulding you may have a collapsed core/distribution layer contained on a pair of 4500/6500. On each floor you would have access-layer switches for the users which could be connected back to the core/distro switches by L2 or L3 links.

If you have this setup you may have also have servers that you need to connect. The best thing to do would be to have the servers on separate switches which also connect back to the core/distro but due to cost/power/space etc. issues you may just connect the servers directly into the core/distro switches. If you wanted to run HSRP for the server vlans you would then extend a layer 2 vlan across the switches.



caijunjie Wed, 12/05/2007 - 02:08

Hi Jon

Regarding the part to run HSRP for the server vlan., I would need to extend layer 2 vlan accross the switch. May i know what does that mean.

Sorry, I am not very good in understanding that :)


Jon Marshall Wed, 12/05/2007 - 02:13


No need to apologise. What i meant was usually servers are connected to both switches for resiliency. One of the NIC cards is active and the other is in standby, (although you can run them both active but i have never done this), and so you have to have a Layer 2 vlan that exists on both core/distro switches because the 2 server NIC's will need to be in the same vlan.

So your core/distro switches will need to be interconnected with a layer 2 link, usually a trunk.

Hope i've explained it well enough


caijunjie Wed, 12/05/2007 - 02:34

Hi Jon

Thanks for your fast reply. Am i right to mean the following:

If i am connecting workstation to access switches, I would be defining the layer 2 Vlan at the access layer.

If I am connecting servers to the dist sw. I would define the Vlan at the dist layer and at the dist sw, I would convert the port to access port before assigning the port to the Vlan as it is a Layer 3 sw. ?

Please help to advice . THanks

Jon Marshall Wed, 12/05/2007 - 02:39


"If i am connecting workstation to access switches, I would be defining the layer 2 Vlan at the access layer"

It depends on where the L3 interfaces for those vlans are ie. if the inter-vlan routing for the access-layer vlans is done on the distro switches then that means your access-layer switches are connected to the distro switches via L2 links. If so normally you would create the L2 vlan and the L3 interface on the distro switches with the distro switches being VTP servers and the access-layer switches being VTP clients.

If the layer 3 interfaces for the access-layer vlans are on the access-layer switches then yes you would create the L2 vlans on the access-layer switches.

Yes in answer to your second question. You would make the server ports switchports, and define the L2 vlan and the corresponding L3 vlan interfaces on the distro switches.



caijunjie Wed, 12/05/2007 - 20:32

Hi Jon

That a great explaination. THanks, I get what you mean.



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