creating Vlans at Core layer switches ?

Unanswered Question
Nov 1st, 2007

Is there a need to create vlans at core layer switches ? If yes what are the pros and cons for this practice ?

Actually i have seen some networks doing that!

I have this problem too.
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Jon Marshall Thu, 11/01/2007 - 04:56


Not sure what you mean by this. Do you mean create vlans at layer 2 or create Layer 3 interfaces in the core ?

Could you clarify.


a.cruea1980 Thu, 11/01/2007 - 06:58

If you're asking what I think you're asking. . .

Your core switches have supervisors w/ MSFC in them, so they can do routing and switching. Why wouldn't you create vlans on them? Why make the traffic go all the way to your border router to route between VLANs?

Not to mention, VLANs keep traffic segregated.

Ultimately, though, we'll need more info into the topology you're inquiring about. Equipment, stuff like that.

mba7eth_ccie Mon, 11/05/2007 - 02:39

Well this is the topology that i'm working on.

we have implemented the 3 layer approach.

1. At access layer: Switches are all L2 (for sure :) )

2. At distribution layer: All switches are L3 are routes for incoming data.

3. At core we have 2 6500 switches. One is configured as L3 and all vlans are created in it. Second is just as regular L2 device.

and ofcourse there are some switch blocks for server farms and the likes.

My issue is

1. why don't we create vlans at distribution layer switches.

2. Why one core switch is acting as L2 and other is acting as L3. What will happen in case of failure to the one acting as L3.

Ps: the second issue just came up in my mind.


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