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Can VLAN NO be differnt on differnt Switches?

Posted on 2008-06-19
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Last Modified: 2010-05-19
Deal All,

I would need some help on understanding how the below is working. Its been some time i had to work on VLAN's and i am confused after looking into the below design. Also all the below switches are in a differnt VTP Domain in Server Mode.

There is a L3 switch called SW1 which has has a VLAN100  with routing enabled. The vlan has a ip helper address assigned so that the users can get IP Automatically. Then this SW1 is connected to a Layer 2 switch which is called SW2 via a Access Port. And in the SW1 the access port vlan number stated is VLAN 100. BUt on the other end in the SW 2 the VLAN number stated is VLAN002 as an Access Port and also all the ports on the switch has VLAN002 as the vlan. Firstly how does ths work? Can VLAN Names be differnt on differnt switches? I know that VLAN on differnt VTP Domain does not need to be the same. But i would like to know how the packets really flow?


Also adding to this. This SW2 is conneted to a another L2 switch SW3. The SW2 and SW3 is connected by an access port where SW2 end the access port vlan is VLAN002 but in the SW3 the access port VLAN is nothing which mean it is the default VLAN1. But in he SW3 the default gateway is set to the VLAN100 IP in the SW1.

I know it is quite difficult to understand what i am trying to say but i have put it the most simplest way i can, hope to get some answers from you all.


NOTE: Other than the ports connected to the switches the other ports are set to portfast. in the above i have just mentioned only  1 VLAN100 example, as of now there are many another VLAN between those 3 switches and are names differntly in others 2.

Thanks
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Question by:kamalgopi
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from_exp earned 2000 total points
ID: 21828621
hi!
when you have switches connected with access ports, each switch can have its own vlans, because access vlan means: "all incoming packets treat as if in vlan X"
Note, word "incoming", because outgoing packets are not marked. so unless you connect switches with trunked ports vlan IDs can be different in each switch.

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by:kamalgopi
ID: 21828963
Hi,

Thanks a lot for sharing that info, this was something new for me. Now i totally understand how it works.

Right now i am planning to have 2 more VLANs in the SW3, instead of creating a Trunk and disturbing the whole design(i have just told 3 switches but in the real world we have some 40 to 50 switches) i can just create an another Access Port to the SW2 with the new VLAN i am creating? This should make it work right?

I know creating an Trunk is easier but it would need a lot of changes and surely the local people would not want to change anything, they are very content with what they have now.

Thanks
Hari
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LVL 21

Expert Comment

by:from_exp
ID: 21829289
trunk is much better, than plugging two cables between switches each within its own vlan, because you can avoid creation of potential loop.
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LVL 11

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by:kamalgopi
ID: 21829527
Hi ,

Yeah me also decided on Trunk and just to allow that particular VLAN on it. I would sit down and plan it properly instead of just do a Temp thing. Thanks a lot for your suggestion.

Regards
Hari
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