from isl to 802.1q

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Dec 30th, 2008
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Hi you all

just to confirm

I have 2 catalyst 6500 conected using a isl trunk

in both I have:

interface GigabitEthernet2/1


switchport trunk encapsulation isl

switchport mode trunk

no cdp enable

In this config I do not need to declare my vlans in both switches. Is that a property of isl protocol?

But if I go with 802.1q, wich is wath I need, I would have to declare all the vlans in both switches, is that correct??


have a nice day

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Jon Marshall Tue, 12/30/2008 - 08:27
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Not sure what you mean by "declare my vlans in both switches".

The automatic update of the vlan database on each switch is done by VTP, assuming you are using VTP Server/Client setup. VTP is not dependant on the trunk encapsulation ie. it will work over ISL or 802.1q.

So it is not a property of ISL it is VTP which will also work with 802.1q.


glen.grant Tue, 12/30/2008 - 08:32
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Basically what you have currently is trunk link using isl as the encapsulation and all vlans are allowed across the trunk because you have not manually pruned off any vlans on the trunk , if you change to dot1q nothing really changes other than the trunk encapsulation which will then be dot1q. Maybe you can explain what you mean by "declare my vlans" in both switches.

languedoc Tue, 12/30/2008 - 13:46
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I thank you very much.

I want to use 802.1q instead of isl because thjose switch will be used in a MSTP enviroment together with hp procurve switches.

I there is vtp server and a client if for a reason the vtp server stop working i will get into trouble.

if VTP is a cisco protocol it will not be usefull with hp procurve switches. So I have to stop vtp, rigth?


viyuan700 Tue, 12/30/2008 - 13:53
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if VTP is a cisco protocol it will not be usefull with hp procurve switches. So I have to stop vtp, rigth?

VTP is cisco protocol but it can send advertisements over ISL/802.1Q.

If you hp procurve switches supports 802.1Q then there is no problem in my opinion.

languedoc Wed, 12/31/2008 - 03:58
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Sorry for my English

I mean adding(configuring) the vlans in all switches.



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