Vlan overlap in OSI explaination?

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Apr 9th, 2010
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Hi Guys,

Currently i have a vlan overlap issue here. Does anyone can explain this issue in terms of OSI layers? We know just overlappy but how does it cause issue in layer to layer level?

Thank you

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Federico Coto F... Fri, 04/09/2010 - 09:01
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When you say you have a VLAN overlapping you mean you have the same VLAN number in two network segments?

Or you have an IP overlapping issue?

VLANs are layer 2 in terms of the OSI model

IPs fall in layer 3.

Anyway, there's no way of having any kind of overlapping without virtualization.


wonderpug Fri, 04/09/2010 - 09:10
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Sorry i didn't make this clear. For example two vlan created in the same switch...

Vlan 1, with IP address 

Vlan 2, with IP address

computer connect in vlan 2 and server in vlan 1. This may seem bizzard but assume it's configured in the switch. I would like to know how does it conflict when packets route in the switch.

Federico Coto F... Fri, 04/09/2010 - 11:33
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Both devices will have communication through the switch as per being in the same subnet.

The thing is that it is not a good practice, since the design recommendation is to have 1 VLAN per IP subnet per broadcast domain.

Someone said that VLANs does not exist (is just a concept that switches know about).

And in this scenario is true, since both devices will talk to each other as per being in the same subnet.



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