router on a stick with multiple dot1q trunks

Unanswered Question
Sep 20th, 2010
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Can I use the same dot1q tag's on diffrent physical interfaces that go to different switches in VTP transparent mode?

For instance like this:

Router with two interfaces fa0/0 and fa0/1


interface fa0/0

description connected to switch 1

interface fa0/0.1

description vlan 1 switch 1

encapsulation dot1q 1

interface fa0/0.2

description vlan 2 switch 1

encapsulation dot1q 2


interface fa0/1

description connected to switch 2

interface fa0/1.1

description vlan 1 switch 2

encapsulation dot1q 1

interface fa0/1.2

description vlan 2 switch 2

encapsulation dot1q 2

Regards, Peter

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Overall Rating: 4 (2 ratings)
milan.kulik Tue, 09/21/2010 - 00:21
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IMHO, yes, you can.

But if the VLANs are spread over both switch1 and switch2 you would need to configure IP addresses within the same subnet for your router subinterfaces probably.

And this is not allowed by IOS.



Jon Marshall Tue, 09/21/2010 - 03:31
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As Milan says, if these are the same vlans ie. vlan 2 uses the same subnet then no it's not possible because the router will complain about overlapping addresses.

If they are the same vlans why not just interconnect the switches and then just one of the switches to connect to the router using 802.1q subinterface ?


pverstegen Tue, 09/21/2010 - 04:45
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The vlan interfaces are all /30 subnets, it is just that I can reserve the same vlan's for layer 3 interconnect in each switch.

I would like to use this situation for VRF lite configurations where I need many interconnect vlan's between switches.


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