Vlan and trunking question

Quick question so I can clear this up in my mind concerning dot1q and the need for tunk ports.

So lets say I set up a network I have 4 switches.

3 switches are layer 2 only the 4th switch is a layer 3.

on the layer 2 switches I configure a separate vlan on each switch so

switch 1 VLAN2
Switch 2 VLAN3
Switch 3 VLAN4

I connect each switch to a seperate port on my layer 3 switch and configure each port for the corresponding VLAN. The layer 3 switch will take care of inter VLAN communication through routing. So in this instance, assuming no use of VTP, I would not need to use a 802.1q trunk port as I have each switch set up with only one VLAN.

However change out my layer 3 switch and replace it with a router with only one physical interface. I configure the router fastethernet interface with multiple subinterfaces to route between my VLAN's and since I would need multiple VLAN's to traverse one physical link I would have to configure 802.1q trunking on this.

is my understanding on this correct?

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Comments

gojericho0

Yes that is correct. The VLAN from each L2 switch would terminate at the L3 switch. If trying to reach another L2 switch, the L3 switch would then route to the next SVI and and send it out the appropriate VLAN port

mikej412

bestialwarlust wrote:

However change out my layer 3 switch and replace it with a router with only one physical interface. I configure the router fastethernet interface with multiple subinterfaces to route between my VLAN's and since I would need multiple VLAN's to traverse one physical link I would have to configure 802.1q trunking on this.

Correct -- but you would also need trunks between the switches so that traffic from the other switches can reach the router.