Clarification on VLAN Configuration in InterVLAN Lab

[sadikhanM]

I am a bit confused regarding the inter VLAN lab I created with the help of three switches and four VLANs (10, 20, 30, and 40).On SW1, I configured VLANs 10 and 20. SW2 has VLANs 10 and 30, while SW3 has VLANs 20 and 40. On SW1, I configured the trunk port to allow all four VLANs. However, I did configure VLANs 30 and 40 on SW1, as there are no devices connected to those VLANs.  I repeated the same process on all switches, and the ping tests were successful.My question is: Why do I need to configure all VLANs on each switch if there are no devices connected to them?I would appreciate any clarification on this matter. Thank you for your assistance!

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[Joseph W. Doherty]

My question is: Why do I need to configure all VLANs on each switch if there are no devices connected to them?

Why do you say, or know, they are "needed"?

What's the topology between the 3 switches?

What specifically were the successful ping tests?  Any ping failures?

[sadikhanM]

I attached the topology below. Please take a look. There were no ping failures; all were successful. However, I am wondering why I need to configure all VLANs on each switch. In my first attempt, I only configured the VLANs that belong to each switch, not the VLANs of other switches. But since the ping didn't work, I then configured all VLANs on each switch.

[Joseph W. Doherty · Accepted solution]

Besides needing, of course, VLANs defined on switches having access ports in a particular VLAN, you also need same for trunk ports that will be used for transit.

Your left most switch should only need VLANs 10 & 20, middle switch 10, 20 & 30, and right most switch 10, 20, 30 & 40.  The additional VLANs on the latter two switches are to reach the router.