Silly but serious question about VLANs

[djcoleschmi]

Hello,

I won't mention specific hardware in this post... Hopefully I can state this question in a way that makes sense.  This a pretty much a hypothetical question, bear that in mind.

I was configuring a new layer 3 switch at my desk; I created VLAN 2, and gave the VLAN 2 interface the IP of 10.2.0.2 /16.  I have a testing laptop, and I plugged it into one of the switch ports on the new switch.  I made that port a member of VLAN 2.  I also made a unused port a member of VLAN 2 (It will get used in a minute)

Our existing network, which happens to be in the same subnet, 10.2.0.0 /16 - is all on the default VLAN 1 - no trunks anywhere, no tagging of frames.

The default GW for out LAN is 10.2.0.1 /16.

Here is the question:  If I connect a port on the new switch that is on VLAN 2 to a port on the existing switch that is on VLAN 1, shouldnt I be able to ping my GW still (From the test machine whos port is also on VLAN 2, and has an IP of 10.2.0.5 ...) ?

Basically, how do the switches know any different if there arent any trunks/tagging involved? ( the ports are in access mode on both sides)

  I understand much, and I have setup VLANs before, router on a stick, trunks...etc.. but for some reason I cant remember why this wont work...and my boss thinks it should... no tagging is taking place...

Also, there is a dumb unmanaged switch in between my new switch and the existing one...maybe that is why?  Details..?  if the dumb switch was there would it then work?

I am only asking for my knowledge, I am not trying to deploy a production setup like this.

Your replies are greatly appreciated !

[jimmysands73_2]

I might not understand your question, and you probably know this already, but arent they member of diff vlans?, therefore the CAM tables keep track of what MACs are associated to what VLANs/ports.

And the dumb switch, you have to make sure its VLAN aware.

[Amit Singh]

Cole,

Please see my earlier post on the same.

https://supportforums.cisco.com/message/3268888#3268888

HTH,

Please rate if it does.

-amit singh

[cadet alain]

Hi,

I have labbed something similar( see diagram) on GNS3 and it worked.I should work also with real gear and even with a dumb switch in between.

Regards.

Alain

[jimmysands73_2]

Great post Amit...cleared up some of my doubts also.

[milan.kulik]

Hi,

what you are talking here about is VLAN interconnectiong via access ports.

It's not a best practice.

But it works as long as STP ensures a loop-free topology.

You are creating a big common VLAN so (with one STP tree) where each device can communite to others via L2.

Each switch "think" the devices belong to "his" particular VLAN, even while they belong to the other VLAN possible when connected to other switch physically.

Jut be careful when using a dumb switch - it might not run STP and create loops in your topology.

HTH,

Milan