2 VLANS 2 networks on a layer 2 switch

Unanswered Question
Feb 15th, 2007


I want to setup my layer 2 switch to have 2 different VLANS and 2 different networks. For example



I have only one connection to my router. which is

I know I can setup the VLANS. My question is, do I need a layer 3 switch to do this? Since I'll have two different VLANS with Different IP's that will need to be routed. I'm thinking I do, but wanted to check with the experts



I have this problem too.
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sundar.palaniappan Thu, 02/15/2007 - 13:50


Your understanding is correct. To route traffic between VLANs you need a layer 3 switch/router. However, if your router supports dot1q/isl encapsulation then you can setup a trunk between the switch and the router and make the router forward traffic between the VLANs. This feature is called router-on-a-stick.



MICHAEL CICCONE Thu, 02/15/2007 - 15:07


Thanks for the help. I have a 2620, which is pretty old. I'm not sure if it supports dot1q/isl encapsulation or not. I'll have to check that out.

Thanks again


sundar.palaniappan Thu, 02/15/2007 - 15:29

It depends on what version IOS you are currently running in the router. I believe you need an IOS with atleast an IP Plus feature set for this. Try this;

R3#config t

Enter configuration commands, one per line. End with CNTL/Z.

R3(config)#int f0/0.1

R3(config-subif)#encapsulation ?

dot1Q IEEE 802.1Q Virtual LAN

isl Inter Switch Link - Virtual LAN encapsulation

tr-isl Token Ring Inter Switch Link - Virtual LAN encapsulation

As you can see from the above output, the router would show you whether it supports this feature or not.



MICHAEL CICCONE Fri, 02/16/2007 - 06:49


Currently, my IOS does not support this feature, but now I know I can upgrade and do what I need to do.



ahmednaas Thu, 02/15/2007 - 13:55

You do NOT need an L3 switch to do VLANs. You need an L3 switch or a router to route between them.

What type of switch and router do you have?

MICHAEL CICCONE Thu, 02/15/2007 - 15:05

I have a 2620 Router. currently the switch is a foundry switch, but I will be replacing it with a cisco 3524 or 3550. I know the 3550 will do layer 3 so I can go that way. I just wasn't sure if I had a true layer 2 switch if I could do what I wanted to.

devang_etcom Thu, 02/15/2007 - 15:11

as far as VLAN configuration in layer2 switch you can do... i mean you can configure the VLANs on LAYER 2 switches... but when ever you are talking about the routing between two different VLAN then you have to have Layer 3 device...

if you have router then you can have intervlan routing by creating subinterfaces... and if you have layer3 switch then you can go for the SVI interfaces...


If you have foundry switch then you can have only dot1Q encapsulation as ISL is the cisco propritery...

please rate the post if it helps...



MICHAEL CICCONE Fri, 02/16/2007 - 06:48


Thanks for the help... This is what I was looking for. I just need to update my IOS and this will work. Thanks again



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