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2 vlans, 1 internet modem on Cisco SF200

I recently bought a Cisco SF200. I'm unfamiliar with the whole vlan topic. We have 2 departments. I want to create 2 vlans, that share one internet connection. We have a standard Cisco Cable Modem.

Can someone please advise on how to get this up and running?

Current setup is, like this:

VLAN1 = default

VLAN10 = port 1,2,3

VLAN20 = port 4,5,6

Cable modem is on port 24.

Please advice. Thanks in advance.


  • Small Business Switches
Everyone's tags (2)

2 vlans, 1 internet modem on Cisco SF200

Hello Sidney,

My name is Chris from the Cisco Small Business Support Center.

There is one problem with your current setup.  The cable modems generally do not support VLANs, so in order to setup two seperated networks like you are describing you will need either a Small Busines router that supports VLANs, or a layer 3 switch, like the SF300. 

The SF200 only works at layer 2, meaning it cannot do the routing for that other VLAN.  Since the modem doesn't understand VLANs either you will really only be able to use one VLAN that covers the same subnet as the modem is handing out.

With a VLAN capable router you can setup what we call router on a stick with your current switch where both VLANs are carried over one link to the router and the router then routes the traffic appropriately.

You can also get a layer 3 switch, which would allow you to do the routing for those VLANs on the switch itself.  However I am not sure if your Cisco modem does NAT, which is what translates your private subnet ( into a publicly routable internet address ( for example).

So the simplest solution to acoomplish what you would like to do would be to purchase a VLAN aware router and then setup a trunk link with both VLANs to the switch.

All of our RV series router can do VLANs and trunking, with the exception of the RV016, RV042, and RV082.

You can also give us a call at 1.866.606.1866 and we would be happy to discuss your options if any of this isn't clear, or to help set it up.

Thank you for choosing Cisco,

Christopher Ebert


Senior Network Support Engineer - Cisco Small Business Support Center

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