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I would like to create 2 separate VLANs using a Cisco SG200-series smart switch (layer 2) where the devices would not see each other, while being able to connect to the internet.

The setup is simple, the router - Thomson TG789vn - acts as the DHCP server and plugs into the switch (port 49). The client devices connect to other ports of the switch.

What I tried is changing the router port interface to General and adding it to both VLANs as untagged (see screenshot:)

Port to VLAN mapping

The devices on the default VLAN (1) work fine, however devices on VLAN 2 (e.g. port 38) have no connection (do not receive an IP from the DHCP server, cannot ping it).

The DNS Server configuration does mention VLAN 1 interface though:

DNS configuration on switch

Is this possible without any additional hardware and if yes, how should the setup look like?

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The Thomson (Technicolor) TG789vn supports IEEE 802.1q VLAN bridging according to the datasheet.

The Cisco SG200 supports Port-based and 802.1Q tag-based VLANs.

So, yes, you can set up what you want without additional hardware, although I don't think that everyone would consider the Thomson easy to set up for this task. You are setting up a standard two-LAN solution with a router connecting them both to the third network (the internet/WAN). In a normal scenario the router would also connect the two LANs together, but this is easy to block with a bi-directional firewall rule.

marco has provided a comprehensive article on setting up the TG789vn with VLANs here http://www.cyberhq.nl/article/327/really-bridging-a-thomson-tg789vn. Note that the management interface for the router will only reside on one of the VLANs. You will need to research if you can set up a second DHCP server on the router for VLAN 2 or if you would need to set up a second DHCP server.

It would probably be easiest to set up the two VLANs on the router to use two separate ports without tagging and connect them to two static access ports on the switch in two separate VLANs. You would then choose which VLAN to put each of the other switch ports into so that your devices connect to the right network.

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