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I have a device that needs to be isolated from broadcast traffic (excess broadcast traffic is causing the device to crash), but the web console on the device still needs to be accessible via a browser. I've purchased a managed switch, created a separate VLAN (let's call it Device VLAN), and associated the port that is physically connected to the device with the Device VLAN. I figured I had taken care of the issue, but I was wrong.

Before associating that port with the Device VLAN, I was able to access the web console on the device, yet after the association I am unable to do the same. I thought maybe I would need to do some port forwarding, but am not finding this as an option for the physical port under the VLAN menus.

I thought this was one advantage of a VLAN - separate from the rest of the network (general-traffic-wise) but still have the ability to access the device directly. Am I wrong? Can someone guide me in the correct direction? The switch purchased is a Netgear GS108T.

A few more details:

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3 Answers 3

You need a router, not a switch.

VLANs let you have two separate networks on the same switch. The two networks won't automatically communicate with each other (broadcasts or otherwise). Just like you need a router to connect separate physical networks, you need one to join VLANs. A router would allow direct connections while blocking broadcasts.

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Can you explain the process with the router with a little more detail? I do have a Linksys WRT120N laying around. Do I keep the switch as a part of the setup? Or ditch the switch and only use the router? If I'm only using the router, what settings need to be made/changed in order to allow the direct connections while ignoring the broadcast traffic? –  MandM Jul 31 '13 at 14:36
    
Also, to the port forwarding part of my question - say the device has address a.b.c.10, and the switch has an address of a.b.c.20, after associating the device with a separate VLAN, could I not forward port 80 of the device, say port 8080, through the switch and access the web server by hitting a.b.c.20:8080? Again, I haven't found that as an option, but I thought that it was doable.. –  MandM Jul 31 '13 at 14:46

Devices in the same VLAN reach each other without needing a router. For instance, if your Internet connection goes down at home, you'll still be able to exchange files between two PCs. The Internet connection you have is part of an external network. Without a router, you won't be able to exchange information between two distinct network.

What you need is a router. If you use a cheap domestic one (I assume it doesn't support 802.1q), you would probably be configuring your switch with 2 ports for the router: one in the VLAN 1 and another in VLAN 2. You would then connect a cable from the port in VLAN 1 to a port on a LAN port of the router, and another cable from the port in VLAN 2 to the WAN port of the router.

After that, you would need to properly setup IP addresses on the router. You would need to configure two IP addresses in different subnets for the LAN and the WAN interfaces. For instance, you could use LAN: 192.168.1.1 with a mask of 255.255.255.0 and WAN: 192.168.2.1 with a mask of 255.255.255.0. Then, you would disable the NAT and any kind of firewall. When you configure the IP addresses of your end-devices, you would use IPs in the same range as the VLAN they're in. If you follow what I wrote above, you could use 192.168.1.10 for a VLAN 1 end-device, and 192.168.2.10 for a VLAN 2 end-device.

You would also set an appropriate gateway, for each device. Devices in VLAN 1 would have 192.168.1.1 as a gateway, and devices in VLAN 2 would have 192.168.2.1. Setting the gateway will instruct the devices to send their packets to the router when they want to reach a network they don't already know of (present in their routing table).

Network Topology

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Are you sure it is broadcast and not multicast traffic causing the crashes? Usually there isn't all that much broadcast traffic on a small/medium network. Multicast traffic however can easily cause some devices to crash due to having to receive it all.

To block the multicast traffic turn on IGMP Snooping. This will stop the sending of multicast traffic on switch ports where nothing attached asked for or wants the traffic.

For the linked switch manual the IGMP Snooping information starts on pages 3-39.

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