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The environment I'm working in has an EdgeRouter and a single switch (EdgeSwitch 48).

They are looking to add another EdgeSwitch and connect both switches together for a single broadcast domain.

However, is it possible to connect both switches together, and then connect both switches to the router? The idea is that internet traffic will go directly from either switch to the router, but LAN traffic can go directly in-between switches.

  • You can virtualize using mclag or run the switches on active/passive mode. However please provide more detailed question to give you a detailed answer. – user88975 May 3 '17 at 15:11
  • The question wasn't about redundancy, just about expansion. – Zac67 Jul 2 '17 at 17:59
  • Did either answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. – Ron Maupin Aug 1 '17 at 17:35
  • It will surely work since the traffic destined to internet will carry mac address of gateway/router which will reach to it from either switch and for LAN network it will eventually learn which hosts reside at which port. So connecting switches back to back will create a single broadcast domain. – enZyme Sep 1 '17 at 13:39
  • Can you tell us what model of switch and router you are using? – TDurden Sep 2 '17 at 22:21
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Possible to connect each switch to the router and to each other? Yes, but it isn't as simple as just connecting them.

To get the operation you describe ("internet traffic will go directly from either switch to the router, but LAN traffic can go directly in-between switches")? No, not without complicating the configuration of end devices and making maintaining the network exponentially more difficult.

The interfaces on the router will either be L3 interfaces (which would require separate IP addresses per interface) or L2 bridged interfaces (which is not recommended - see below).

With L3 interfaces, each interface would have a different IP address. The devices connected to the network will only have one of them configured as a default gateway and all internet traffic would flow through that one L3 interface. The only way to get it to work as you describe is to do something crazy like manually configure GW1 on devices connected to SW1 and GW2 to devices connected to SW2.

With L2 interfaces, spanning-tree should work to provide a loop free environment (L2 loops are bad). This means that all the traffic will either flow from switch to switch then out one router interface or all traffic between switches will flow through the router.

Personally, I would connect both switches to the router and to each other, but simply for redundancy. Use L3 interfaces and run VRRP between the interfaces. Each L3 interface has it's own IP address and then "float" an IP between them, which would be the gateway. If you have a problem with one link to the router (one of the switches dies, cable gets disconnected, etc), then internet traffic will still be able to flow out the other L3 interface.

Finally for the note on bridging; bridging is discouraged by the vendor (at least for some Edgerouter platforms):

It is generally discouraged to enable bridging because traffic which is bridged is not hardware-offloaded, and will cause a decrease in performance. It is highly advised to use a dedicated switch connected to one of the LAN interfaces to allow for multiple ports of connectivity to the LAN rather than bridging.

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Short answer: yes.

The easiest solution is to connect the new switch to the existing one. If you're not looking for redundancy or need to remove a bottleneck from the network, that's all there is to it. Most often in small networks, a single gigabit link can easily carry all the traffic there is, whether it's between the switches or with the outside world through the router.

However, if you're looking for redundancy or performance increase, you'll need to explain your situation and your goal in a more detailed way.

E.g. when using two router ports, one for each switch, the difficulty is to get the clients from the one switch to use the one port as default gateway and the clients from the other switch to use the other port. If you set up all clients manually, you can configure them in that way, but using DHCP you'd need to figure out a way to pass them different default gateways.

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The usual way would be to use two edgerouter sockets as a switch and connect the two switches directly. If that's not practical for wiring reasons, then you chain the switches together as has been already suggested. I'm guessing there are no significant performance considerations. If you're after resilience of cable/switch breakages, read up on spanning tree.

 inet
  |
router
 |    |
sw1  sw2
|||  |||

Hope that's helpful

Jonathan.

  • To get a single broadcast domain with the two switches would require that you put the Edgerouter ports going to the switches in bridge mode. This is against the vendor recommendations as it has a significant performance impact. See my answer for more detail. – YLearn Oct 3 '17 at 16:10
  • @YLearn you're right, of course. Nonetheless might well find that performance isn't too significant here. – jonathanjo Oct 3 '17 at 19:23
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Routers route between network, so each router interface belongs to a different network. Since you cannot connect both switches directly to the same router interface, you would be connecting them to two different networks.

Also, switches use spanning-tree in order to create a single, loop-free path on the layer-2 LAN. In order to do this, all switch traffic is sent to the elected root switch. A switch has no idea which packets are destined for the Internet because all layer-2 traffic is local. Switches know nothing about your layer-3 addressing.

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Yes, you can!

You can connect the second switch to the first one and extend your network easily. However, this network which is called "daisy chain network" is not recommended since your network would be more vulnerable. If anything happens to the first switch, the rest of the network would be affected. Although this type of network is not recommended, there are lots of people/small companies using this solution and they are happy with it as they don't want to do anything special with their network and just connecting to the internet and having a reasonable internal connection between the clients is enough.

So if this is the only thing you wanna do with your network (which I assume it is, based on your question), you are safe to connect the second switch to the first one and build a daisy chain network :)

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I'm not sure if your hardware will support it, but my preferred setup is to stack the switches so they are logically one switch.

Then you can use two interfaces on the router in a port channel with one physical connection to each physical switch.

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Yes, but don't. Simply daisy chain the new switch off the existing switch. Any other configuration is over-engineered and violates the KISS principle.

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