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Basically I would like to know if the transfer speeds would be any faster between 2 computers if an additional Ethernet cable was added into a network between 2 switches, which are both connected to a router. Each computer would be on a separate switch. See diagram

diagram

Obviously I know there would be other bottlenecks within the network such as bandwidth limits on the switches and the speed of the interfacing and cabling.

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What are the speeds of the two switches, and how fast is the switch on the router? –  cpast Mar 22 '13 at 18:45

3 Answers 3

up vote 5 down vote accepted

You use a generic term 'router' in your question. But I am going to assume by router you are talking about a typical router design for consumers which will basically include one interface that connects to the upstream network, and the internal side of the router is presented on a 3-6 port switch/hub.

You should treat consumer routers as if they are two/three devices Switch + router + wireless access point. So assuming you are talking about a consumer router, you should ignore the fact that it has a router feature, and possibly wireless AP feature. From the perspective of the switches it is simply another switch, and you have 3 switches in a triangle.

If these 3 switches do not support spanning tree, then you will kill your network because you have created a switch loop.

If your devices do support spanning then one of the links will be disabled to prevent a loop. If the algorithm is operating properly, then the slower 100MB link will be deactivated instead of the two 1GB links.

So a full mesh setup (each switch is connected to other two) gives you some redundancy, but it does not give you additional bandwidth.

If you needed additional switch to switch bandwidth, then you would typically would do that with bonding. This allows you to combine the bandwidth of multiple links (with certain restrictions). Bonding requires a more advanced switch then you will typically see as consumer equipment though.

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I did think this but colleagues disagreed. –  Andy Mar 22 '13 at 19:07
    
you will benefit if one of the other connections failed –  ratchet freak Mar 22 '13 at 21:27

If your switches are 1Gb switches, and your router is 100Mb, then yes, it will increase the speed because the switches will see that the two computers are on the same collision domain and will route the traffic directly to the other switch/device without pushing the traffic through the router.

If possible, it would be best to connect the two computers to the same switch...

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In this scenario both switches are 100Mbps and the router is 1gbps. The switches are both un-managed. –  Andy Mar 22 '13 at 18:55
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Well, then the so called bottle neck are the switches. To me it would make more sense to upgrade them to 10/100/1000 and make sure the NICs in both computers are Gig –  Darius Mar 22 '13 at 18:59
    
That also depends on what the router is. Just because it's a GigE interface doesn't mean it can actually move that. But yeah, the switches are likely more the issue than the router. I would not put that cable in. If you do try it, remove the uplink from that switch to the router. –  LilCodger Mar 22 '13 at 19:51
    
@Andy: Most unmanaged switches do not run spanning tree, so this configuration would be fatal. If you're lucky, the router would figure it out anyway and disable one link, but you might not be so lucky. –  David Schwartz Mar 22 '13 at 22:11

You could certainly see lower latency (ping times). However, once the connection is established, the switch should have minimal impact on throughput. The exception would be if the router's switch is slower than switch 1 and switch 2. In that case, directly connecting the switches would increase transfer speeds.

A lot of home routers have 100 Mbps switches, and a lot of third-party switches are 1 Gbps, so in that configuration, the speed would increase. In general, it's just bottlenecked to the slowest switch or NIC in the path.

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