How To Connect 2 Network Switches?

FJWH · Sun Aug 23, 2015 4:54 pm

Hello guys and girls,

Just moved so i had to change everything with my internet connection. I find out that i had more ethernet devices than i thought (although part of them can be connected with WiFi) and i wanted to make things more secure by connecting them with ethernet cables where i can. I made a drawing with two possible ways to connect my devices (I hope the image i added is visible). My question is: what is the best way? In serie or parallel lay out? What is more stable, is there speed lost when you connect network switches in serie? Anymore thought about my lay-out, positioning in the network etc. ?

Thanks a lot guys!

Regards, Frederik

Aesma · Sun Aug 23, 2015 5:12 pm

Does the router itself have a switch (probably yes) ? Is it 100Mb/s or 1Gb/s ?

I would test both layouts with a PC on each switch and transferring data from one to the other, if the router isn't a limiting factor then both layouts should be equivalent.

I used to have the left layout until I realized there were enough Ethernet ports on the ISP box to do away with one switch and only keep the one that is 20 meters from there.

moo · Sun Aug 23, 2015 5:21 pm

Unless your modem/router is high quality, option 1 will allow a greater throughput across devices on the network due to the way switches work.

FJWH · Sun Aug 23, 2015 7:10 pm

Quoting Aesma (Reply 1):
Does the router itself have a switch (probably yes) ? Is it 100Mb/s or 1Gb/s ?

1 Gb/s. I know it has 4 ethernet ports as well but i am not sure if that is called a switch like you said. A friend of mine actually said that option 2 is better in terms of speed. I've read different stories about this so it is difficult to determine which one is 'the best'. I think i have to test it indeed.

I actually want to spend some money for a good router. If i take this quality router , http://www.dlinkmea.com/site/index.php/site/productDetails/789 , would you say option 1 or 2 doesn't matter anymore because of the router quality?

Thanks!
Frederik

sebolino · Tue Aug 25, 2015 8:26 am

I think it depends of the usage of the devices on switch 2.
If they don't need to connect to Internet (except "Desktop"), but need to connect (often) to devices on switch 1, option 1 looks better.
If they need to connect to devices on switch 1, I hope that switch 1 is able to learn several MAC addresses per port, otherwise it will act as a hub.
Now if they need to connect only to devices on the same switch (except "Desktop"), option 2 looks better.

The problem with Option 1 is that frames coming from "Desktop" will cross 2 switches before reaching the modem, instead of 1 in option 2.

But anyway, I doubt the difference will be so big (switches are very fast).

Airstud · Thu Aug 27, 2015 11:13 am

Quoting sebolino (Reply 4):
The problem with Option 1 is that frames coming from "Desktop" will cross 2 switches before reaching the modem, instead of 1 in option 2.

But anyway, I doubt the difference will be so big (switches are very fast).

The problem that I see with option 1 is that needlessly subjects Switch #2 to an additional point of failure.

moo · Thu Aug 27, 2015 12:52 pm

Quoting Airstud (Reply 5):
The problem that I see with option 1 is that needlessly subjects Switch #2 to an additional point of failure.

It provides the lowest chance of frame collisions or congestion on the network however - if you connect both switches to the router, all traffic between devices on those two switches will traverse the router, increasing the chance of congestion on the interconnects between the switches and the router.

If you consider the router as another peripheral rather than network infrastructure, then you can take it out of the equation - the only traffic that should hit the router is internet bound traffic or wifi bound traffic (assuming that is what that symbol off to the right of the router signifies).

Now consider that the internet connection and the wifi connection will *always* have less bandwidth and higher latency than a wired device, and it doesn't matter that the interconnect from switch 1 to the router bears all the traffic destined for those, because its going to run into a congestion pinch point at either of those two spots anyway.

If you connect switch 2 to switch 1, you instantly separate out traffic destined for the internet or wifi from any device on switch 1 (while the interconnect between switch 1 and switch 2 still has to handle internet or wifi destined traffic from switch 2, but again it doesnt matter as its going to hit a congestion pinch point anyway), meaning you have theoretically higher throughput within the network to work with due to a lower amount of traffic...

casinterest · Thu Aug 27, 2015 12:58 pm

I would go with Option 2.
But I would give the Airport Express it's own port off of the Router.

Quoting moo (Reply 6):
It provides the lowest chance of frame collisions or congestion on the network however - if you connect both switches to the router, all traffic between devices on those two switches will traverse the router, increasing the chance of congestion on the interconnects between the switches and the router.

No, Hubs allow for collisions. Switches and Routers do not. Putting them in parallel off the router will allow the traffic to be isolated on switch 1 and switch 2. If switch 1 and Switch 2 are logical switches they will also prevent collisions amongst traffic within their network. The only gotcha is if you exceed bandwidth, and that will only happen if you are pumping a lot more data than I would expect across the network between devices.

moo · Thu Aug 27, 2015 1:12 pm

Quoting casinterest (Reply 7):
No, Hubs allow for collisions. Switches and Routers do not.

Uh, they do actually, there is only so much bandwidth provisioned on the switch and router back planes.

Quoting casinterest (Reply 7):
Putting them in parallel off the router will allow the traffic to be isolated on switch 1 and switch 2.

While making sure *all* traffic needs to traverse the router, not just the traffic that needs to...

casinterest · Thu Aug 27, 2015 1:42 pm

Quoting moo (Reply 8):
there is only so much bandwidth provisioned on the switch and router back planes.

We are talking about GBe Router with a 30-200 Mb Cable modem at best? Bandwidth is not the issue in "Collisions". Bandwidth is taking all the available data with dedicated traffic. Collisions are when all the traffic on the network fights for the available bandwidth with no switch to tell them when they can use it, and no switch to block the traffic from broadcasting all data to everyone on the same network. Call me when it is a 10 MB Token Ring Hub and we can worry about collisions.

Quoting moo (Reply 8):
While making sure *all* traffic needs to traverse the router, not just the traffic that needs to...

Look at that diagram.
He has TV's + Apple TV on switch one and the Airport Express on switch 2. The traffic will be going across his computer network for TV traffic needlessly. Perhaps the Apple TV is hardwired, but you want the Airport express handling the wireless entries at the top of the network, especially since eventually the computer and eventual wireless TV box will want access to the network at the highest level possible.

If it is a 4 port router, I would use all 4 ports for the 4 highest traffic systems in the network that are used and expect the least delay.

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