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[SOLVED] Net communication via switch or router
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marco.difresco
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PostPosted: Mon Aug 14, 2017 12:27 am    Post subject: [SOLVED] Net communication via switch or router Reply with quote

Hi all,
I am sure it is a noob question, but it is something that is bugging me for some time. :oops:

On my house I have a central router that acts as DHCP, share the DSL connection, and does all other router stuffs (port forwarding, etc.) and since the house is big, it connects to two switches that then connect to the individual computers. I am using a single subnetwork (192.168.0.x).

My question is: once they got their internal IP from the router's DCHP, do the computers behind the same switch communicate through the switch only or does all the traffic still has to pass through the router? Of course I am referring only to the eventual direct traffic between these computers as I realize that the traffic to the internet and to the computers behind the other switch still need to pass through the router.

I ask because the other year I took advantage of some restructuring inside my house to install CAT6A cables through the walls for forward compatibility toward a future 10 Gbps LAN and I am planning to upgrade the individual computers' network cards, switches, and eventually the router when the prices will lower down (and of course my savings grow up :D ), but it will be gradual; therefore it would be nice to know if I upgrade a switch at least the computers behind it will benefit the full 10 Gbps speed even if the router is still at 1 Gbps.

Thanks in advance.
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Last edited by marco.difresco on Mon Aug 14, 2017 4:17 pm; edited 1 time in total
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ct85711
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PostPosted: Mon Aug 14, 2017 1:26 am    Post subject: Reply with quote

The way the switch works is that it checks to see if the target computer is on that switch, if it is, the switch will just direct the traffic there and not bother with the router. When the destination is not on the switch, it will send it on switch, it will send it off towards the router or other switch.

This is going with the assumption your network is laid out like this:
Code:

                              Router  ------   Internet
                              /     \
                            /        \
                       Switch1     Switch2
                       /                 \
                    Comp1              Comp2


Last edited by ct85711 on Mon Aug 14, 2017 1:27 am; edited 1 time in total
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russK
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PostPosted: Mon Aug 14, 2017 1:27 am    Post subject: Reply with quote

The traffic between nodes on your LAN on the same switch does not have to go through the router. If I'm not mistaken, with pretty much any modern switch nowadays you can run a single cable from one switch to the other. You don't have to necessarily run a cable from the router to each switch. Instead, you could run a cable from the router to only one switch, as long as there is a cable between the switches. I suspect the way you have it, the router is also acting as a switch. Most routers are designed to do that as well. Having said that, you may want to avoid running a cable between the switches if there is also a cable from each switch to the router. Personally I would only do one or the other.

HTH
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PostPosted: Mon Aug 14, 2017 8:14 am    Post subject: Reply with quote

marco.difresco,

Lets consider a hub first. A hub and switch look the same and appear to work the same but hubs are dumb and switches are smart(er).

A hub sends all packets that arrive at it to all ports. Something on one port will know what to do with the and everything else will ignore the packets.
That's dumb as it clogs up your network and wastes bandwidth.

Switches learn what is connected to each port, so they only send packets where they are needed.
This is good for your network bandwidth and your privacy. Its harder to monitor network traffic between two systems on a switch than on a hub, where everyone gets everything anyway.
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tld
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PostPosted: Mon Aug 14, 2017 1:17 pm    Post subject: Reply with quote

ct85711 wrote:
The way the switch works is that it checks to see if the target computer is on that switch, if it is, the switch will just direct the traffic there and not bother with the router.
Yup. I take advantage of that by having my MythTV backend and frontend computers, as well as my HDHR tuner connected to the switch, making the whole system pretty much immune to router reboots etc.

Tom
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marco.difresco
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PostPosted: Mon Aug 14, 2017 4:17 pm    Post subject: Reply with quote

Hi all,
thanks for your answers.

To clarify (even if you got my question right), I adapted "ct85711" diagram to my network and it look this:

Code:

                            Router  ------   Internet
                              /   \
                             /     \
                            /       \
                           /         \
                     Switch1        Switch2
                       /\              / \
                      /  \            /   \
                     /    \          /     \
                   Comp1   Comp2   Comp3 Comp4


And I am looking to communication like Comp1<-->Comp2 and Comp3<-->Comp4 (any other combination of course require passing trough the router).

And indeed your answers reassured me that the switches are smart enought to handle the traffic below them. :)

Thank you very much.

russK wrote:
The traffic between nodes on your LAN on the same switch does not have to go through the router. If I'm not mistaken, with pretty much any modern switch nowadays you can run a single cable from one switch to the other. You don't have to necessarily run a cable from the router to each switch. Instead, you could run a cable from the router to only one switch, as long as there is a cable between the switches. I suspect the way you have it, the router is also acting as a switch. Most routers are designed to do that as well. Having said that, you may want to avoid running a cable between the switches if there is also a cable from each switch to the router. Personally I would only do one or the other.

HTH


Actually the router is in a central position and the two groups of computers are in the opposite directions to each other from the router, so connecting them both to the router was the solution that required the least cabling.
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russK
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PostPosted: Mon Aug 14, 2017 6:46 pm    Post subject: Reply with quote

Quote:
Actually the router is in a central position and the two groups of computers are in the opposite directions to each other from the router, so connecting them both to the router was the solution that required the least cabling.


That's fine. If you have an extreme amount of traffic between nodes on switches 1 and 2 and are extra worried about privacy, as NeddySeagoon points out ... you could employ yet another switch, Switch3, right next to the router.
Connect the router to Switch 3, and switches 1 and 2 to switch 3.
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