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# What determines maximum network speed?

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This should hopefully be a quick and easy question to settle a bet. What determines maximum bandwidth of a network with the following configuration?

Primary router uses a 10/100 switch. Modem is connected directly to the router. The switch of the router has just a single connection into a gigabit switch. All hardwired devices are connected through the gigabit switch. Half the devices are DHCP, and half are static.

What is the maximum speed from device to device? Is it 1000 Mb or 100Mb? Does it matter if one device is DHCP and one is not or would they all have the same maximums since they are connected to the switch (or lowered because they are also connected to the router?)
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Commented:

You have to be carful with bits and bytes here.
The maximum throughput of data from device to device, on a gigbit network is 125 MB/s
Check this out:
http://en.wikipedia.org/wiki/List_of_device_bandwidths

DHCP does make a difference initally, but generally your talking miliseconds difference between having DHCP on or off. This will generally not affect your throughput speed. Usually things like network interfaces, how fast the router can preform functions such as NAT, disk, ram and CPU speed in both computers.

Becuase your items are connedted to a gigabit switch, between them, they wil transfer at gigabit speed. If any network traffic is going our via your router (internet im guessing) then it will be bottlenecked to 100Mb/s.

http://www.tomshardware.com/reviews/gigabit-ethernet-bandwidth,2321.html

Commented:
Assuming all the devices themselves have gigabit network cards, then the max speed would be 1000Mb/s.  Actual max throughput is less of course due to overhead.
When figuring speed, you need to find the lowest throughput along the path.  Note, SOME gigabit switches are a bit dumb and slow down the entire switch the the lowest speed connected.  If the router connection is 100Mb/s, then a poor quality switch might throttle down.  It shouldn't, but there are a few "cheap" switches that do.
IT Associate

Commented:
Hi,

You can check the speed or total available bandwidth using IPerf;

http://openmaniak.com/iperf.php

As mentioned above, if all devices including your NIC, cables (UTP-CAT5 supports upto 100 MBPs where as CAT-6 supports gigabit), router interfaces and switch ports support 1000 MB/s then you will achieve a maximum speed of 950 MB/s with some speed lost due to overheads but if it is a hybrid of 1000 and 100 MB/s  then your speed will be lesser then 100 MB/s.

Commented:
Thank you for the great answers. I am aware of the difference between actual and theoretical transfer rates.  Am I correct in seeing Uetian1707 disagree with the other 2 answers? Since my stance for the question held with the other two, I just want to make sure that I am not accepting their answer based on my belief. Uetian1707, are you saying that you believe that since since the router is connected 10/100, then the entire network is brought down to that speed even though all devices (except router) on the network are connected to the gigabit switch.
Commented:
I think he's saying the same thing but it's getting a little confused.  With proper switches, they will maintain a point-to-point connection between any two devices plugged into them.  So if two gigabit devices are connected to the switch, they will communicate at gigabit speeds regardless of whatever else is connected to the other ports.
Now obviously other things can impact this.  Poor quality cables might reduce the speed due to errors at the gigabit rates.  Note, cat5e (in fact, even cat5 at the lowest end) are rated for gigabit, not just cat6. And as I mentioned, a low quality switch might shift down depending on what else is plugged into it.

Commented:
Again great answers to all of you. Looks like I win. :) The Netgear FVS318, which we use,  is a fantastic VPN router for the price, but I am amazed they haven't upgraded it to have a gigabit switch built into it.