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i would like to build a gigabit network to connect the different computers at my home. I already have an 100Mb adsl router/modem but i have an hard time to find a 1000Mb one, so i came up with the idea of using a normal 1000Mb router or switch to put between the adsl modem and the computers. So i only use the adsl modem to connect to the internet and the gigabit router as dhcp to connect the different computers.

But to get to the question. Will the 100Mb adsl router slow down my network? Will data travel like pc > gigabit router > computer or pc > gigabit router > adsl router > gigabit router > pc.

My gut says it will go like in the first option but i have seen network hardware do some weird stuff.

What do you think?

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The "router" name applies if it is routing traffic between diffrent networks. In your case this means routing between your internal network, and the public internet. Your "adsl router" actually also contains a 100Mb switch, which just switches the traffic between the local network, and routes it out over the internet when needed. Its basically 2 network devices slapped together in one housing, 3 if you allow for the adsl modem it contains.

You can just buy a gigabit switch and plug the adsl router into it. If you set the adsl router to do dhcp like normal the workstations will broadcast dhcp requests that'll reach the adsl router and they'll get told by the router to use the adsl routers ip as their 'default gateway' (as normal). such a setup will give you 1Gb traffic between workstations, 100Mb to the adsl router (not that youll likely trasfer files to it) and the internet connection speed will determine the link speed the other side of the router (obviously!)

On my home network I have 4 old "adsl routers" which I use for the features they have (one as a print server, 2 as wifi access points, etc) without actually attaching the internet to them. I hang them all off a cisco gigabit switch. As long as your default gateway is set to the right device (the live router) you'll be dandy.

edit: just remember if/when you buy the switch youll need at least number of workstations + 1, as the adsl router will be off it also.

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The ADSL Router will only determine speeds outside of your network. As long as its connected correctly.
Your PC's will connect to each other through the GB Switch at 1Gbps

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The switch will run each port at its maximum capable speed. The speed of the interconnect between each port is independent of the speed of the ports, and is usually much faster (on the order of 10Gbps+).

As for the actual packet situation, each machine will send packets destined for the local network out on the bare interface without a gateway, which will let the switch figure out the best way to route them (meaning that they won't go through the router).

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