Simple (I hope) question re: gigabit switch

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mgbridges

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#20930 10-Apr-2008 11:33

Hi folks,

I'm trying to take an evolutionary path to a decent home network, mainly because funds are somewhat limited. At the moment I have a Vista laptop and Ubuntu desktop sharing (via wireless) a broadband connection through a Netgear DG834 modem/router. Both the laptop and the desktop have gigabit ethernet capability so what I was thinking of doing was adding a gigabit switch and running ethernet cabling to the various rooms I may want to have PCs in future (e.g. as media centres).

My simple question is, can I just connect my DG834 (non-gigabit) modem/router to a port on the gigabit switch? I realise that the link from the gigabit portion of the network to the internet will therefore just be 100Mbps, but that's faster than the outside world anyway so it shouldn't be an issue.

Thanks in advance for your help.

Martin

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#122507 10-Apr-2008 12:19

Yes, you can. That's what I have here at home - all laptops, media center, iMac have gigabit and it's great to share with the Windows Home Server, and the cable modem plugs into the gigabit switch.

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mgbridges

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#122510 10-Apr-2008 12:29

Cool -thanks for the quick response.

tonyhughes

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#122511 10-Apr-2008 12:34

You are on the right track... as long as a particular cable/port combination supports the throughput you need/want through it, you are fine to mix and match!

richms

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#122571 10-Apr-2008 16:22

I would approach mixing with caution. I have had loads of problems when plugging a gigabit lan into a 100 meg one with the frame size not backing down automatically to the machines on the 100 meg segment as you would expect it to. Without jumbo frames there is only about a 2x speed improvement with gigabit over 100 meg IME, with the jumbo frames it will saturate the gigabit connection easily.

If you have problems then the first thing to try is to limit the size of the frames on the gigabit adapters to see if that solve it, if it does (as it did for me) then I have no idea where to go from there unfortunately.

Richard rich.ms

tonyhughes

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#122587 10-Apr-2008 16:41

I know many people with Gbit switching who limit their client PCs to 100Mbps, even if they have Gbit cards. Individual performance comes down to 100Mb level (ie. 70-80Mbps actual), but overall network 'happyness' ("Is that the technical term", Tony wonders to himself) improves.

tonyhughes

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#122588 10-Apr-2008 16:41

tonyhughes: I know many people with Gbit switching who limit their client PCs to 100Mbps, even if they have Gbit cards. Individual performance comes down to 100Mb level (ie. 70-80Mbps actual), but overall network 'happyness' ("Is that the technical term", Tony wonders to himself) improves.

Of course I am talking about unmanaged, entry level gear here...

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richms

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#122593 10-Apr-2008 16:49

When I had everything gigabit and a 7k frame size, it flew along between the desktop and the file server, but moving stuff out to the garage and loft and only owning one gig switch meant that lots was on 100 meg, and thats when things went to crap. I even put 100 meg cards in the machines connected to the 100 meg switch incase it was thinking it was jumbo frame clear since the card could do it.

Still no dice. I have never had a problem with the switches choking on several 100 meg streams going across them between machines, and thats a real cheap one with no QOS or anything.

Richard rich.ms

mgbridges

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#122594 10-Apr-2008 16:50

richms: I would approach mixing with caution. I have had loads of problems when plugging a gigabit lan into a 100 meg one with the frame size not backing down automatically to the machines on the 100 meg segment as you would expect it to. Without jumbo frames there is only about a 2x speed improvement with gigabit over 100 meg IME, with the jumbo frames it will saturate the gigabit connection easily.

In my planned network the only thing on the lower speed segment would be the ADSL modem/router. Should this be OK? I'm trying to avoid the outlay on a gigabit modem/router, since the one I have works fine.

Martin

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#122597 10-Apr-2008 16:53

I only had problems copying across the lan, where it would go very very slowly to some PCs with the server set to a larger frame size. Internet was uneffected, so I am assuming that the MTU negotiaion of the router was working as it should, unlike between the windows PCs on the lan.

Richard rich.ms

mgbridges

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#122605 10-Apr-2008 17:05

richms: I only had problems copying across the lan, where it would go very very slowly to some PCs with the server set to a larger frame size. Internet was uneffected, so I am assuming that the MTU negotiaion of the router was working as it should, unlike between the windows PCs on the lan.

In my case all the PCs would be on the gigabit portion of the network, so it sounds like I should be OK.

Thanks for the advice.

Martin

richms

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#122613 10-Apr-2008 17:32

You can always limit them to the normal ethernet frame size, it just means you will see longer copy times for large isos and dvd rips across the lan, its still enough for a 16x burn off the filesever with the small framesize, its just that when people come over and want to fill their 320 gig laptop drive it will be slower, but really, thats not my problem is it ;)

Richard rich.ms