Gb switch slows download speed

[davej99]

If I connect to my 21CN ADSL Max connection as follows:

(1) PC Gb NIC at auto speed >> Gb switch at Gb speed >> Gb Switch at 100Mb speed >> 100Mb Router.
I get a download speed of 2.4-3.5 Mbps using BT Beta Tester and 1.0-1.2 Mbps with a ThinkBroadband single test file download.

(2) PC Gb NIC at duplex 100Mb >> Gb switch at 100Mb >> Gb Switch at 100Mb >> 100Mb Router.
I get 6.2 Mbps and 6.5 Mbps flat-lining at profile respectively.

(3) PC Gb NIC at auto speed or at duplex 100Mb >> 100Mb Router.
I get 6.2 Mbps and 6.5 Mbps flat-lining at profile respectively

Same behavior with different routers. Can't eliminate my Netgear G5605 switch. Gb NIC to Gb NAS connects through switch at Gb speed. No problem using wireless NIC. Both NIC MTUs 1500. Router MTU1458.

Any ideas 

Thx Dave

[Lance]

Dodgy cable?

[davej99]

Thx Lance.

Get same behaviour with three PC's, XP and Vista, two routers and different cables. If a NIC connects to my Gb switch at Gb - get problem. If a NIC connects to Gb switch at 100Mb - no problem. Can only think faulty unmanaged switch is not handling flow control with a Gb NIC connection. Or perhaps recent exchange conversion to 21CN is not managing flow control with a Gb NIC connection. NIC-NAS at Gb works well and much faster than 100Mb. N-wireless works fine.

Dave

[t22design]

I have a GS605 and it caused much weirdness on my network. Everything appeared to be working fine, but then LAN transfers would slow to a crawl (16MB file in 5 minutes). I tried all manner of diagnostics, cables, computer settings and OS tweaks. The only thing that fixed it was taking the switch out of the network.

[davej99]

Well it looks like the GS605v2 switch was the cause of the problem. I have replaced it with a Netgear GS108v3, which seems a more robust metal cased product, with power saving capability. Comparing this with the old switch it is clear how eratic the old one was in establishing the connection speed. It also seems faster writing to my NAS and I do not get slow broadband download speed when connecting at 1Gb to PC and 100Mb to router. Thx also to Brian in IDNET Tech support for invaluable help above and beyond the call of duty. Thx Brian.