Gigabit good but 100M and 10M very slow

I work in a 30 workstations company.

I've replaced an old hub on which every one was connecting at 100M / Half duplex for a brand new Allied telesys gigabit switch model AT-GS950/48

Everything seemed to be working fine, but some users began complaining about slow startup time of a network application.

Upon investigation, I discovered that every workstation connected at 100M Full (or below) gets very erratic connection speed, moving from 6Mbytes/sec to under 300Kbytes/sec, back and forth all the time.

Gigabit connections on the other hand, gets very stable speed over 30Mbytes/sec.

The Internet connection is going through a pfSense router which is splitting it in 3 VLANs.

The switch is in production now, so I have little lattitude in terms of testing. Any idea what the problem is?

Thanks in advance.
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I would start by checking the port statisics for any errors.

You could try setting the rate limiting for broadcast and multicast to a low number as well in case there is some kind of issue with the amout of those types of traffic.

I would also turn off any flow control that may be set on the ports.
There might also be issues with speed/duplex negotiating between the gig ports on the switch and the workstations.

If you know they are not gig speed i would suggest also changing the port setting down to 100/full or 10/full whatever the workstation needs.
Yes, this is most likely a duplex setting issue.  Make sure all devices are running Full Duplex at whatever speed they support.
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wznAuthor Commented:
I've tried every possible combination of speed / connection / duplex and always get same result : everything is slow, except 1G links. I tried forcing the switch and it didn't change anything but maybe I have to reboot it for it to take effect ; i won't be able to do that during working hours.

Using the switch management console, I see very few "non-unicast" packets and almost no errors. All flow control are off.

Could a tool like cacti help me get more information?

if I plug a cheap gigabit unmanaged 5 ports switch between a 100M station and the main switch the problem goes away.

if I plug a cheap 100M unmanaged 5 ports switch between a 1G station and the main switch the problem appears.
This really sounds like the switch is having issues negotiating speed/duplex with the workstations. I bet it is setting to 10/half. check your workstations (or switch if you can see it) to see what the speed duplex is negotiated to.

If this is the case and you can not hard set these settings in the switch i suggest contacting the vendor to see if it is a hardware issue or limitation.

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wznAuthor Commented:
The connection speed reported by the workstations AND the switch concurs. EG.: a workstation with a max speed of 100M will connect at 100M, reported as so by both the workstation and the switch.

Same thing if I force the workstation to connect at a lower speed/duplex.

I don't see to be able to use the switch to force the connection speed though. IE.: any speed i enter i the switch, it will connect to the max workstation speed. This is the reason why I think I may have to reboot the switch for the setting to take effect. This seems to be very common with that switch : a reboot is requiered but you are not warned about it.
wznAuthor Commented:
I've rebooted the switch, explicitely setting the speed of one of 100M workstation to 100M-Full.

That didn't have any effect whatsoever, so I'm now doubting it's a duplex setting problem.
wznAuthor Commented:
just tried phoning the company they offer 2 options :

- support contract

They are absolutely no help otherwise.
Iain MacMillanIT Regional Manager - UKCommented:
if you have fixed the speed at both ends, on the workstation and the switch port, you do indeed look like you have an issue with the switch.  i would try another brand of switch if possible - such as HP Procurve, 3COM or Cisco (plenty of refurbished devices can be bought cheaply for testing).

you may also want to check the workstation's driver website and see if there is a newer NIC driver, which may 'talk' better with the switch.  Or perhaps firmware update for the switch.
wznAuthor Commented:
I finally bought a HP procurve switch 1810G-24 to see if it would solve the problem and it did solve it. In addition the switch is fanless, which is so much better near anyone's hears.

So the switch was defective. Luckly I managed to get a refund from my reseller and will go procurve for my current networking needs.

Thanks all.
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