We have a strange network problem on our LAN.

[jheyrman]

At certain times (randomly) our network clients seem to lose their network connection to a server, when this occurs they can't connect to one server but are still able to connect to other servers.
This results in many strange things and errors.

"Disk or network error" (MS-Access)
"Cannot save document you must select another file name" (MS-Word en MS-Excell)
"The file is in use by another user… " (MS-Excell)

As a result of this we started pinging the servers every second from a client PC connected to the same switch as the servers. And we discovered that when this error occurs the server in question gives no replies on the ping command. (Sometimes for more than 15 seconds !)

We discovered now that when we open PcAnywhere sessions to the servers the problem disappears.
When the sessions are open the servers can respond to the ping command at all times and the clients don't lose their network connections to the servers anymore. When we keep the servers very busy (CPU and LAN) then the clients also seem to keep their connections alive.

Here are some specs of the things we have.
Servers:
Poweredge 1300 WinNT 4.0 SP6a (with Intel pro 10/100 LAN card)
Poweredge 4200 WinNT 4.0 SP6a (with 3com 3c980 server LAN card)
Poweredge 2500 WinNT 4.0 SP6a (with Intel 8255xx-based 10/100 LAN card)
Network:
Cisco Ethernet switch model 3524
All servers are connected to this switch and they negotiate 100Mbit Full Duplex.

Things we already tested but didn't help:
We tested with other switches (baystack, 3com) and hubs (Intel)
We changed the cabling.
Forced the auto-negotiation to 100/full 100/half 10/full 10/half
Other network cards (in clients and servers)
Checked out the temp directories on clients (MS KB: Q150943)
We disabled all the power saving on clients (NT4 Server has no power saving)

One strange thing,
We have 1 Compaq sever (Proliant ML370).
This server doesn't seem to have this problem.

Does anyone know of this phenomena or knows a solution?

Best regards
Johan

 

[jgercken]

Maybe something is causing a spanning tree topology change? This would cause 30 seconds of blocking (by default) while the switch goes through the listening and learning modes. Try enabling spantree portfast on all switchports connected to hosts.

I can remember a similar problem we had but I can't think of what it turned out to be. I'll probably dream about it/wake up at 4am in a cold sweat with the answer.

Could be a stuck tcp window maybe. All on same subnet?

-Jeff ----------------------------------------
Wassabi Pop Tarts! Write Kellogs today!

 

[spi200]

Hi

Sounds like a sleep mode on the NIC card - check Bios settings and disable.
I also had some nic cards in Acer pc's which could only be disabled by removing the "wake on lan" cable which connected
the nic to the Lan. They may have been Intel 10\100 carn't be sure.

Regards

David