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Network bogged down - slowing down some client PCs

I am working on a network that consists mainly of 2 stacks of 6 Dell PowerConnect 6224 switches. There are also a few other independent 6224's that connect to the stacks via CAT6 cable. I know when we're having an issue because the lights on the front of the switch will change. Typically they flash fairly slowly and not really in sequence. When they're having an issue, they pulse much more frequently and almost (if not totally) in complete sequence. This seems to be happening on all switches.

It's affecting the network here in that things are running much slower than usual (it's intermittent on some workstations). Mine seems completely unaffected. Others are slow in opening network applications, printing, and even some are slow opening local apps (Word, Excel, PPT).

The switches have spanning tree portfast enabled.

The network had been running fine until last Friday and I honestly can't think of anything that changed.

How can I find the source of this problem and get it corrected?
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street9009
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street9009
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1 Solution
 
Lee IngallsDirector of IT/TS, Quality and FinanceCommented:
On the switch -- check the port statistics of the workstations that are experiencing the intermittent issues.
Are those ports experiencing packet errors/loss/drops?
What is showing up in the Event Viewers - Windows Logs of those same workstations when you filter for Critical, Warning, Errors?
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street9009Author Commented:
It's a lot of workstations. I don't want to underestimate how many it is but I'd say it's more than half of our network (some are just more vocal than others obviously). We haven't found anything out of the ordinary in event viewer or on the ports themselves.

Here's statistics for one of the ports that has an issue:

Receive Statistics
Total Bytes(Octets)      163202131      
Unicast Packets      609258      
Multicast Packets      668      
Broadcast Packets      1383      
Packets with Errors      0      
Packets Discarded      7      
 
Transmit Statistics
Total Bytes(Octets)      522517034      
Unicast Packets      751359      
Multicast Packets      58472      
Broadcast Packets      129920      
Packets Discarded      13
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masnrockCommented:
You should get a tool like Wireshark or PRTG into use so that you can start monitoring the traffic. That may start to give you an idea of what's going on.
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Lee IngallsDirector of IT/TS, Quality and FinanceCommented:
I spent several months addressing intermittent slow network.
It feels like chasing a ghost...
What's the environment look like?
Server OS?
Virtualized?
Workstation OS?
Storage environment? SAN, NAS or DAS?
SMB1? SMB2?
Updated NIC drivers, etc
I used IOMeter, Wireshark and Performance Monitor to capture data.
Depending on the environment I can provide more detail.
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street9009Author Commented:

I spent several months addressing intermittent slow network.
It feels like chasing a ghost...

Boy, you got that right.

The environment consists of several servers, all physical boxes. There are a couple Hyper-V servers running on one of them but they aren't asked to do much. Servers are a mix of Server 2008 R2 (2), Server 2012 (1), and Server 2012 R2 (the rest). All servers have their own physical RAID (SAN, NAS, etc.). There are several shares that get mapped to network drives (standard).

No changes to drivers on any of the servers that I am aware of. There is one new box in the mix but it's now been turned off just to be sure there's nothing there causing an issue. It's not in production... yet.

Workstations are primarily Windows 7 but there are some Windows 10 (I am one of them). Windows 10 does seem to be unaffected by this. There are Windows 7 stations that are fine and some that aren't, but I've yet to find a Windows 10 that was slow. Could be coincidental.
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masnrockCommented:
A weird random issue I have seen happen before required simply disabling IPv6 on the NIC of the domain controller.
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street9009Author Commented:

A weird random issue I have seen happen before required simply disabling IPv6 on the NIC of the domain controller.

It's disabled on both already. It's typically not left on for any machines with a static IP. DHCP doesn't hand out IPv6.
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street9009Author Commented:

All servers have their own physical RAID (SAN, NAS, etc.).

Sorry, that should read NO SAN, NAS, etc.

I'm starting to believe that whatever the issue is, Windows 7 is more susceptible to it. I haven't seen a single 10 client that has an issue. May try to upgrade one and see what happens.
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Lee IngallsDirector of IT/TS, Quality and FinanceCommented:
Windows 7 clients with Windows 2008 r2 servers has an issue with SMB2. It can be disabled by registry entry. Additionally, TCP and UDP checksum offloading can be disabled on the NIC's. This combination made a significant improvement for me!
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street9009Author Commented:
We made these changes via Group Policy (registry entries) and pushed them out. It does seem to have helped. I'm a little concerned that this is still masking an underlying problem (as we had no issue until 10 days ago) but the network does seem more stable and the users that were complaining are no longer having trouble.

Thanks for pointing us in this direction!
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