Intermittent Network issues between server and client machines

Posted on 2011-09-09
Last Modified: 2012-05-12
Hey everyone,

Having an issue that is really kicking my ass over here.  For a while now I've been dealing with intermittently slow network access at one of my clients, where, for instance, at random times throughout the day they'll open a word document and it'll take 30+ seconds to open it and it has a download bar at the bottom of Word.  This will happen for  several documents and then stop.  But this is with different programs, not just Word.  

I have the AntiVirus scans turned off, Firewall Off, tried a different switch and cables, I ran Wireshark and it was giving gopher requests errors and that's why I disabled the Checksum Offload on all of the NICs.  When they access files these come up in Wireshark:

Header checksum: 0x0000 [incorrect, should be 0x5db3 (maybe caused by "IP checksum offload"?)]
Duplicate to the ACK in frame: 647
This frame is a (suspected) fast retransmission

Here are the NIC settings for the server (I've tested with most settings individually over time):
Ethernet@WireSpeed = Disabled
Flow Control = TX & RX Enabled
Interrupt Moderation = Enabled
IPv4 Checksum Offload = None
IPv4 Large Send Offload = Enabled
Jumbo Packet = 1500
Locally Administered Address = Not Present
Number of RSS Queues = Auto
Priority & VLAN = both enabled
Receive Buffers (0=Auto) = 0
Receive Side Scaling = Enable
Speed Duplex = 100 Mb Full (this used to be 1Gb Full but we're testing a different switch)
TCP Connection Offload (IPv4) = Disabled
TCP Connection Offload (IPv6) = Disabled
Transmit Buffers (0=Auto) = 1500

NIC Settings for the Client Machines:
Ethernet@Wirespeed = Enabled
Flow Control = Disabled
Interrupt Moderation = Enable
Large Send Offload (IPv4) = Enable
Large Send Offload v2 (IPv4) = Enable
Large Send Offload v2 (IPv6) = Enable
Network Address = Not Present
Priority & VLAN = both enabled
Proxy ARP Offload = Enable
Proxy NS Offload = Enable
Speed and Duplex = Auto
TCP/UDP Checksum Offload (IPv4) = Disable
TCP/UDP Checksum Offload (IPv6) = Disable
WOL Speed = Lowest Speed Advertised

The last time I did a copy/paste on a file it went right away, now for some reason it's transfering at 100-150KB per second which is obviously way to slow.  

I'mn honestly at a total impass and banging my head on the wall as are my clients.  Any help would be immensely appreciated.

Question by:blue92lx
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Author Comment

ID: 36512615
Also I just did an internet speed test on the server and a client machine and I'm getting 5Mbps download on both.

Then I did a copy from a client computer to the server and it was copying at 5MBps, but if I copy from the server to the client it still copies at 100-150KBps.

Expert Comment

ID: 36512617
do you use fiber optic cables
what kind of switches are you using

Author Comment

ID: 36512678
Right now the switch is a standard Linksys 16port unmanaged switch.  Regular ethernet cables, no fiber optics
Portable, direct connect server access

The ATEN CV211 connects a laptop directly to any server allowing you instant access to perform data maintenance and local operations, for quick troubleshooting, updating, service and repair.


Expert Comment

ID: 36512851
and that switch is with external ac adapter ?

Expert Comment

ID: 36512862
if so test it by a multimeter secondly you need to swap the cable between client and server then the nic card on the client

Expert Comment

ID: 36512978
Is this only for Office documents?

Author Comment

ID: 36512992
This is an issue for anything network related. Like I was saying even doing a copy/paste has issues.

Also the switch is the 2nd switch we've used and I tried today with a new ethernet cable and neither worked.

Accepted Solution

nativevlan earned 500 total points
ID: 36513006
If the switch is unmanaged you will want to set the server nic to auto. The switch won't be able to negotiate speed duplex if the nic is statically configured and it will default to half duplex.

Author Comment

ID: 36513304
I am so unbelievably angry right now because NativeVLan's answer was correct.  I have dug through every single aspect of every computer on this network without an answer and I have never in my 5 years of IT seen a server set to auto, or for that matter, I have never set a NIC anywhere to a manual speed/duplex setting and had it run worse.

Native you saved my life because I know if I was getting fed up and angry then my clients must be ready to throw something through the window.  A million points to you sir

Expert Comment

ID: 36513334
No problem. I just had the same issue a few days ago :)

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