Network Lag…
March 28, 2008 · Print This Article
Recently I received a call from an IS manager who described with great anguish, his local network lag time. He reported to me that his client’s access to a local file server was jaw droppingly slow. He went on to tell me that after checking the configurations of the switches and the file server, he did not see any irregularities. He could access other servers on the same network segment but for some reason he was having issues with this particular server.
Here is a visual:
As you can see I ran traces on the different network segments and I focused most of my attention on the file server/ media convert/ switch. I did not find any configuration issues with any of the network equipment and the file server seemed to be doing its job. After running the traces I did notice that packets were being dropped at the file server and runts were being detected.
In my experience physical connections/hardware or configuration is the leading cause of dropped packets. Since my customer thoroughly checked his hardware, the configuration piece could still be a problem. Looking back at my traces, there is one segment that could still be misconfigured. The inbound switch and the client computers.
…Conclusion
As you might expect, there was a configuration issue but it wasn’t as obvious as you might think. The clients were set to auto negotiate and the switch was hard-coded at Full duplex, the Windows clients could not negotiate a duplex with the switch and subsequently defaulted to half duplex, creating a mis-match.
Because of the duplex mismatch, packets were being dropped and therefore never made it to the File Server for acknowledgement.
The dropped packets caused retransmissions from the client, which resulted in huge network latency directly effecting the end-users.
To correct the issue the configuration of the client or the switch will need to be modified to allow proper duplex negotiation.
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