Yes, this is usually one of the most difficult problems to diagnose and resolve. It’s not always a matter of sheer speed. Here are a few general principles to keep in mind when troubleshooting such issues:
- Users are subjective. First of all, make sure that the problem being described is actually a problem. Users can be somewhat ambiguous when describing performance. Compare experiences of multiple users at a site, and if possible, take a look for yourself and see first hand what is being experienced.
- Once you’ve verified that there is indeed a problem with network performance, check, as you did, that computers are connecting at the best possible speeds (1 Gig whenever possible) and that speed and duplex settings are correct. Check for CRC errors and packet drops, once again, as you did. If you have errors on the interface, check cables, faulty QoS mechanisms, as well as the possibility of a faulty port or NIC on the PC.
- If you have routers in the mix, do some ping and traceroute tests with various sizes in order to see response times as well as to check for optimal routing paths.
- With your ping tests, check to see what kind of MTU sizes are being allowed between source and destination. If there is a smaller MTU somewhere and packets are being fragmented, this could slow down your network. If packets are set not to be fragmented, then this could result in packet loss.
- Specifically for your issue, if you are using SMB for file sharing, try setting up an FTP server on the file server and do a test transfer of a large file from a client computer to the server. If the transfer goes smoothly, then the network may not be at fault, but some configuration of the file sharing server software setup.
- If users are connecting at 100 Mbps, it could be that this speed is just not enough. Consider upgrading to gigabit ethernet NICs. Try upgrading one and test the results to see if this affects the overall performance.
These are just some thoughts that will hopefully get your creative juices flowing. Troubleshooting such issues all comes down to experience. If you’ve seen something like it before, you have a deeper understanding and your mind approaches the solution faster. It does take time though. Problems that result in a complete disconnection of the network might sound more devastating, but are definitely easier to diagnose and solve than issues like the one you describe. But not to worry, with time, a lot of reading, and personal experience, it does get easier and more intuitive.
Some lessons that might help you in your quest include the following:
I hope this has been helpful!