Intermittent Network Slowdown - General networking



  • This isn't an issue with our PfSense unit, but I though I would post it here to see if anyone has any suggestions because this one defies logic and my next steps are going to be time consuming which I would rather avoid.

    Running a small office behind a XG-1541, each segment has a Cisco 3750e or equivalent switch off of the unit which then goes to office outlets, or in this case another network closet with another 3750e and then the office. The whole network is 1Gbps.

    One particular office has a problem where occasionally for long periods of time it will only be able to get 15Mbps. When it happens it isn't due to network congestion, I've verified that no large file transfers are happening inter-office and the internet is barely being used. It has a Cisco small business desktop switch off the outlet before going to a dozen systems, I don't have the model at the moment but it doesn't matter. It should be able to handle the traffic as the backplane is rated for 48Gbps, and I tried swapping it with another 3750e as well with no change. If you bypass the router though and connect a computer directly, the problem is immediately gone, this is why I swapped the router out, I assumed it was the problem. Also if you leave it alone eventually it will go back to full capability but there is no indication of why, or guarantee as to when.

    After swapping the router, I tried swapping the outlet as there is a second one in the office used for a department file server which doesn't seem to have a problem, but when I did so the problem remained, and yet again with a single computer connected to the outlet there is never a problem.

    So: Different switches different network runs, same problem with bandwidth. I ran a tracert to see if there were delays but everything was fine. Just to make sure I patched that outlet directly to the main segment switch off the firewall with new patch cables, same problem. I left it alone for a couple hours to work on something else and when I came back it was fine, for an hour or two at which point it back to being slow.

    The switch in the office recognizes it as being a 1Gbps connection to the wall and each computer, However I am not certain of the quality of the cables in the wall for that office. Everything I've done is CAT6, but that run was done before I started. But if the run was cheap cable to that office then why does it work sometimes and not others? And why does it work with a computer connected direct but not with an intervening switch?

    My next option is to try and configure the switch to use one port put a packet sniffer in place on that switch, and another on the main one and compare the actual traffic, but I would rather avoid that if I can.

    Any Ideas? Am I missing something?


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